I have measured Counts from a γ-counter for different organs (lungs, liver, spleen, stomach, brain, kidney and heart) after 3.5 hours of intravenous injection with 80 MBq initial dose of Technetium labeled with Glycol Chitosan Palmitoylated quaternary ammonium (GCPQ). Now I want to convert these counts in to organ injected doses. Please can any person guide me how to do this?
What kind of counter have you used and how did you perform the organ counting exactly?
Pardon my comment, but how can you justify the application of radioactivity to a human if you don't know how to evaluate the measured data? Or was the activity applied to an animal?
Absorbed dose to an organ is defined as the energy absorbed (from radiation) divided by the mass of the organ.
In order to calculate the energy absorbed in an organ, you need to know the total activity of the pharmaceutical in that organ and such quantity is time dependent.
You need some information such as the bio-kinetic model (biologic distribution) for the animal that you have used in your experiment. You also need organ dose calculation software that will sum up all the radiation energies from all the source organs to the target organs in the animal under study.
The most common software is known as OLINDA (organ level internal dose assessment) written by Dr. Michael Stabin, of Vanderbilt University; but this software is applied to human data and not to animal data as far as I know! But you can check out the software applications available online. I guess you may be able to benefit from the software phantom results by using the following relation
A (phantom) = A(animal) [( m/Mphantom) /(m/Manimal)] where m is the organ mass and M the total body mass.
using the animal organs mass to obtain an approximation of the doses to the organs; anyway what is done is usually an estimate of the organ dose; do not forget that an estimate has always an associated uncertainty.
To convert the measured counts in each organ to an activity in (Bq) deposed into the organ; you need to calculate a factor relating the counts registered by the gamma counter used and the corresponding standard radiation source (radiopharmaceutical) activity in (Bq). Then once you have the determined the activity you need another factor that will relate the integrated Activity in time measured in (Bq.hr) to the absorbed dose in (rads) and this is what is missing the so called (S) factor. You need the software for that because (the software uses Monte Carlo simulations results and mathematical phantoms).
Good luck
why not use quantitative small animal SPECT?
Article Effects of attenuation map accuracy on attenuation-corrected...
this is the paper that explains how it works. System and software available via MIlabs
Article Quantitative multi-pinhole small-animal SPECT: Uniform versu...
So far I know such facility does not exists at your University. Perhaps you are are doing it somewhere else. I think Khalid Soliman has right solution to your problem.
Dear All
I am really thankful to all of you for your prestigious comments that were very helpful in setting further directions to me.
I have also found a research paper by Mr. Daryoush Shahbazi-Gahrouei and co-researchers. That was also useful.
J Med Signals Sens. 2012 Oct-Dec; 2(4): 231–234.
PMCID: PMC3662107
Daryoush Shahbazi-Gahrouei, Mohsen Cheki,1 and Masoud Moslehi
Author information ► Article notes ► Copyright and License information ►
Abstract
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INTRODUCTION
A bone scan or bone scintigraphy is a nuclear scanning test to find certain abnormalities in bone that are triggering the bone's attempts to heal. It is primarily used to help diagnose a number of conditions relating to bones, including: Cancer of the bone or cancers that have spread (metastasized) to the bone, locating some sources of bone inflammation (e.g., bone pain such as lower back pain due to a fracture), the diagnosis of fractures that may not be visible in traditional X-ray images, and the detection of damage to bones due to certain infections and other problems.[1,2]
Accurate dosimetry for representative groups of patients for each specific investigation is needed in order to optimize use of the various alternative radiodiagnostic techniques, and to estimate the collective radiation exposure and risk from nuclear medicine investigations.[3]
A computer program called MIRDose, has been developed and distributed by M.G. Stabin, Radiation Internal Dose Information Center, Oak Ridge Institute for Science and Education, Oak Ridge, USA. The program contains tables of the S factors for the common radionuclides; the user must provide the biokinetic data in the form of residence times for the source organs. The program then generates tables of organ doses per unit administered activity in the traditional and SI units (rad/mCi and mGy/MBq).[4,5]
Internal dose of different organs can be estimated by different methods such as Medical Internal Radiation Dosimetry (MIRD). In MIRD method, the dose absorbed in the target organs are estimated as a function of activities accumulated in the source organ and it provides a generally correct mathematical estimate dose.[6–8] The aim of the present study was to compare estimation of radiation absorbed doses to patients following bone scans with technetium-99m-labeled methylene diphosphonate (MDP) with the estimates given in MIRDose software (Version 3.0. 2).
