The terms “relative biological effectiveness” (RBE) and “linear energy transfer” (LET) were coined in 1931 and 1952, respectively.

G. Failla, P. Henshaw, The relative biological effectiveness of x rays and gamma rays, Radiology 17 (1) (1931) 1–43.

R.E. Zirkle, D.F. Marchbank, K.D. Kuck, Exponential and sigmoid survival curves resulting from alpha and X-irradiation of Aspergillus spores, J. Cell. Comp. Physiol. 39 (Suppl. 1) (1952) 75–85.

RBE is used to compare the effectiveness of the type of radiation of the interest with that of a reference radiation. LET is the average amount of radiation energy deposited per unit length, which is usually expressed in keV/µm. Low-LET radiation includes photons (i.e., X-rays and gamma-rays) which are sparsely ionizing radiation. High-LET radiation includes alpha particles, heavy ions or neutrons, which are densely ionizing radiation. Radiation with LET of >10 keV/µm is some times referred to as high-LET radiation.

For instance, RBE is calculated as the 10% clonogenic survival dose (D10) for high-LET radiation (serving as the radiation of interest) divided by that for low-LET radiation (serving as a reference radiation).

RBE greatly varies with a variety of factors, such as the choice of a reference radiation, LET, dose, dose per fraction, dose rate, end points, and tissues/organs. Therefore, care should be taken when RBE values from the different experimental system or conditions need to be compared.

As regards the choice of a reference radiation, low energy photons have higher RBE (e.g., two or three fold) than high-energy photons. As regards the LET, RBE increases up to 100 or 200 keV/µm depending on ion species, and then decreases (even to less than unity, e.g., at 1000 keV/µm, due to “over kill”). RBE generally increases with decreasing dose, dose per fraction, and dose rate to a presumed maximum value.

Provided below are some of our pertinent papers

https://www.researchgate.net/publication/23303300_Recent_Insights_into_the_Biological_Action_of_Heavy-Ion_Radiation

https://www.researchgate.net/publication/45461878_Recent_Advances_in_the_Biology_of_Heavy-Ion_Cancer_Therapy

https://www.researchgate.net/publication/6975395_LET-Dependent_Survival_of_Irradiated_Normal_Human_Fibroblasts_and_Their_Descendents

https://www.researchgate.net/publication/6975400_Histone_H2AX_Phosphorylation_in_Normal_Human_Cells_Irradiated_with_Focused_Ultrasoft_X_Rays_Evidence_for_Chromatin_Movement_during_Repair

https://www.researchgate.net/publication/307560584_Cataractogenesis_following_high-LET_radiation_exposure

Article Recent Insights into the Biological Action of Heavy-Ion Radiation

Article Recent Advances in the Biology of Heavy-Ion Cancer Therapy

Article LET-Dependent Survival of Irradiated Normal Human Fibroblast...

Article Histone H2AX Phosphorylation in Normal Human Cells Irradiate...

Article Cataractogenesis following high-LET radiation exposure

Thank You So Much!!!

My pleasure, Dr Shrikant Patil

RBE-weighted absorbed dose is used both in radiation therapy and in radiation protection.

For radiation therapy, RBE-weighted dose is called biological dose, e.g., Gy equivalent (GyE). The information on the GyE system for carbon ion therapy at HIMAC of NIRS is available at

https://www.ncbi.nlm.nih.gov/pubmed/16414376

For radiation protection, various radiation weighting factors have/had been used: RBE, quality factor (QF or Q), dose distribution factor, and/or other necessary modifying factors, and wR.

Historically, relative biological efficiency or relative biological effectiveness was used in 1950–1964 in the recommendations of the International Commission on Radiological Protection (ICRP) as a radiation weighting factor, which was changed to quality factor or wR.

Currently, wR (factor for stochastic effects) is used to compute effective dose and equivalent dose both in Sv. RBE-weighted dose is called Gy(RBE), RBE-D, Gy-Eq, etc, which are used for tissue reactions (formerly called nonstochastic or deterministic effects).

The US National Council on Radiation Protection and Measurements (NCRP) has changed equivalent dose limit for the lens of the eye, skin and extremities to absorbed dose limit with the use of RBE. ICRP Task Group 79 is proposing the withdrawal of equivalent dose limit for tissue reactions. The International Commission on Radiation Units and Measurements (ICRU) is proposing a change in operational quantity for the lens of the eye from Sv to Gy. RBE (especially for tissue reactions) is thus becoming more important.

The information on the historical development of RBE values or related weighting factors used in ICRP recommendations is available in the following paper, especially you may be interested in Supplementary Tables 2 and 3

https://www.researchgate.net/publication/262054513_Classification_of_radiation_effects_for_dose_limitation_purposes_History_current_situation_and_future_prospects

Article Classification of radiation effects for dose limitation purp...

In Japanese atomic bomb survivor studies, a constant RBE of 10 has currently been used for neutrons, but previously it was as a function of dose in the tentative 1965 dose estimates revised (T65DR) and the dosimetry system 1986 (DS86). From the cataract viewpoints, the related information is available in the left column on page 269 in the following paper

https://www.researchgate.net/publication/307560584_Cataractogenesis_following_high-LET_radiation_exposure

Article Cataractogenesis following high-LET radiation exposure

Thank You So Much Sir!!!

