For radiation protection measurements such as the regular bunker survey we always report in Sv. The radiation safety section is just wanting to see that we are keeping below the recommended limits, actually (unwritten approach) 1/3 public and ALARA on worker limit. All our survey meters report in Sv (well microSv/hr). Radiation incidents are generally also reported in (m)Sv. There is mandatory reporting if we cause "an unplanned or abnormal exposure to ionising radiation, other than a justified medical exposure, exceeding 1 mSv total effective dose". Although there is also "A human diagnostic procedure that results in a skin dose that exceeds 6 Gy."

@Lindsay

This does address my question. Survey meters calibrated in Sv and radiation delivery in Gy. Likely the calibration is intended to be Hp(.). Is Gy reported based on medical physics procedures? Are Gy strictly calculated or calculated from calibration with phantoms?

While ICRU has standard definitions and measurement methods, there is no clear definition of when Sv and Gy should be used. I have heard differing opinions on when to use Sv or Gy with no resolution even when the definitions are displayed. Do you have institutional procedures for when to use Sv or Gy?

Radiation due to radioactivity has 2 SI units namely, Gray and Sievert. Both, serves for different purposes of measuring radiation.

Radiation is of 2 kinds,

1. Absorbed Radiation

2. Equivalent Radiation

ABSORBED RADIATION:

Absorbed radiation is the 1 Joule of Energy absorbed by 1 Kg of Matter.

EQUIVALENT RADIATION:

Equivalent radiation is the 1 Joule of Energy absorbed by 1 Kg of biological tissue.

DIFFERENCES BETWEEN GRAY AND SIEVERT:

Though both these units appear similar on their formulas, difference is accounted based on the body where absorption occurs. Hence, SI unit for Equivalent Radiation i.e, Sievert carries much weight since it concerns for the radiation which occurs on the living objects.

Measurement of radiactivity:

Curie (Ci): Quantity of any radionuclide in which the number of disintegrations per second is 3.7 x 1010 . 1 Ci = 3.7 x 1010 disintegrations per second (dps)

Becquerel (Bq): The International System unit of radioactivity, equal to one disintegration per second.

1 Ci = 3.7 x 1010 Bq

1 Bq = 2.7 x 10-11 Ci

Measurement of absorbed doses and biological damage:

- Old units

RAD: Radiation absorbed dose. A unit of energy absorbed from ionizing radiation, equal to 0.01 joules per kilogram of irradiated material. This unit is not used anymore. It has been replaced as a standard scientific unit by the gray.

The difference between the rad and the gray is a proportionality factor: 100 rads equals one gray

REM: Roentgen Equivalent Man. The amount of ionizing radiation required to produce the same biological effect as one rad of high-penetration x-rays. This unit is not used anymore. It has been replaced by the Sievert: 100 rems equal one sievert.

Roentgen

Amount of x-ray or gamma ray radiation (electromagnetic radiation) that produces 1/3 x 10-9 coulomb of electric charge in one cubic centimeter of dry air at standard conditions.

Although the roentgen describes a different property from energy absorbed per unit mass, the effect of one roentgen on dry air is roughly equal to one rad. This unit is not used anymore. It has been replaced by the rad and later by the gray.

- Current units

Gray: The IS unit for the energy absorbed from ionizing radiation, equal to one joule per kilogram. An absorbed dose of one gray is equal to the absorption of one joule of radiation energy by one kilogram of matter.The gray is the correct unit to use when you wish to monitor energy absorbed per unit mass.

Sievert: The IS unit for the amount of ionizing radiation required to produce the same biological effect as one rad of high-penetration x-rays, equivalent to a gray for x-rays. It measures the radioactive dose equivalent. One sievert is equal to one gray multiplied by a relative biological effective factor, Q, and a factor that takes into account the distribution of the radiation energy, N. The sievert is the correct unit to use when you wish to monitor the biological danger of radiation.

1 gray (Gy) = 100 rad

1 rad = 10 milligray (mGy)

1 sievert (Sv) = 1,000 millisieverts (mSv) = 1,000,000 microsieverts (μSv)

1 sievert = 100 rem

1 becquerel (Bq) = 1 count per second (cps)

1 curie = 37,000,000,000 becquerel = 37 Gigabecquerels (GBq)

For x-rays and gamma rays, 1 rad = 1 rem = 10 mSv

For neutrons, 1 rad = 5 to 20 rem (depending on energy level) = 50-200 mSv

For alpha radiation (helium-4 nuclei), 1 rad = 20 rem = 200 mSv

@Jorge

I agree with the definitions you have given and how they should be used. I use the definitions as in ICRU 57. One difference Sv is effective dose, not equivalent dose.

How are doses reported in your institution, Sv or Gy? Does your institution procedurally define when use Sv or Gy? Do you still use rad and rem?

Dear Joseph. I worked by the IAEA and we use in this organization the current units included in my reply. Now, I am writing on nuclear and other issues.

@Jorge

I was looking for practical experience and problems with using the definitions.

@Others

A possible restating of the question, Do you think there should be standard guidance for the use of the terms Sv and Gy?

A. Use Sv for radiation protection and use Gy for therapeutic and diagnostic purposes.

B. Use Sv for radiation and diagnostic purposes and Gy for therapeutic purposes.

C. Use Sv for all recorded doses and Gy for calculation of equivalent dose.

I see some practical problems since Hp(.) is used to calibrate instruments. In particular skin dose is defined as Hp(0.07) as Sv, but for dose assignment it must be multiplied by 0.01.

Dear Joseph. Now the question is much clear. The old units were changes because some problems were identifed with their practical use. The new units were defined precisively to overcome these problems. For this reason, I do not see the need to define now standards guidance for the use of the new units. I think the new units should be used as been defined.

Worldwise there is no uniformity for measurement of absorbed dose, Some instrument measure in Gy whereas some in Sv. I am not aware about your county specific reporting guidelines but in general you are free to report your results either in Gy or Sv without changing by applying any factor.All the instruments used for therapy purpose uses Gy whereas instruments for radiation protection purpose uses Sv or R and sometimes Gy too. but now a days these radiation protection instruments are trending towards use of Sv.

In India, we use Sv for reporting Dose to the workers

Absorbed dose is Gray, effective dose is Sievert.

For diagnostic radiography in the UK, we record the dose area product (DAP) from the DAP meter for every examination, this is in Grays (Gys.cm2 to be precise) - it is an instant readout. These are used to monitor our doses in relation to diagnostic reference levels. If an examination consistently exceeds a DRL then there is an investigation (is it technique, equipment etc etc?).

Sievert is used to communicate the risk from radiation. If a patient askes me "what is the risk of radiation from my abdominal CT" - I can tell them "It is approximately 8mSv, which is the same as 3 years background radiation in the UK. 1mSv increases your risk of cancer by 1:20000 and this is on top of your lifetime risk of cancer being 1:3" (in communicating risk from radiation to my patients I also use the lottery ticket analogy - you have to buy one to be in with a chance - but just because you bought one doesn't mean you will).