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MATERIALS AND METHODS
The study was performed on 30 adult patients (18 women and 12 men) with an average age of 38 ± 12 years referred to the nuclear medicine department of Seyed Al-shohada hospital in Isfahan, Iran for evaluation bone metastases. All patients signed a consent form after receiving detailed information about the aim of the study. Each patient was injected with 25 mCi of 99mTc-MDP. Patients were imaged with a dual-head gamma camera (Siemens GammaSonics, Hoffman Estates), equipped with low-energy collimators. A 20% energy window around the photopeak of 99mTc was used. Whole-body images from the thirty patients were acquired at 10, 60, 90, 180 minutes after 99mTc-MDP injection. Images of five min duration were acquired. To determine the activity, in different organs, conjugate view method was applied on total body images. Regions of interest (ROIs) were manually drawn on anterior and posterior images around all organs (liver, bladder wall, spleen and kidneys) on each time frame. A subtraction of surrounding activity was done by drawing ROI in neighborhood of each organ. The same set of ROIs was used for all scans and the counts in each ROI were converted to activity using the conjugate view method which illustrated by the following equation.[9–12]
In this equation, A is the organs activity in mCi, IA and IP are the anterior and posterior view background corrected counting rates, respectively, t is the body anterior–posterior thickness across each organ, this thickness were measured on the CT scanner (Brilliance; Philips). Also μe is the effective linear attenuation, f is equal to (μet/2)/sinh(μet/2) and represents a correction for the source region attenuation coefficient (μe) and source thickness (t) and C is the system calibration factor (counting rate per unit activity). The system calibration factor used in this study was obtained by counting a known activity of 99mTc for a fixed period of time in air using the same camera, collimators and the camera acquisition settings. The mean uptake activity in different time periods (10, 60, 90, 180 min) after injection of 99mTc-MDP were also calculated for each organ and used in the time–activity curves. The time–activity curves used to calculate the cumulated activity in each organ was fitted by MATLAB software (Version. 7.5).
For obtained corrected counting rate, the counting rate measured in an adjacent ROI was subtracted from the counting rate in organs ROI, in according to the formula reported by Buijs et al., equation.[9]
Where IA(IP) is the background corrected counting rate in the anterior (posterior) organs ROI, I’A(I’P) is the measured counting rate in the anterior (posterior) organs ROI and IBGA(IBGP) is the counting rate in the anterior (posterior) background ROI.
Based on the MIRD schema, absorbed doses (D) were calculated for the liver, bladder wall, spleen and kidneys using follow formula:[12–14]
D = Ã × S
where à is the cumulated activity, “S” factor obtained from Yoriyaz and co-workers study.[15] The results of this study were compared with the data of MIRDose software[16] by performing t-test.
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RESULTS
The absorbed doses per unit of injected activity (mGy/MBq × 10–4) for liver, kidneys, bladder wall and spleen were 3.86 ± 1.1, 38.73 ± 4.7, 4.16 ± 1.8 and 3.91 ± 1.3, respectively.
The results of t-test to compare the results of the data of MIRDose software and present study are shown in Table 1.
Table 1
Results of t-test to compare the data of MIRDose software with the present study
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DISCUSSION
Radiation dose calculations for radiopharmaceuticals have been standardized by implementation and dissemination of tools like MIRDose software. The MIRDose software greatly facilitates the calculation of internal radiation dose estimates by the MIRD techniques. The program makes use of standard and most up-to-date models in internal dosimetry.[16]
The accurate absorbed dose calculations depends on the accuracy of the quantifications of organ activity.[17] The accuracy of the quantifications of organ activity from planar gamma camera images has been evaluated by several researchers.[17–20] They are demonstrated factors such as the effective attenuation coefficient (which could influence the estimation of activity by about ±10%), body thickness (±10%) and device sensitivity (±5%) which influences the accuracy of activity quantification. However, researchers noted that background activity was perhaps the most important factor, with differences in how background regions were defined contributing to as much as ±20% variation of the observed activity values from the known results. Another factor to consider in quantification of the activity based on planar scintigraphy is the effect of overlapping tissue. This applies particularly to kidneys and liver.[17–20]
Table 1 shows that the P values of compared the results of this study with the data of MIRDose software is more than 0.05 which means that there is no significant differences among these. According to the results here [Table 1], the P value of liver is higher than the rest which means is more in agreement with other studies.[17–19]
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CONCLUSIONS
The results of this study showed that methods used in the study for absorbed dose calculation is in good agreement with the data of MIRDose software and it is possible to use the obtained method of the present study, by a clinician. Also findings may be useful to estimate the amount of activity that can be administered to the patients and also serve as a way of comparing the risk to the benefit value of these nuclear medical procedures with the other modalities of diagnostic procedures.
