Assessment of Applicability of Portable HPGe Detector with In Situ Object Counting System based on Performance Evaluation of Thyroid Radiobioassays

Abstract

Background: Different cases exist in the measurement of thyroid radiobioassays owing to the individual characteristics of the subjects, especially the potential variation in the counting efficiency. An In situ Object Counting System (ISOCS) was developed to perform an efficiency calibration based on the Monte Carlo calculation, as an alternative to conventional calibration methods. The purpose of this study is to evaluate the applicability of ISOCS to thyroid radiobioassays by comparison with a conventional thyroid monitoring system. Materials and Methods: The efficiency calibration of a portable high-purity germanium (HPGe) detector was performed using ISOCS software. In contrast, the conventional efficiency calibration, which needed a radioactive material, was applied to a scintillator-based thyroid monitor. Four radioiodine samples that contained $^{125}I$ and $^{131}I$ in both aqueous solution and gel forms were measured to evaluate radioactivity in the thyroid. ANSI/HPS N13.30 performance criteria, which included the relative bias, relative precision, and root-mean-squared error, were applied to evaluate the performance of the measurement system. Results and Discussion: The portable HPGe detector could measure both radioiodines with ISOCS but the thyroid monitor could not measure $^{125}I$ because of the limited energy resolution of the NaI(Tl) scintillator. The $^{131}I$ results from both detectors agreed to within 5% with the certified results. Moreover, the $^{125}I$ results from the portable HPGe detector agreed to within 10% with the certified results. All measurement results complied with the ANSI/HPS N13.30 performance criteria. Conclusion: The results of the intercomparison program indicated the feasibility of applying ISOCS software to direct thyroid radiobioassays. The portable HPGe detector with ISOCS software can provide the convenience of efficiency calibration and higher energy resolution for identifying photopeaks, compared with a conventional thyroid monitor with a NaI(Tl) scintillator. The application of ISOCS software in a radiation emergency can improve the response in terms of internal contamination monitoring.

Keywords

• Radiation emergency;
• Radioactivity;
• Radioiodine;
• Monte Carlo method;
• Radiobioassay

File

Download PDF

Acknowledgement

Supported by : Korea Institute of Radiological and Medical Sciences (KIRAMS)

References

1. Dantas BM, Lucena EA, Dantas ALA, Santos MMS, Juliao LQC, Melo DR, Sousa WO, Fernandes PC, Mesquita SA. A mobile bioassay laboratory for the assessment of internal doses based on in vivo and in vitro measurement. Health Phys. 2010;99:449-452. https://doi.org/10.1097/HP.0b013e3181c03e41
2. Yoo JR, Park SY, Yoon SY, Ha WH, Lee SS, Kim KP. Radiobioassay performance evaluation of urine and faeces samples for radiation emergency preparedness. J. Nucl. Sci. Technol. 2016;53(11):1742-1748. https://doi.org/10.1080/00223131.2016.1153437
3. International Commission on Radiological Protection. Dose coefficients for intakes of radionuclides by workers. ICRP publication 68. 1994;1-17.
4. International Commission on Radiological Protection. Individual monitoring for internal exposure of workers. ICRP publication 78. 1997;3-18.
5. National Council on Radiation Protection and Measurements. Use of bioassay procedures for assessment of internal radionuclide deposition. NCRP report no. 87. 1987;19-31.
6. International Atomic Energy Agency. Indirect methods for assessing intake of radionuclides causing occupational exposure. Safety reports series no. 18. 2000;15-21.
7. Canada Nuclear Safety Commission. Thyroid screening for radioiodine. Regulatory document no. 58. 2008;1-15.
8. United Nations Scientific Committee on the Effects of Atomic Radiation. Sources, Effects, and Risks of Ionization Radiation. UNSCEAR 2000 report. 2000;338-342.
9. Bento J, Martins B, Teles P, Neves M, Colarinha P, Alves F, Teixeira N, Vaz P, Zankl M. Performance assessment and uncertainty evaluation of a portable NaI-based detection system used for thyroid monitoring Radiat. Prot. Dosim. 2012;151:252-261. https://doi.org/10.1093/rpd/ncs011
10. Fantinova K, Fojtik P. Monte Carlo simulation of the BEGe detector response function for in vivo measurements of 241Am in the skull. Radiat. Phys. Chem. 2014;104:345-350. https://doi.org/10.1016/j.radphyschem.2014.01.005
11. National Council on Radiation Protection and Measurements. Management of persons accidentally contaminated with radionuclides. NCRP report no. 65. 1979;20-44.
12. International Commission on Radiation Units and Measurements. Phantoms and computational models in therapy, diagnosis and protection. ICRU report no. 48. 1992;31, 98.
13. Ghare VP, Patni HK, Akar DK, Rao DD. Counting efficiency of whole-body monitoring system using BOMAB and ANSI/IAEA thyroid phantom due to internal contamination of I-131. Radiat. Prot. Dosim. 2014;162:230-235. https://doi.org/10.1093/rpd/nct269
14. International Atomic Energy Agency. Quantifying uncertainty in nuclear analytical measurements. IAEA-TECDOC-1401. 2004;103-126.
15. Health Physics Society. Performance criteria for radiobioassay. ANSI/HPS N.13.30-1996. American National Standards Institute. 1996;23-29.
16. Health Physics Society. Performance criteria for radiobioassay. ANSI/HPS N.13.30-2011. American National Standards Institute. 2011;6-12.
17. International Organization for Standardization. Radiation protection - performance criteria for radiobioassay: ISO 28218. 2010;7-12.
18. Morris KE, Mueller WF, Blanc P, Bronson F, Croft S, Field MB, Nakazawa DR, Venkataraman R, Zhu H. The efficiency characterization of Germanium detectors at energies less than 45 keV. Waste Management Conference. Phoenix, AZ. March 7-11, 2012.
19. Damet J, Bochud FO, Bailat C, Laedermann JP, Baechler S. Variability of radioiodine measurements in the thyroid. Radiat. Prot. Dosim. 2010;144:326-329.