You cannot get an instant readout of effective dose (Sieverts) because it is an estimation based on field size, type of radiation (x, alpha etc) and the body part irradiated (tissue weighting factor). There are also 3 different ways of estimating Sieverts - ICRP 60, ICRP 103 and NRPB60 have different conversion factors. ICRP 103 is the most up to date (from 2007).

(let me know if you want the references for the above).

In Romania we use dosemeters calibrated in H*(10) - ambiental dose - for area monitoring, Hp(10) for personal dosemeters and Dw (absorbed dose to water, in Gy) for therapy dosemeters. It all depends on what you need to measure and the law says you should report Sv - either ambiental or personal dose, not effective - for radiation monitoring (like in area or personnel) and Gy for therapy irradiation (where the prescription doses are also in Gy). Also DAP is used for diagnostic radiology, in an attempt to keep the doses under a recommended level per investigation (but that is not a limiting level, just a recommendation).

I agree with Jorges statements and I am following this preception:

There are two groups of doses, the physical doses "absorbed dose, KERMA both described by Gray and the ion dose or exposure measured in C/kg without special name.

The second group of doses are the radioprotection doses with the unit Sv without any distinction. Here I see a practical problem. The equivalent dose with its subtypes Hp etc. are mesurable physical quantities.

The second part of the radiation protection doses are the organ dose and the effective dose. They can´t be measured just calculated. Organ doses contain radiation weighting factors similar to the equivalent dose. Effective dose describes the radiation risks using the wT factors. Here you really won´t find any absorbed energy, it´s a completely different description.

My proposal is, use the Sv for really measurable radiation protection doses but

I would appreciate to get a new dose units for the effective dose because I have the impression that there is some confusion about the widely misused "Sv".

@Hanno

I agree a new dose unit is necessary. The answers by Fiona and Radu show some of the problems. My experience is that a unit is necessary between Gy and Sv. I disagree that Sv should be used for measurable quantities. Sv is defined by ICRP as risk. This definition is not clear, hence the problem with using it.

The definition of Sv as risk is by use of reciprocal Sv in the risk coefficient of the LNT. In order to use the risk model, effective dose using weighting factors must be calculated. Granted, a new unit could be used for the risk coefficient, but I think there is too much precedent to change.

A unit is needed between Gy and Sv, because simple reporting of Gy or Sv does not tell anything about the process. If we stay with these two units there should be a requirement for description with the units, e.g., X Gy Hp(10) and at least a footnote for any weighting factors.

Dear Joseph,

really no problem with the unit "between". If you limit the Sv for risks, the only dose is the effective dose, where you can use it. The measurable radiation protection doses, which are absorbed doses with weighting factors, then should not use the Gy. I´ve no idea, which name then should be used. Absorbed dose has a very clear definition (absorbed energy/mass), no weighting for radiation quality.

Hanno

The use of Gy for Kerma and absorbed dose is unambiguous as you stated. Energy absorbed per unit mass is quite simply what is meant by energy/mass. The problem is the weighting factors and the calibration definitions such as ambient dose. Because there are so many (ICRP 26, 60, 103, ICRU 57, and national regulations) a single name becomes a problem. My suggestion is Gy(H) with a required definition of H. This would propagate through to Sv.

Those who think this is not necessary has not done dose reconstruction or tried to combine doses from several projects.

Dear Joseph,

have to think about your proposal. Indeed using the Sv for Hp, H(0,07), H*, H´etc is misleading. You always need complete descriptions, like Hp for Alphas, enlarged field etc (you know all these possibilities). So your idea seems to be plausible.

PS: Have a short look on some answers about the Q to "often X-ray using", where you posted comments. There in the answers of collegues again the mSv is used without any specification (eff, Organ dose ??).

Hanno

Exactly! To all you wrote.

Most radiation protection situations concern external gamma, whole body. While this in no way constitutes Hp(10) we accept it as a reasonable approximation. Problems arise when the approximation does not apply. Often, it does not apply when we must examine the approximation for cases of over exposure or unexpected exposure.

Many radiation protection situations do not fit the approximation, yet they are treated as though the do. As you stated, mSv is used without specification. There is no information to determine what mSv is meant. There is insufficient guidance in the use of radiation protection quantities.

I do not advocate more rules and regulations, but I believe that the current ICRPs and ICRUs need a little more in the area of application.

Please dear Joseph, propose a practical procedure to to talk to the "important" people in ICRP and ICRU to cause a change.

Cray is for absorbed dose and Siveirt is used for effective dose. the first is the energy deposited per unit of matter.  the second using weighting to radiation and tissue factors. they measure different things

@Wagner:

You are right, but you forgot, that Sv is also used for eqivalent dose, organ dose, personal dose and Hp(10), Hp(0.07). And the Gy is also used for Kerma, the transfered energy to secondary charged particles of the first generation.

So, what we need is a better distinction of these different kind of doses by their units.

 By the hand all these dose terms  base on the absorbed dose. They are derived by modificating them with factors for radiation quality and risk factors.

Allow me to clarify....

Absorbed Dose (Gray) is  purely Physical  as measured by radiation dosimeters (e.g. ion chamber, diode, TLD, film,  etc). The unit of  1 Gray = 1 J/kg - is simply the concentration of physical energy absorbed locally from the radiation exposure.

Effective Dose (Sv) wasintroduced to help incorporate the Biological impact of radiation but it still relies on the same fundamental dimensional unit (J/kg). It is the Physical Dose (in Gy) multiplied by unitless factors, such as Radiation Weights to account for different types (LET, RBE) of radiation, and/or Tissue/Organ Weights to account for differential radiosensitivity/importance of each organ to human survival. Dose rate corrections can also be applied. The origin of the organ weighting factors is poorly explained in ICRP documents. They are rough estimates, in my view, with unclear justification. 

Effective Dose (Sv) - The individual effective organ doses (in Sv) are summed together in a weighted fashion to yield a virtual whole-body Effective Dose. The Effective Dose is intended to match "overall risk" of a partial body non-uniform radiation exposure to a whole body uniform exposure.

Risk Estimation- The Effective Dose is often multiplied by risk-conversion factors derived from Japanese survivors with whole body exposures (e.g 5% per Sv of Effective Dose) to estimate the probability of a radiation -induced cancer death. Again  this is just an estimate for a similarly exposed population - not to be used for an individual exposed person.

In brief, dose (Gy)  is easy to measure physically...Effective Dose is much more complex, debatable,  and requires 'biological inputs' with very large uncertainties.

Radiation Protection is not (yet) at the accuracy level of Radiation Dosimetry !

I hope this helps...

