
ORIGINAL ARTICLE 



Year : 2010  Volume
: 25
 Issue : 1  Page : 1011 


Physical dosimetry and mathematical dose calculation in nuclear medicine: A comparative study
Ali Shabestani Monfared^{1}, Mehrangiz Amiri^{2}
^{1} Department of Medical Physics, Babol University of Medical Sciences, Babol, Iran ^{2} Department of Nuclear Medicine, Shahid Beheshti Hospital, Babol University of Medical Sciences, Babol, Iran
Date of Web Publication  22May2010 
Correspondence Address: Ali Shabestani Monfared Babol University of Medical Sciences, Babol Iran
Source of Support: None, Conflict of Interest: None  Check 
DOI: 10.4103/09723919.63592
Abstract   
Objectives : This paper addresses a comparison between physical dosimetry and mathematical dose calculation in nuclear medicine. Materials and Methods: Dose rate was calculated by mathematical external dose calculation formula and by physical dosimetry from the surface of 38 adult patients' body referred to nuclear medicine department. Results of the methods were compared and correlation and regression tests were also performed. Results: Although the physical dosimetry data in this study are in good consistency with other researches, they are much lower than the results of mathematical dose calculation formula. The correlation coefficient between measured dose rate with calculated values derived by mathematical formula was found to be 0.852 (P value=0.148). Conclusion: It seems that physical dosimetry data are more accurate than the results of mathematical dose calculation. In case of using mathematical dose calculation formula, other correction factors should be considered and applied for getting reliable data. Keywords: Physical dosimetry, mathematical dose formula, nuclear medicine
How to cite this article: Monfared AS, Amiri M. Physical dosimetry and mathematical dose calculation in nuclear medicine: A comparative study. Indian J Nucl Med 2010;25:101 
How to cite this URL: Monfared AS, Amiri M. Physical dosimetry and mathematical dose calculation in nuclear medicine: A comparative study. Indian J Nucl Med [serial online] 2010 [cited 2020 Jan 19];25:101. Available from: http://www.ijnm.in/text.asp?2010/25/1/10/63592 
Introduction   
Evaluation of radiation effects on health in diagnostic imaging using radiopharmaceuticals needs the determination of radiation doses received by patients, technologists and environment. In nuclear medicine, patients underwent diagnostic imaging after radiopharmaceutical administration may give radiation dose to other patients, staff and members of public, which are in proximity to the patient. Potential radiation doses due to nuclear medicine procedures have been widely studied^{ [1],[2],[3],[4]} . However, the mathematical calculation in nuclear medicine still need to be adopted.
The aim of the present study is to compare the results obtained for dose calculation by using the mathematical formula and physical measurement.
Materials and Methods   
Thirtyeight adult patients (17 Bone, 14 Cardiac, 2 Renal, and 5 Thyroid scan) who were consecutively referred to the Nuclear Medicine Department of Shahid Beheshti Hospital (Babol University of Medical Sciences, Babol, Iran) were included in the study. The chief complaint / disease of the patients and the reports of the corresponding scans were also recorded. The net injected activity was recorded for each patient by measuring the remaining activities in the syringes. The dose rate was calculated by the mathematical external dose calculation formula^{ [6]} as shown a little later in the text and also by the calibrated dose rate meter (Graetz X5c Plus Germany), one meter from the surface of the patient's body at the diaphragmatic level, such as patient's mid torso, just before the scan.
Each dosimetric measurement was repeated thrice and the mean and standard deviation of the measured data were calculated and considered for further analysis. The correlation between the mathematically calculated and experimentally measured values was also derived by using the Pearson's correlation test.
Results   
The mean age and weight of the patients were 45.8 ± 16.0 years and 70.8 ± 14.2 Kg, respectively. Ten patients (26.3%) were male and 28 were female. The global mean net administered activity was found to be 19.5 ± 6.1 mCi. [Table 1] summarizes the results of the calculated and measured dose rate at 1 m distance from the patient's body, for the corresponding scans [Figure 1].