For workers (including aircrew) and the public on Earth, a radiation weighting factor (wR) is used to derive weighted doses. Equivalent dose in Sv is an absorbed dose singly weighted with wR. Effective dose in Sv is an absorbed dose double weighted with wR and tissue weighting factor (wT). wR and wT have been recommended by the International Commission on Radiological Protection (ICRP), and the same factors have been used by the US National Council on Radiation Protection and Measurements (NCRP). ICRP has recommended wR since 1990 and wT since 1977.

For astronauts in the International Space Station (ISS), the Flight Rules (defining an international joint exposure limit) and the Japan Aerospace Exploration Agency (JAXA, defining a target level) use Q(L) to calculate equivalent dose or effective dose. Q(L) is the quality factor as a function of LET recommended first in ICRP Publication 60 in 1990.

The US National Aeronautics and Space Administration (NASA) uses the relative biological effectiveness (RBE) to calculate gray equivalent (Gy-Eq). RBE values commonly recommended for the lens of the eye, skin, blood forming organs, and circulatory systems are 6.0 in a range between 4 and 8 for 1–5 MeV neutrons, 3.5 (2-5) for 5-50 MeV neutrons, 2.5 (1-4) for heavy ions, and 1.5 for >2 MeV protons. There have not been sufficient data for 25 MeV neutrons and heavy ions (Z >18) to derive RBE. RBE for late tissue reactions is higher than that for early tissue reactions in some tissues.

These NASA’s RBE values are based on Table 6.4 of NCRP Report No. 132 “Radiation Protection Guidance for Activities in Low-Earth Orbit” in 2000 ( https://www.ncrppublications.org/Reports/132  ). RBE values recommended in Table 6.4 of NCRP Report No. 132 are based on ICRP Publication 58 “RBE for Deterministic Effects” in 1990 ( http://www.icrp.org/publication.asp?id=ICRP%20Publication%2058  ).

NCRP Report No. 116 “Limitation of Exposure to Ionizing Radiation” in 1993 (http://ncrponline.org/publications/reports/ncrp-reports-116/  ) is NCRP’s latest basic/general recommendations, of which update has been made by Council Committee 1 (CC 1). The CC 1 draft was subjected to public consultation on 22 June 2017 to 24 July 2017. Publication of the new recommendations superseding NCRP Report No. 116 is expected in 2018. Various changes are expected. Of these, equivalent dose limits for deterministic effects will be changed to absorbed dose limits for tissue reactions along with the use of RBE values recommended in Table 6.4 of NCRP Report No. 132. Such changes are based on NCRP Reports No. 106 “Limit for Exposure to “Hot Particles” on the Skin” in 1989 (http://ncrponline.org/publications/reports/ncrp-reports-106/  ), No. 116  “Limitation of Exposure to Ionizing Radiation” in 1993 (http://ncrponline.org/publications/reports/ncrp-reports-116/  ) and No. 130 “Biological Effects and Exposure Limits for “Hot Particles” ” in 1990 (http://ncrponline.org/publications/reports/ncrp-reports-130/  ) for skin and extremities, and on NCRP Commentary No. 26 “Guidance on Radiation Dose Limits for the Lens of the Eye” in 2017 for the lens of the eye (https://www.ncrppublications.org/Commentaries/26  ).

The following paper gives brief overviews of NCRP Commentary No. 26

[In press] https://www.researchgate.net/publication/314245875_Guidance_on_radiation_dose_limits_for_the_lens_of_the_eye_overview_of_the_recommendations_in_NCRP_Commentary_No_26

[Published in July 2017] https://www.researchgate.net/publication/317240022_National_Council_on_Radiation_Protection_and_Measurements_Commentary_Number_26_Impact_of_Revised_Guidance_on_Radiation_Protection_for_the_Lens_of_the_Eye

[Published in June 2017] https://www.researchgate.net/publication/314079779_Outline_of_NCRP_Commentary_No_26_Guidance_on_radiation_dose_limits_for_the_lens_of_the_eye

[Published in February 2016] https://www.researchgate.net/publication/288829991_Status_of_NCRP_Scientific_Committee_1-23_Commentary_on_Guidance_on_Radiation_Dose_Limits_for_the_Lens_of_the_Eye

Article Guidance on radiation dose limits for the lens of the eye: o...

Article National Council on Radiation Protection and Measurements Co...

Article Outline of NCRP Commentary No. 26 “Guidance on radiation dos...

Article Status of NCRP Scientific Committee 1-23 Commentary on Guida...

You may also be interested in the following questions and answers.

https://www.researchgate.net/post/Radiation_Weighting_Factors2

https://www.researchgate.net/post/Can_any_one_explain_the_ICRP_dose_limits_radiation_weighting_factors_and_tissue_weighting_factors?

Thank You So Much Sir!!!

My pleasure, Dr Shrikant Patil