J2

@Jerry

The question concerned the use of Gy and Sv as practiced by your institution or regulatory agency.

Hi Jos...

Sorry ..I lost the thread of the original question and thought I could help by some crisper definitions.

I agree that Radiation Protection Quantities are indeed scientifically "muddy" and often ill-specified. To be fair, we do not have much human data at low dose exposures to individual organs (Tissue Weights) and this may be the limiting factor.

Different quantities are used for different purposes at our Institution, depending on the purpose:

For radiation protection purposes on a radiotherapy installation, Absorbed Dose (Gray) in Soft Tissue (e.g. Muscle or water) remains as the main regulatory measurement obtained during Megavoltage  x-radiation surveys (often converted from the old Roentgen or Air KERMA reported by the instrument).

If any device reports in Sv (e,g. for neutron exposures), it  makes internal assumptions about the radiation type/energy  - suspicious of such values. The device certainly cannot apply Tissue Weightings and hence cannot produce the "whole body effective dose" that I described in my "lecture"/

For clinical radiation oncology, we use BIG doses (e.g. 70 Gray in total) and stick to physical Absorbed Dose (Gray) as much as possible to specify prescriptions at a reference  point or volume edge. Dose-Volume histograms often are used to assess the tumour coverage and organ sparing levels. We sometimes also calculate the Biologically Effective Dose (BED) to compare treatments with different total or fractionated dose size or dose rate. This is NOT the effective dose used in radiation protection.

For diagnostic Medical Imaging (e.g. CT), the local dose is first measured (e.g. central axis reference conditions such as DAP or multiple small dosimeters are placed within  in a RANDO phantom)  and Effective Dose is then calculated while specifying the ICRP version of weighting factors applied. For CT the DLP is often used and can be approximately converted to Effective Dose for a specified anatomy.

I hope this helps...

@Jerry

I agree that we do not have enough human data for tissue weights. The weights are assigned (good or bad) and we have directions on how to apply. The problems in interpretation I have encountered are interpreting results that are scattered between kerma and effective dose.

My experience is that medical applications tend use the terms correctly, but may not sufficiently indicate if any weighting factors were applied. It is interesting that you use strict absorbed dose in some applications and effective dose in others.

My experience in radiation protection is that most know the rules but rely on calibration to effective dose. Calibration can be made to the calibrating conditions and may not remotely apply to the measurement situation.

All

Thank you for your input. My suggestion for use of Gy and Sv is 

Gray shall be used strictly for energy deposited. Sievert shall be used for effective dose.

The restriction of Gray to energy deposited requires that no weighting factors or conversions be applied. When reporting Gray, the method of determination shall be included. For routine reporting of Gray reference shall be made to a method or procedure.

Energy deposited that is converted to equivalent dose shall be designated Gy*. The conversion method shall be included parenthetically or footnoted.

Effective dose is reported as Sv after conversion from Gy*. The Gy* method shall be included.

I like  your suggestion !

We must clearly distinguish the quantities  Absorbed Dose, Equivalent Dose, and Effective Dose via symbology. I would add subscripts or superscripts to specify the method or factors used.

For standard Effective Dose, superscripts/subscripts could  be used to indicate  factors used to avoid confusion.

e.g. Effective Dose  with Units of SvICRP103 .

e.g. Equivalent Dose with Units of Gy10 for a radiation with a weighting of 10.

---------------------------------------------------------------------------------------------------------

CAUTION: This technique is used in radiotherapy for Biologically Effective Doses (BED) relying on a cell-survival parameter ratio called alpha/beta. Its value is often specified as a subscript,as follows:

e.g. BEDs are in units of Gy10 where 10 is the alpha/beta ratio used. To be more consistent Sv10 would be better because it is intended to have 'biological impact meaning.

-------------------------------------------------------------------------------------------------------------

This merits further thought to "fix it once and for all"  across all disciplines, but we are on the right track, Joseph !

J2

@Jerry

Good suggestion. I like your last statement, fix it once and for all.

Dear all, I´m happy to read "movement" in the ideas and proposal. No we have to convince the officials.

The gray (Gy) is the only actual physical dose ! 1 Gy = 1J/Kg

But the effect of the radiation dose on the body changes with the radiation type. Beta and Gamma are quite equivalent but Alpha is much more dangerous.

So we use the equivalent dose to consider the danger of different radaitions.

For instance, 1 Gy (1 J/kg) of Alpha is 20 time more dangerous than 1 Gy of gamma.

So 1 J/kg (physical unit) of Gamma absorbed dose corresponds to 1 Sv of equivalent dose

and

  1 J/kg (physical unit ) of Alpha absorbed dose corresponds to 20 Sv of equivalent dose!

Now the different tissues of the body arer differently sensitive to radiations

So we use the effective dose to consider the effect of a radiation on organs.

The ovaries are 20 times more sensitive than the skin.

For calculation:

Absorbed dose:  D (Gy)

Equivalent dose : H : Wr . D (Sv)

Effective dose:   E = Wr . Wt . D (Sv)

For simplicity, the sum of all Wt = 1

So  1 Gy of Gamma on the skin (Wr = 1, Wt = 0.01) gives 1 Sv of equivalent dose and 0.01 Sv of Effective dose.

But 1 Gy of alpha on the avaries (Wr = 20, Wt = 0.20) gives 4 Sv of effective dose,  400 times more risky than gamma on the skin (the previous case).

There is still a lot of confusion in the use of these units because, at high doses, all radiaiton are deadly so the Sv is only valuable for low doses but we find pubilications in radiotherapy mentionning doses of 100 Sv !!!!

The sievert is used to consider the RISK of appearance of a disease. It is only statistically valuable: With a dose of 100 mSv,the risk to see a cancer in the next 20 years in two times higher than with a dose of 50 mSv BUT ONLY THE RISK maybe not the reality for a person considered alone.

A dose of 100 Sv effective dose leads certainly to the death as well as a dose of 50 Sv !!!!

Another confusion comes from the same unit (Sv) to speak about equivalent dose and effective dose.

Some people propose to use the Taylor (Ty) for the Effective dose. This is not yet approved because most of the time we know what we are speaking about.

I think that it should be useful to use different unit for different entities.

Jean Louis Genicot

@Jean Louis,

I think all the collegues in this thread know your statements, because all of us are working in theoretiacl and practical radiation protection and dosimetry.

The mixing up of equivalent and effective dose by the same unit is the reason for this discussion.

I have no problems to use the established doses and units, but read some papers or discussions, you will see a lot of confusion.

BTW: Using effective doses of 100 Sv is completely nonsense, because effective dose is defined only for stochastic risk and not for deterministic insults and tissue reactions.

@ Hanno,

You confirm what I wrote about the non-sense of 100 Sv.

If you look in Office of Science, US dept  of Energy, you will find a pdf file about a dose range chart.

