The testis is a radiosensitive tissue. It contains a large number of lobules, which in turn are composed of convoluted seminiferous tubules. The epithelium inside each tubule consists of a complex mosaic of supporting cells and germ cells of different sizes and degrees of maturation. These cells are known to have diverse sensitivity to radiation, those with the highest sensitivity being the spermatogonia, which form part of the basal cell layer, and those with the lowest sensitivity being the mature sperm cells closest to the lumen of the tubule. For many years, the internal dosimetry community has discussed the need for improvements to bring about more detailed, cell-level testicular dosimetry. This paper presents a small-scale dosimetry model for calculation of S factors for several different source-target configurations within the testicular tissue. Methods: A model of the testis was designed in which the lobules were approximated by a cross-section of seminiferous tubules arranged in a hexagonal pattern, with interstitial tissue between them. The seminiferous tubules were divided into concentric layers representing spermatogenic development in the seminiferous epithelium. S factors were calculated for electrons, photons, a-particles, and for 18 F, 90 Y, 99m Tc, 111 In, 125 I, 131 I, 177 Lu, and 211 At using Monte Carlo simulations. Results: For electrons with low energies the range was small, compared with the diameter of the seminiferous tubules, resulting in high energy deposition close to the source, whereas for higher electron energies more uniform energy deposition was seen, as expected. The same trend was seen for low-energy photons, whose mean free paths are small, compared with the diameter of the seminiferous tubules, resulting in high energy deposition close to the source, whereas for higher photon energies the location of the activity in the testis is less important. Conclusion: The model presented in this paper is a simplification of the organized chaos that constitutes the structure of the actual testis. However, it provides a relevant, small-scale anatomic model to help us understand the significance of the heterogeneity of radioactivity in this important radiosensitive tissue.
A heterogeneous distribution of radionuclides emitting low-energy electrons in the testicles may result in a significant difference between an absorbed dose to the radiosensitive spermatogonia and the mean absorbed dose to the whole testis. This study focused on absorbed dose distribution in patients at a finer scale than normally available in clinical dosimetry, which was accomplished by combining a small-scale dosimetry model with patient pharmacokinetic data. The activity in the testes was measured and blood sampling was performed for patients that underwent pre-therapy imaging with 111 In-Zevalin ® . Using compartment modeling, testicular activity was separated into two components: vascular and extravascular. The uncertainty of absorbed dose due to geometry variations between testicles was explored by an assumed activity micro-distribution and by varying the radius of the interstitial tubule. Results showed that the absorbed dose to germ cells might be strongly dependent on the location of the radioactive source, and may exceed the absorbed dose to the whole testis by as much as a factor of two. Small-scale dosimetry combined with compartmental analysis of clinical data proved useful for gauging tissue dosimetry and interpreting how intrinsic geometric variation influences the absorbed dose.
In this study, a model "ADM606M Portable Multifunction Ratemeter /Scalar" (Gamma GP110 Detector) was used to estimate the effective dose rate in (µSv.h -1 ). The data were analyzed for three specified hours per day (9:00 a.m., 11:00 a.m., and 1:00 p.m.) from January 2009 to June 2016. In July 2019, the gamma scout radiation meter (dosimeter) was used to measure the outdoor gamma effective dose rate (µSv.h -1 ) for the same building every minute for three hours, from 10 a.m. to 1 p.m., at 1m above the second floor of the building. The average effective dose rate and average Annual Effective Dose Rate were 0.158±0.013 µSv.h -1 and 0.2614145 mSv.y -1 , respectively, within acceptable limits. The excess lifetime cancer risk (ELCR) value was also assessed to be (0.91495×10 -³), which was found to be greater than the UNSCEAR, 2000 stated world average (0.29×10 -³). The risks of cancer morbidity and mortality for specific organs and tissues from external sources of low linear energy transfer (LET) radiation were also assessed. They showed biological effects associated with the potential long-term exposure of Dohuk city residents to natural background radiation.
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