Discussion   
Results show that although the physical dosimetry data in this study are quite consistent with other researches,^{ [7],[8],[9]} they are much lower than the results of the mathematical dose calculation formula. The differences might be due to the source / measurement point geometry, radiopharmaceutical biological washout, and other physical factors that affect the results in practice (actual measurement). Meo et al have reported a good correlation between the experimental measurements and the Monte Carlo simulation for assessing the radiation dose from patients administered 90Ylabeled radiopharmaceuticals.^{ [10]} It may be due to the ability of Monte Carlo, as a strong and precise method, versus the simple mathematical dose calculation formula, which considers the patient as a static point source of radioactive material. Hippelδinen et al have indicated that physical dosimetry for personnel and dose calculations, according to AAPM TG108 guidelines, provide similar results.^{ [11]} A report by Siegel et al shows a major difference between point source versus line source model of dosimetry for patients undergoing nuclear medicine experiments.^{ [12]} However, they mentioned that in some cases of shielding, calculations should be carried out carefully to prevent the underestimation of shielding requirements. It seems that physical dosimetry data are more accurate than the results of the mathematical dose calculation. In case of using the mathematical dose calculation formula, other correction factors should be considered and applied for getting reliable data.
References   
1.  Guillet B, Quentin P, Waultier S, Bourrelly M, Pisano P, Mundler O. Technologist radiation exposure in routine clinical practice with 18FFDG PET. J Nucl Med Technol 2005;33:1759. 
2.  Chiesa C, de Sanctis V, Crippa F, Schiavini M, Fraigola CE, Bogni A, et al. Radiation dose to technicians per nuclear medicine procedure: Comparison between technetium99m, gallium67, and iodine131 radiotracers and fluorine18 fluorodeoxyglucose. Eur J Nucl Med 1997;24:13809. 
3.  Sichirollo AE, Bombardieri E, Cortona G, Marchesini R. External exposure of hot cell operators in nuclear medicine. Radiol Med 1998;96:6127. 
4.  Sudbrock F, Boldt F, Kobe C, Eschner W, Schicha H. Radiation exposure in the environment of patients after application of radiopharmaceuticals: Part 1: Diagnostic procedures. Nuklearmedizin 2008;47:26774. 
5.  Willegaignon J, Guimarγes MI, Stabin MG, Sapienza MT, Malvestiti LF, Marone MM, et al. Correction factors for more accurate estimates of exposure rates near radioactive patients: Experimental, point, and line source models. Health Phys 2007;93:67888. 
6.  Cember H. Introduction to Health Physics. Pergamon Press; 1983. p. 1956. 
7.  Dolezal J. Radiation exposure of the staff at the therapeutic and diagnostic nuclear medicine department: A single centre six years' retrospective study. Nuklearmedizin 2008;47:1757. 
8.  Cabral G, Amaral A, Campos L, Guimaraes MI. Investigation of maximum doses absorbed by people accompanying patients in nuclear medicine departments. Radiat Prot Dosimetry 2002;101:4358. 
9.  Amaral A, Cabral G, Campos L, Guimaraes MI. Exposure of persons accompanying patients in nuclear medicine departments. Cell Mol Biol 2002;48:5059. 
10.  Meo SL, Cicoria G, Montini G, Bergamini C, Campanella F, Pancaldi D, et al. Radiation emission dose from patients administered 90Ylabelled radiopharmaceuticals: Comparison of experimental measurements versus Monte Carlo simulation. Nucl Med Commun 2008;29:11005. 
11.  Hippelδinen E, Nikkinen P, Ihalainen T, UusiSimola J, Savolainen S. Personal radiation doses in PET/CT facility: Measurements vs. calculations. Radiat Prot Dosimetry 2008;132:5763. 
12.  Siegel JA, Marcus CS, Sparks RB. Calculating the absorbed dose from radioactive patients: The linesource versus pointsource model. J Nucl Med 2002;43:12414. 
[Figure 1]
[Table 1]
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