Just type "dose range office of science dept of energy" in google and you look at the first result.

@Jean,

Thanks for the hint. But besides the old units, it´s still nonsence to use the Sv or rem for deterministic cases even this pdf shall be an official information. We have clear definitions in ICRp 103 and a lot of informations about radiation effects and the dose ranges. If you allow, I attend a chapter from one of my textbooks about dose definitions. I regret it´s in German, but you will surely have no problem to understand.

Okay so much confusion... now I will try.

Gy is something that is a measure. Sv is what happens when a person is standing at the same place you measured.  So if no person is in the picture there is no Sv. There is only R or Gy.  In other words there is only exposure at a point in space (and no dose).  Think of it as a bottle of pills where the pills have a concentration of active ingredient.  As long as no one takes the pills there is no "dose" there is only a quantity.  It is not until the quantity enters the human body can we begin to discuss dose.  In the case of pills the confusion remains as to how to report.  For example the prescription may say two pills every 4 hours... this is not a dose since dose would follow milligrams per kilogram of human and there may be other factors such as per age or gender. The same follows exactly as joules per kilogram in air verses joules per kilogram tissue and then we get even more specific when we talk about quality (type of radiation) and tissue type where and when we discuss relative biological effect.  But these aspects are not what you are looking to resolve with your question which is simply When is the term Gy correct and when is the term Sv correct.  Gy is what you convert from activity detected by your meter and Sv is what you report as that activity that is in the human body (since now in the human body is a dose but loosely stated until we define kilograms etc.).

@ Joseph

I understand your concern of using the instrument reading for practical reporting purpose. I agree this is highly confusing subject but i can tell you what the people doing practically.Most of the older instruments were providing doses in terms of rem or R (per hour in case of survey instruments) and people are accepting the reading as it is without any correction factors. However in recent past years almost all field instrument gives reading in terms of R or Sv (per hour in case of survey instruments). New era instruments have the beauty that they are calibrated in terms of Hp(10) or H*(10), this make sense to adopt the readings as it is.

Further in case of instruments providing in terms of Gy and used in gamma/beta  fild for whole body dose (oe effective dose measurement), readings can be adopted as it is in terms of Sv, which gives good approximation. In case of Gy in the fields of  other radiation type OR measurement of equivalent doses, it may require to utilize necessary correction factors.  Further for regulatory purpose much accuracy may not be required for survey dose rates (or exposure rate) so these may again used for good approximation.

I agree with Jean Louis M Genicot's answer 

After the answer of Jean Louis M Genicot nothing more needs to be said. Perfect in its definition

Effective dose is intended for use as a protection quantity. According to the definition provided in ICRP Publication 103 issued in 2007, effective dose is calculated for a Reference Person (equivalent dose for Reference Male and Reference Female), but not for an individual.

For tissue reactions (formerly called deterministic effects or nonstochastic effects), the use of effective dose is inappropriate, and the use of the RBE weighted absorbed dose (not equivalent dose) is preferable at high dose.

The assessment and interpretation of effective dose from medical exposure of patients is problematic when organs and tissues receive only partial exposure or a very heterogeneous exposure.

Nobuyuki

These definitions have been addressed in other answers. The ICRP and regulatory agencies are the sources of confusion. There has been no effort to clarify use of units and when to report which type of Gy or Sv in a given situation. There has been no effort to identify which type of Gy or Sv was used in a report.

Do you have a suggestion for how to clarify the units for any given situation. How does your country or agency require units to be reported?

You may have been aware of the ICRP Task Group 79 (TG79) on effective dose, which is producing a report to provide guidance on when the quantity ‘effective dose’ can be used and when it should not.

TG79's discussion paper published last year can be downloaded from

http://journals.sagepub.com/doi/pdf/10.1177/0146645316634566

At the ICRP website, the draft report may come out for public consultation before long.

From radiation protection viewpoints, the current Japanese regulations are basically predicated on the ICRP 1990 Recommendations (recommended in ICRP Publication 60). For individual monitoring, the effective dose and the equivalent dose to the skin are measured using operational quantities Hp(10) and Hp(0.07), respectively, barring neutron fields in which only Hp(10) is exclusively measured. Hp(10) or Hp(0.07), but not Hp(3), is used to estimate the equivalent dose to the lens of the eye.

Nobuyuki

I read the TG79 draft. They are correct on confusion, offer nothing on clarification. Sv is a poorly defined. It uses energy units for risk, when risk is intended. The Sv is for low dose stochastic risk, not deterministic risk. The committee offers no method for interpreting reported units. One must add information to clarify which type of dose and as calculated by which ICRP publication.

I do not have much hope for TG79 fixing anything.

The US NCRP will no longer recommend equivalent dose limits for prevention of tissue reactions (deterministic effects), and instead, recommend the use of RBE-weighted absorbed dose for high-LET radiation. Somewhat similar discussion is ongoing in ICRP.

The draft report "The Use of Effective Dose as a Radiological Protection Quantity" prepared by ICRP Task Group 79 is now open for public consultation, which will end on 3 August 2018. The draft is attached FYI.

http://www.icrp.org/page.asp?id=382

Sv is used only for worker exposure management. This is additive for different radiation types and energies. Gy is defined by the absorbed energy for the substance. It is a physical quantity.

A very healthy informative discussion on the initial question. After going through ICRP, Task Group79 Draft, the confusion regarding the use of units seems to be is resolved but it was always there when discussion started 4 years back.

The TG 79 draft is much improved and addresses most of the problems of when to use Gy or Sv. Indeed, most of the document is easily understood, something that ICRP has not accomplished in the last 50 years. The document is obviously the work of a committee, because too much is included that is not necessary to the intent. Nevertheless, a step in the right direction.

Already commented TG 79 Draft report is a step forward. Agree with Josep point of view regarding over elaboration of draft but many aspects needed that also, anyhow its committee report, one can differ individually in this respect.