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BIOGRAPHIES
Daryoush Shahbazi-Gahrouei obtained his BSc from the Department of Science of Isfahan University in Iran in 1987, and his MSc from the School of Medical Sciences of Tarbiat Modarres University, Tehran, Iran, in 1991. He obtained his PhD in Medical Physics at the University of Western Sydney and St. George Cancer Care Centre, Sydney, Australia, in 2000. He holds the position of Professor of Medical Physics at the Department of Medical Physics and Medical Engineering in the School of Medicine of Isfahan University of Medical Sciences, Iran. He has authored many papers in the area of Medical Physics, including of novel nanoparticles as MR imaging contrast agents for cancer detection, natural radiation, nuclear medicine, medical and molecular imaging, effects of electromagnetic fields, radiation protection, advanced radiation therapy and radiation dosimetry.
E-mail: [email protected] or [email protected]
Mohsen Cheki received his BSc degree in Radiology Technology from Shahid Beheshti University of Medical Sciences in Tehran Iran, 2007 and his MSc degree from the department of Medical Physics of Isfahan University of Medical Sciences, Isfahan, Iran, 2012. Now he is a PhD student in Medical Physics at Tehran University of Medical Sciences, Tehran, Iran. His research interest is radiation dosimetry and molecular imaging.
E-mail: [email protected]
Masoud Moslehi graduated as a Medical Doctor from Isfahan University of Medical Sciences in Isfahan, Iran in 1999. He received his specialty in Nuclear Medicine from Tehran University of Medical Sciences in 2005. Currently he is assistant Professor of Nuclear Medicine in the department of Medical Physics and Medical Engineering at Isfahan University of Medical Sciences.
E-mail: [email protected]
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Footnotes
Source of Support: Nil
Conflict of Interest: None declared
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REFERENCES
1. Brown ML, Collier BD, Fogelman I. Bone scintigraphy: Part I. Oncology and infection. J Nucl Med.1993;34:2236–40. [PubMed]
2. Brown ML, O’Connor MK, Hung JC, Hyostek RJ. Technical aspects of bone scintigraphy. Radiol Clin North Am. 1993;31:721–30. [PubMed]
3. IAEA (2001)-TECDOC-1228. Therapeutic applications of radiopharmaceuticals. India: Proceedings of an International Seminar held in Hyderabad; 1999. pp. 18–22.
4. Stabin MG, Flux GD. Internal dosimetry as a tool for radiation protection of the patient in nuclear medicine. Biomed Imaging Interv J. 2007;3:e28.
5. Fleming JS. A technique for the absolute measurement of activity using a gamma camera and computer. Phys Med Biol. 1979;24:176–80. [PubMed]
6. Stabin MG. MIRDOSE: Personel computer software for internal dose assessment in nuclear medicine.J Nucl Med. 1996;37:538–46. [PubMed]
7. Shahbazi-Gahrouei D, Nikzad S, Shokrani P, Shahi Z, Monadi SH. Determination of absorbed dose of organs (Thyroid, Sternum, Cervical vertebra) in thyroid cancer patients following radioiodine therapy.Iranian J Nucl Med. 2009;17:27–33.
8. Shahbazi-Gahrouei D, Nikzad S. Determination of organ doses in radioiodine therapy using medical internal radiation dosimetry (MIRD) method. Iranian J Radiat Res. 2011;8:249–52.