Types of ionizing radiation are divided into photon (gamma radiation and X-ray radiation) and corpuscular (alpha, beta particles, protons, neutrons, etc.). Ionizing radiation can perform ionization of substances directly or indirectly through secondary effects. Neutrons and other neutral elementary particles and quanta of electromagnetic radiation do not directly produce ionization of matter, but in the process of their interaction with the medium, charged particles capable of ionization are released. The main physical quantity and measure of the effect of radiation on materials is the absorbed dose. The absorbed dose of ionizing radiation D is the ratio of the average energy dE transferred to the ionizing radiation in a unit volume to the mass dm of the substance in this volume. The concept of absorbed dose is applicable for all types of radiation, is a measurable quantity (Gy). The influence on the environment of indirectly ionizing radiation at present must be evaluated using the concept of kerma (K). It is also measured in Gr. For photon radiation in air, it is the energy equivalent of the exposure dose (X), which has been taken out of use. Kerma does not include losses due to bremsstrahlung g = Kt / K. For light materials (air) and for medium energies g are small, for media with large Zeff and at low energies, g can be significant. If the losses to bremsstrahlung can be neglected under electron-equilibrium conditions for air K = X ~ D. The values ​​of the effective and equivalent doses (H), (3B) introduced for use only in small doses are purely calculated values ​​and are defined as the photon kerma in air multiplied by the weighting coefficients WR and WT. WR (Sv / Gy) - takes into account the quality of different types of radiation, is determined depending on the total linear energy transfer of LET (keV / μm). WT is a weighting factor for an organ or tissue. When the body is irradiated, it is calculated on the organ, and when summing over the whole body, when it is uniformly irradiated, it should give 1. As a measurable analogue of these not measurable, but calculated values, it is recommended to use the amount of absorbed dose at some point of the soft tissue at a depth d = 10 mm from the surface. The quantity thus measured is called the equivalent of the individual dose, is designated Hp (10) and is indicated in Sv. For skin Hp (0,07) d = 0,07 mm and, accordingly, should be measured by a very thin detector. If the absorbed radiation dose of penetrating radiation (gamma, x-ray ≥200 keV) is measured by, for example, a LiF-based detector or an air-equivalent chamber, the dose in muscle tissue will be measured correctly, and the bone dose is 3-fold lower. To adequately measure the dose in bone tissue, a bone equivalent monitor should be used, the togle it will be measured correctly, the dose in soft tissue when measured with such a detector will be overestimated. Thus, if we have a set of detectors equivalent to different tissues, the measured dose will carry complete information on the doses absorbed in each tissue, taking into account the radiation quality. If the radiation is essentially non-uniform, weakly penetrating radiation is used, then the cover layer of the detector and the detector itself for adequate control should be comparable in thickness to the layer of radiation penetration into this tissue.

In my opinion, the medical assessment of the impact of AI is a terrible mess.

The physical quantity dose of ionizing radiation (D) is given in J/kg = Gy (Gray) and corresponds to the part of the energy transferred to a certain volume of material of mass m, D=dE/dm (Gy).

For radiological protection, weight factors were adopted which are different for each type of organ or Human tissue, since each organ has different sensitivity to the ionizing radiation type.

Thus, the dose, under radiological protection, is termed differently as equivalent dose H (Sv), where Sv = Sievert, although the unit is the same (J/kg).

All details can be found in the ICRP documents.

Если корректно измеряется поглощенная доза в материале (например, в разных тканях человека тканеэквивалентными детекторами) то никаких взвешивающих коэффициентов применять не надо. Важно чем и как ее корректно измерить. Практически в качестве детекторов излучения применяются ионизационные (газонаполненные - воздухоэквивалентные) датчики, сцинтилляционные детекторы (чаще всего с большим Z эфф, термолюминесцентные детекторы (по крайней мере, для персонала) с Z эфф которые в зависимости от применяемого материала детектора можно привести к Z эфф облучаемому материала (например мышечной ткани).

Если измерение проводиться воздухо эквивалентным детектором и измеряется фотонное излучение, то измеряемая величина это экспозиционная доза, выведенная из обращения (но хорошо измеряемая величина) ее следует приводить в рентгенах.

В настоящее время для косвенно ионизирующего излучения, включающего фотонное и нейтроны введено понятие керма. Единицы измерения: 1Гр = 1Дж/кг, это керма, при которой суммарная первоначальная кинетическая энергии всех заряженных ионизирующих частиц, образовавшихся под действием косвенно ионизирующего излучения в элементарном объеме в массе вещества в 1 кг, равна 1 Дж. Для фотонного излучения в воздухе она является энергетическим эквивалентом экспозиционной дозы.

Керма не включает в себя потери на тормозное излучение g=Kт/K. Для легких материалов (воздух) и для средних энергий g мало, для сред с большим Z, g может быть значительным. Если потерями на тормозное излучение можно пренебречь в условиях электронного равновесия для воздуха K=X~D. Таким образом, для кермы важно, каким детектором проводиться измерение и насколько велики, могут быть потери на тормозное излучение.

Поглощённую энергию в некотором объёме, содержащем вещество массой m, можно представить в виде разности энергии всех частиц, входящих в данный объём и энергия всех частиц, выходящих из него. Формирование поглощенной дозы в объекте обусловлено: ослаблением первичного пучка; увеличением за счет вторичных частиц из переднего слоя облучения. Поглощённая доза в общем случае неравномерно распределена в веществе. Доза максимальна для разных типов излучения на разных глубинах в материале. Чтобы обеспечить поглощенную дозу в органе на одинаковой глубине разными типами ИИ дозы на поверхности тела будут существенно разными.

Степень воздействия принято характеризовать мах дозой, которая будет формироваться при проникающем излучении в костной ткани. Важнейшим параметров характеризующим взаимодействие с веществом являются удельные потери энергии за счет ионизации и возбуждения атомов в-ва на единице пути dE/dх, на практике линейная передача энергии ЛПЭ (keV/mkm). Величина ЛПЭ имеет важное значение в радиационной защите, так как определяет использование разных коэффициентов качества радиационного поля.

Если использовать абсолютно тканеэксивалентные и миниатюрные детекторы, то доза в любом материале может быть определена в данной точке абсолютно точно. Для этого при измерении разных видов излучения необходимо использование тканеэквивалентного фантома и набора тканеэквивалентных ( с разными Z эфф под разные ткани) очень маленьких детекторов. Это позволило бы провести полную дозиметрию воздействие смешанного (любого типа) излучения на организм. Измеренная таким образом поглощенная доза в определенной ткани (месте фантома) при этом будет соответствовать полностью той расчетной эквивалентной дозе которую рекомендуется приводить в Sv. Расчет в Sv эффективной эквивалентной дозы для ткани тогда это только учет вклада данной ткани в общую массу человека и суммирование вкладов всех органов, чтобы получить нагрузку на все тело, т.к. качество излучения (тип излучения) полностью учитывается при измерении поглощенной дозы тканеэквивалентными детекторами.

Таким образом, разработка термолюминесцентных детекторов с разными Z эфф имитирующими разные ткани человека позволила бы полностью адекватно измерять дозы воздействия ИИ (поглощенные дозы) на человека.

Sv является (так вводится эта величина) при определения эквивалентных и эффективных доз полностью расчетной величиной.

In a simple words

The gray (Gy) is the unit of absorbed dose and

1 Gy = 1J/Kg

But when speak about the biological effect of the radiation on the body changes according to the radiation type. .we use the equivalent dose to consider the danger of different radaitions.

the equivalent dose in the in (Sv) = the absorbed dose in (Gy) x the specific type of radiation

the equivalent dose in the in (rem) = the absorbed dose in (Rad) x the specific type of radiation

....and the Unit of Kerma (transferred kinetic energy).