9. Buijs W, Siegel JA, Boerman OC, Corstens FH. Absolute organ activity estimated by five different methods of background correction. J Nucl Med. 1998;39:2167–72. [PubMed]
10. Siegel JA, Thomas SR, Stubbs JB, Stubbs JB, Stabin MG, Hays MT, et al. MIRD pamphlet no. 16: Techniques for quantitative radiopharmaceutical biodistribution data acquisition and analysis for use in human radiation dose estimates. J Nucl Med. 1999;40:37–61. [PubMed]
11. Vazques AG, Flores GF, Murphy CA, Garcia ZG. Biokinetics and dosimetry in patients of 99mTc-EDDA/HYNIC-Tyr3-octreotide prepared from lyophilized kits. J Radiat Isot. 2006;57:792–7. [PubMed]
12. Bin L, Anren K, Rui H, Zhen Z, Zang Y, Jiantao W, et al. Influence of vitamin c on salivary absorbed dose of 131I in thyroid cancer patients: A prospective, randomized, single-blind, Controlled trial. J Nucl Med. 2010;51:618–23. [PubMed]
13. Harris CC, Greer KL, Jaszczak RJ, Floyd CE, Fearnow EC, Coleman RE. Tc-99m attenuation coefficients in water-filled phantoms determined with gamma cameras. Med Phys. 1984;11:681–5.[PubMed]
14. Jentzen W, Schneider E, Freudenberg L, Eising EG, Gorges R, Muller SP, Brandau W, et al. Relationship between cumulated radiation dose and salivary gland uptake associated with radioiodine therapy of thyroid cancer. Nucl Med Commun. 2006;27:669–76. [PubMed]
15. Yoriyaz H, Stabin MG, dos Santos A. Monte Carlo MCNP-4B-based absorbed dose distribution estimates for patient-specific dosimetry. J Nucl Med. 2001;42:662–9. [PubMed]
16. Helal N. Patient organs dose calculations in nuclear medicine. Int J Res Rev Appl Sci. 2012;11:153–61.
17. Norrgren K, Svegborn SL, Areberg J, Mattsson S. Accuracy of the quantification of organ activity from planar gamma camera images. Cancer Biother Radiopharm. 2003;18:125–31. [PubMed]
18. Jaszczak J, Coleman E, Whitehead R. Physical factors affecting quantitative measurements using camera-based single photon emission computed tomography (SPECT) IEEE Trans Nucl Sci.1981;28:69–80.
19. Stabin M. Uncertainties in internal dose calculations for radiopharmaceuticals. J Nucl Med.2008;49:853–60. [PubMed]
20. Pereira JM, Stabin MG, Lima FR, Guimaraes MI, Forrester JW. Image quantification for radiation dose calculations limitations and uncertainties. Health Phys. 2010;99:688–701. [PMC free article][PubMed]
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@ Abdul Saeed Shah
Yes this study is carried out elsewhere in a joint work.
Sorry but your method is quite unusual. Could you better describe the gamma counter ? For me "gamma counter" is a table device for tube counts. Maybe you mean uptake probe generally used for thyroid.
Apart from that, absorbed dose to an organ is proportional to the integral subtended by the time activity curve in that organ. So you cannot obtain absorbed dose with only one time point (3.5 h ), unless your aget stays permanently trapped in the organ, without biological clearance.
I agree with Dr. Chiesa; first of all you need a time-activity curve, with measurement performed according to a time-table in function of the kinetics (slow, fast,...). Then you have to take into account the tissue attenuation, that reduces the counts measured, and correct for it; usually the simplest way to do it is the conjugate views method that requires previously to calibrate your system.
Hi Rafique,
As mentioned above you do require the activity within each of the different organs at several points in time (i.e. you need to have data from several rabbits, each sacrificed at these times).
There is a very good book published by Dr. Michael Stabin: "Fundamentals of Nuclear Medicine Dosimetry" (Springer, 2008). It has several case studies included (i.e. fuly worked examples), and also discusses the issues involved in translating animal dosimetry to human. I most thoroughly recommend it.
There is also freely available MIRD Pamphlet 16 (published by the Society of Nuclear Medicine, available online), which discusses the experimental design for what you are attempting to do (please correct me if I am wrong).
Good luck,
Andrew.
Hi Muhammad Rafique
I agree with Dr. Chiessa and Dr. Chicco. Also, you need work with a phantom if you want to convert counts in to organ injected activity (doses) .
Please, please consult scientific articles recommended by the researchers above-listed.
Have a good end of 2014 and happy new year.
With best wishes
Osvaldo
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