Sievert (Sv)

This unit is used for assessing how much risk radiation poses to people in terms of

inducing cancer or genetic damage. (1 Sievert = 1,000 mSv)

Gray (Gy)

This unit represents how much energy was received by an object or person hit by radiation. A dose of 1 gray corresponds to 1 joule of energy absorbed by 1 kilogram of matter.

In addition to @Jumah Aswad Zarnan:

The gray (Gy) is the unit of absorbed dose (energy absorbed per unit mass) while the sievert (Sv) is the unit equivalent dose. The equivalent dose is determined from the absorbed by applying a weighting factor which takes into account the quality of radiation (type and energy of ionising radiation) since the probability of stochastic effect is found to depend not only on the absorbed dose, but also on the TYPE and ENERGY of the radiation.

1 Sv = 1 Gy • wr• wt (where Sv=sievert, Gy=gray, wr=weighting factor specific to each type of radiation and wt=weighting factor specific toeach type of tissue).

Please read the question and some of the previous answers. The question concerns how to use the units in practice.

I agree with Usha Yadav Gy is measured while Sv is calculated. The instruments that measured the dose in Sv measure the Gy first and then converted into Sv by calculation.

The term of gray (Gy) know-as the unit of absorbed dose (energy absorbed per unit mass) yet the sievert (Sv) is the unit equivalent dose.

Gray is the Unit of radiation absorbed dose , 1Gy = 1J/Kg = 100Rad .

Sievert is unit of equivalent dose (H), 1Sv =100 rem .

Nada

Nice handout. This does not answer the question posed. See question and some of the earlier answers. The answers to interpretation and use of the terms may be useful for supplementing your handout.

I agree with previous answers

Most of them are great answers. I prefer the following answer:

Gray is the unit of radiation absorbed dose , 1Gy = 1J/Kg = 100Rad .

Sievert is unit of equivalent dose (H), 1Sv =100 rem

Exposure and Dose Rate. The concentration of U-238 and Th-232 in ppm and K-40 in percent (%) was used to estimate the dose rate in (nGy/h) as the following relation (IAEA- TECDOC-1363. 2003). Dose Rate (nGy/h) = 5.675 U (ppm) + 2.494 Th (ppm) + 13.078 K (%) Where 5.675, 2.494 and 13.078 are the conversion factors for U, Th and K, respectively.

To estimate annual effective doses, account must be taken of the convergent coefficient from absorbed dose in air to effective dose. The average numerical values of those parameters vary with the age of the population and the climate at the location considered. In the UNSCEAR 1993 Report, the committee used 0.7 Sv Gy-1 for the conversion coefficient from absorbed dose in air to effective dose received by adults. The occupancy factors of time spent outdoors is 0.2. So, the annual effective dose for outdoor occupancy is determined as follows: Annual Effective Dose (mSva-1 ) = Dose (nGy h-1) x 8760 h x 0.2 x 0.7 Sv Gy-1 x 10 -6

Exposure and Dose Rate. The concentration of U-238 and Th-232 in ppm and K-40 in percent (%) was used to estimate the dose rate in (nGy/h) as the following relation (IAEA- TECDOC-1363. 2003). Dose Rate (nGy/h) = 5.675 U (ppm) + 2.494 Th (ppm) + 13.078 K (%) Where 5.675, 2.494 and 13.078 are the conversion factors for U, Th and K, respectively. To estimate annual effective doses, account must be taken of the convergent coefficient from absorbed dose in air to effective dose. The average numerical values of those parameters vary with the age of the population and the climate at the location considered. In the UNSCEAR 1993 Report, the committee used 0.7 Sv Gy-1 for the conversion coefficient from absorbed dose in air to effective dose received by adults. The occupancy factors of time spent outdoors is 0.2. So, the annual effective dose for outdoor occupancy is determined as follows: Annual Effective Dose (mSva-1 ) = Dose (nGy h-1) x 8760 h x 0.2 x 0.7 Sv Gy-1 x 10 -6

follow...... .

I agree with Nada Farhan Kadhim and I recommended the following answer:

Gray is the Unit of radiation absorbed dose , 1Gy = 1J/Kg = 100Rad .

Sievert is unit of equivalent dose (H), 1Sv =100 rem .

Jorge Costa-de-Moura

Not correct. Not even close.

Read the previous answers.

Jorge

You stated that the gray is the total available energy and then, you proffer the definition

The absorbed dose characterized the amount of damage done to the matter (especially living tissues) by ionizing radiation. The absorbed dose is more closely related to the amount of energy deposited.

The SI unit of absorbed dose is the gray (Gy), which is equal to J/kg. 1 gray represents the amount of radiation required to deposit 1 joule of energy in 1 kilogram of any kind of matter.

The definition of the gray is absorbed dose, not the total available energy The gray is your 3 bullets, not the 10 available bullets.

Your definition of sievert

The sievert (Sv) is the International System of Units (SI) derived unit of equivalent radiation dose, effective dose, and committed dose. One sievert is the amount of radiation necessary to produce the same effect on living tissue as one gray of high-penetration x-rays. Quantities that are measured in sieverts are designed to represent the biological effects of ionizing radiation.

The definition of sievert is the biological effects of ionizing radiation, not the absorbed dose. The sievert could equal the 3 bullets, 2.5 bullets, or 20 bullets, depending on the biological effect of the absorbed dose.

I suggest you read my chapter "Measurement of Effective Dose" available on RG. I will gladly discuss the definitions and concepts. The reason for the original question was to determine what radiation professionals understood about the definitions and use of the units. There is much confusion within the profession as you will see if you follow the discussion.

Jorge

Your initial answer was

• “I make an analogy.
• Suppose you have 10 bullets to shoot a target.
• Every time you shoot those 10 bullets only 3 times you reach the target.
• If you use a bigger bullet or a bigger target your chances increase and, let's again suppose, you fix the bullets size and increase target and hit the target 5 times.
• if you now think that the bullets are the radiation (its size is its energy). The target's size is its area and/or its density.
• So, 10 bullets are the total available energy. That's Gray.
• 3 and 5 times (also bullets) you hit the target is the absorbed doses. Those numbers are Sievert.
• That's why I think that, once you know what Gray and Sievert mean you may use them both indistinctly.”

Do you mean that 10 bullets are absorbed, but only 3 or 5 cause biological damage? Your last answer says,

• “exactly that 10 bullets were the available "absorbed"doses and the target was the biological damage caused by the absorbed dose.”

Your first answer says

• 10 bullets are the total available energy. That's Gray.
• 3 and 5 times (also bullets) you hit the target is the absorbed doses. Those numbers are Sievert.

I understand this to mean (if available = absorbed)

• 10 bullets absorbed > Gray
• 3, 5 bullets absorbed > Sievert

How can you say, “once you know what Gray and Sievert mean you may use them both indistinctly.”

I do not understand how 10 Gy is indistinguishable from 3 or 5 Sv.

Jorge, i have big problems to follow your construct. It’s far easier to use the clear definitions of doses. Locally absorbed energy per mass is absorbed dose. If this absorption is concentrated by particles interaction, the damage is more concentrated to biological tissues or molecules. So you define factors to describe the enhanced harm by empirical factors. Then calculate the product of absorbed dose, the grays wth these factors. You get the sievert. Please no bullets and probabilities to meet the targets. Pleas read icrp 103 or my chapter.

Jorge, indeed you use dosemeters, which measure in a first step the absorbed dose at a special location in a radiation field. You get the Grays. Then to convert your dosemeter for radiation protection purposes, you have to calibrate it for the specified condition. This first calibration contains the quality factor Q or wr of the particles in your field. For photons and other low LET particles you have wr =1, for alphas wr = 20 etc. You now get the Sv.The second part of the calibration converts your point dose at a location in the radiation field to a personal dose for radiation protection by exposing your dosemeter to enlarged and directed fields in a specialized labaratory. You need this additional calibration to measure the correct exposuree of persons.

Conclusion: you get the Sv by calibrating an absorbed dose detector with special factors and the realistic conditions in the radiation fields.

For gamma exposure the quantity of Gy is equal Sv generally for purposes of therapy and calibration (energy absorption )J/kg

We use Sv quantity to refer to the value of damage

Fadhil Mizban

It is not proper to use Sv for therapy. Sv refers to low dose and dose rate, only. Sv is an estimate of cancer risk.

In my country (Spain) absorbed dose is used for radiation protection purposes when applied to a direct measurement, for example when you report the dose rate at 1 m from a metabolic therapy patient. Effective dose is used when you want to take into account other factors, such as "use factors" and the like to convert a direct measurement to a stimate of personal dose.

SV radiation unit used in low doses (as in biological effects)

and GY radiation unit used in high doses ( such as in material effects as in radiation effects in electronic devices and systems)

There appears to be some confusion between a quantity and its units. I will keep my definitions relevant to macroscopic absorbers (i.e. not microdosimetry)

The Gy unit applies to the quantity Absorbed Dose and it is purely physical. The unit is equal to the average energy absorbed per unit macroscopic mass of any absorber (1 Gy = 1 J/kg). It can be computed or measured with a calibrated dosimeters.

On the other hand, the Sv unit is used in a variety of bio-quantities to estimate the "biological impact" of a radiation exposure. Its determination requires a biological assay, in addition to a calibrated physical dosimeter system.

The Sv unit is used for Equivalent Dose (Sv) that accounts for the biological effects (e.g. DNA breaks) from different types of radiation with different Linear Energy Transfer (LET, e.g. protons versus x-rays). The absorbed dose is multiplied by a radiation quality weighting factor (usually greater than 1.0, relative to ordinary x-rays). Equivalent Dose (in units of Sv) is therefore generally not equal numerically to Absorbed Dose (in units of Gy).

The Sv unit is also used for a "whole body" quantity - Effective Dose (Sv) whereby Equivalent Doses in each tissue compartment are weighted by their sensitivity (e.g. for cancer induction at lower dose or acute effects at higher dose) and summed over all exposed tissue.

Unfortunately, the radiation literature is very sloppy in its use of units, often mixing up physical and biological quantities of "dose". The international standards and definitions can be found here:

https://www.icru.org/journal-of-the-icru/uncategorised/journal-of-the-icru

Good contribution &Jerry, but a small error. Acute or chronically tissue effects are never described by Sv, because you have no factors to take into account the tissue sensitivity For deterministic tissue reactions. The factors wt are only used for stochastic effects.

Regards.

Thanks Hanno for this comment. I offer the following clarification to my incorrect statement.

The Effective Dose (in Sv) is indeed used most often for comparing stochastic (cancer and hereditary) effects from whole/partial body low exposures at low dose rate. For example, natural background radiation and medical radiation exposures are often compared in this way for risk assessment.

As far as deterministic effects from larger doses delivered acutely, the Equivalent Dose to organs at risk is applicable and the units remain in Sieverts.

As mentioned in my conclusion, one must be very careful to state what type of "dose" is under considerations. I was perhaps a bit sloppy myself !

Jerry I never would use Sv to describe effects. I would inform about the beam or radiation quality and present the Gray. The rest is knowledgeable of the listener or reader.

Hanno...

I guess we must simply disagree on the concept of Equivalent Dose (sometimes called Dose Equivalent) in Sv.

How would you assess the acute effect form an absorbed dose delivered only to a body organ by a non-x-ray beam with higher LET?

Equivalent Dose (Sv) = Absorbed Dose (Gy) x Radiation Weighting Factor.

This is not necessarily an organ-specific concept, but it is a better estimate of biological impact since the radiation weighting factor is obtained from a biological assay ( e.g. DNA breaks, cell survival).

A typical example. We offer 2.1 Gy for therapy in oncology with protons per day. It’s very easy. That means we take care for the let.

According to ICRP, Task Group79 Draft

"The control of stochastic effects relies almost entirely on the use of effective dose. To  the extent that it is necessary to consider organ and tissue doses, they are better expressed in terms of absorbed dose in gray (Gy), avoiding any potential confusion with effective dose In sievert (Sv). "

Thank you Joseph and Hanno.

What I am hearing from Joseph is that the concept of Equivalent Dose (Sv) will be (and should now be) abandoned to avoid the "units and concepts confusion" such as what we are debating here today!

Hanno...As far as the dose per fraction used in radiation oncology ( e.g. 2.1 Gy per fraction for proton beams) it is the standard x-ray dose fraction multiplied by a proton weighting factor. This weighting factor reflects the higher LET indeed but it does have a "radiobiological" flavour. It has been inferred from biological assays ( e.g. cells exposed to protons versus x-rays). According to traditional books ( e.g. Eric Hall's Radiobiology for the Radiologist) this "was" an Equivalent Dose of 2.1 Sv but the modern implementation has abandoned the use of the ambiguous Sv. Oncologists and medical physicists in this field have opted to consistently use the Gy only in dose prescriptions, avoiding ambiguity with the Effective Dose (Sv).

I now understand the "historical" nature of our disagreement.

Here is a concluding summary that I hope harmonizes all of our points of view:

Gy units for Absorbed Dose and Equivalent Dose (with radiation weighting)

Generally applies to acute delivery at high dose rate and large total doses.

Example - radiological accidents, radiotherapy;

predictive of deterministic effects on organs at risk (and tumours)

Sv units for Effective Dose (with tissue weighting for stochastic effects)

Generally applies to chronic delivery at low dose rates and low total doses

Example - Background radiation level, diagnostic imaging doses;

predictive of stochastic risks (cancer induction and/or hereditary effects).

Thanks Jerry,

thats exactly my point of view. And really no problem to have such high level discussions.

Hanno - this discussion was very good and we are now "up to date" and consistent. Joseph - I was not aware of the recent ICRP Report 79 Draft. I will check with the ICRU also and see if they have abandoned the Sv unit for Equivalent Dose and use Gy instead. Best Regards to both of you.

Now back to Mother's Day activities .

I regret to re-open this thread of discussion once again.

From the ICRP 79 Draft Report:

"Although equivalent dose can and currently is used to specify limits relating to tissue reactions, absorbed dose (Gy) is the preferable quantity, drawing a clear distinction between limits applying to tissue reactions, set in absorbed dose (Gy), and those applying to stochastic effects, set in effective dose (Sv)... However, exposures to neutron and other high LET radiations may require consideration... it may then be necessary to take account of increased effectiveness per Gy (ICRP, 1990, 2003b)." ....

"Equivalent dose can be seen as an intermediate step in the calculation of effective dose. Dose limits, dose constraints and reference levels in relation to stochastic health effects are set in terms of effective dose. Equivalent dose has been used to specify limits for the avoidance of tissue reactions but, these will be more appropriately set in terms of absorbed dose (Gy). Communication difficulties have arisen in situations where equivalent dose and effective dose expressed in the same units (Sv) have not been adequately distinguished."

As far as I know, final ICRU/NCRP/ICRP Reports have never expressed Equivalent Dose in Gy units. Until that happens officially, deterministic doses (legal limits or radiotherapy prescriptions) are in theory Equivalent Dose (Sv) = Absorbed Dose (Gy) x radiation weighting factor. The radiation oncology community chooses to use "Gy" instead for practical reasons - avoiding clinical confusion between Gy and Sv in the treatment chart or at the therapy machine, when using high LET beams (e.g. protons, heavy ions)

To recap, we are 100% in agreement on the concept of Equivalent Dose (or Dose Equivalent) for high-LET exposures. What we are debating is what is the most appropriate Unit Name ! The preference depends on whether one wears a medical physics, health physics, radiobiology, or clinical hat!

Jerry J Battista

Discuss, please. The ICRP 79 Draft Report goes a long way toward clearing the confusion about Sv and Gy. Unfortunately, it is a draft (do not cite or quote) and being the product of a committee it has to equivocate. When is a spade a spade, before or after the chicken hatches?

Sv is a term of risk. It is for radiation protection purposes. It applies to low dose and low dose rate stochastic effects.

Please refocus on the original question: What is the difference between Sievert and Gray? The answer is that they are both radiation units that share the same fundamental SI base (J/kg), but they are used for different quantities in medical physics, radiation protection, and radiation oncology.

We agree 100% that the Absorbed Dose quantity is expressed in units of Gy and Effective Dose quantity is expressed in units of Sv. The only debate remains on what is the best unit to use for the Equivalent Dose quantity, used for deterministic (non-stochastic) effects on tissue and organs, accounting for the RBE(LET) of the radiation exposure.

To my knowledge , the Sievert (Sv) remains as the official unit for Equivalent Doses according to ICRP/NCRP/ICRU Reports, but in practical radiation oncology, this convention is ignored ( e.g. proton therapy). The Gray is used for universal dose prescriptions and normal tissue tolerance limits but the "Grays" are indeed corrected for the RBE (LET) of the treatment beam. Note that this is entirely consistent with the concept of Equivalent Dose but it "switches" the unit to Grays for clinical convention and safety reasons.

If you find an official definition of Equivalent Dose in units of Grays from any updated published Reports, I would be delighted to change my opinion on this matter where we seem to be going in endless circles.

I offer an interpretation of Hanno's dose prescription of 2.1 Gy (per proton treatment fraction). This is actually an equivalent x-ray dose producing the same cell killing effect as an absorbed proton dose of 2.0 Gy. I attach a rough sketch that shows the Absorbed Dose (Gy) and Equivalent x-ray Dose (in Sv according to ICRU convention) with an assumed RBE of 1.05. If you force Gy units for all types of radiation, then your must specify that these are actually x-ray dose equivalents. I hope this resolves our different points of view. It was a great discussion !

One final word of caution...the RBE changes its value along the Bragg curve.

Yes Jerry, and the highest LET will be found around the Bragg peak. And in this energy region the dose equivalent of 2.1 Gy arises.

I can see why an x-ray based dose prescription is useful in radiation oncology because most of our human clinical experience is based on x-ray dose levels with vanilla-flavoured low-LET radiation.

I am attaching a Summary Table that I published on High-LET radiation in space (to Mars and back). You will see the Gray-Eq Dose (Gy) quantity which is in fact exactly what you are using in place of Equivalent Dose (H) !

I should have spotted this sooner in our discussion. The attached Table is a nice way to end this thread, if Joseph agrees.

Jerry J Battista

You said

"Please refocus on the original question: What is the difference between Sievert and Gray? "

Glad to. Please read the entire question. The question regards practical definitions and usage.

You concluded

"If you find an official definition of Equivalent Dose in units of Grays from any updated published Reports, I would be delighted to change my opinion on this matter where we seem to be going in endless circles."

Nothing I said was intended to be confrontational.

There are many confusions in using Sv and Gy. ICRU/NCRP/ICRP defined Sv and Gy for radiation protection purposes at low doses.

From the ICRU website

Several milestones can be identified in the development of concepts, quantities and units for dosimetry in radiation protection:

- in 1953, at the 7th International Congress of Radiology in Copenhagen, the ICRU introduced the absorbed dose in irradiated material, by any type of ionizing radiation, as the fundamental quantity correlated to the induced biological effect. The special unit introduced was the rad; now this special unit in the "Système International" (SI) is the gray (Gy).

- in 1962, the ICRU introduced -for radiation protection purposes- the quantity dose equivalent as a product of the absorbed dose and various modifying factors, the most important of which is the quality factor. This factor accounts for differences in the relative biological effectiveness of different types of ionizing radiations at low doses. The special unit introduced was the rem; now the SI-based special unit is the sievert (Sv).

- in 1977, the ICRP introduced (ICRP Report 26) the effective dose equivalent, based on the dose equivalent in various organs of an individual and the weighted sum of these, as a limiting quantity for all types of exposure. In 1991, the ICRP modified its approach and introduced effective dose.

-in 1985, the ICRU (ICRU Report 39) introduced operational quantities for the specification of dose equivalent, for area and individual monitoring in the case of external radiation sources.

I cannot find a reference for effective or equivalent dose for medical purposes. If your institution uses Sv for medical doses, that is just the information the question was looking for. If you want to justify that use, go ahead.

Sv is for radiation protection purposes at low doses and dose rates. It is defined as such by ICRU and ICRP as such. It is defined for stochastic risk, not deterministic effects.