Internal dosimetry estimates using voxelized reference phantoms for thyroid agents

Abstract

This work presents internal dosimetry estimates for diagnostic procedures performed for thyroid disorders by relevant radiopharmaceuticals. The organ doses for 131Iodine, 123Iodine and 99mTc incorporated into the body were calculated for the International Commission on Radiological Protection (ICRP) reference voxel phantoms using the Monte Carlo transport method. A comparison between different thyroid uptakes of iodine in the range of 0–55% was made, and the effect of various techniques for administration of 99mTc on organ doses was studied. To investigate the necessity of calculating organ dose from all source regions, the major source organ and its contribution to total dose were specified for each target organ. Moreover, we compared effective dose in ICRP voxel phantoms with that in stylized phantoms. In our method, we directly calculated the organ dose without using the S values or SAFs, as is commonly done. Hence, a distribution of the absorbed dose to entire tissues was obtained. The chord length distributions (CLDs) were also computed for the selected source–target pairs to make comparison across the genders. The results showed that the S values for radionuclides in the thyroid are not sufficient for calculating the organ doses, especially for 123I and 99mTc. The thyroid and its neighboring organs receive a greater dose as thyroid uptake increases. Our comparisons also revealed an underestimation of organ doses reported for the stylized phantoms compared with the values based on the ICRP voxel phantoms in the uptake range of 5–55%, and an overestimation of absorbed dose by up to 2-fold for Iodine administration using blocking agent and for 99mTc incorporation.

Development of a 9-months pregnant hybrid phantom and its internal dosimetry for thyroid agents

“…This issue has been addressed earlier for the adult female ICRP voxel phantom [18]. Of particular importance is the fetal thyroid dose, which decreases by a factor of 15 as a result of increased maternal thyroid uptake.…”

Pulmonary embolism in pregnant patients: Assessing organ dose to pregnant phantom and its fetus during lung imaging

“…The detailed discussion on the contributions to internal doses could be found in Refs. [17,18,37]. However, the higher dose to fetal skeleton is yet clear.…”

“…used the stylized pregnant phantoms in dose estimation with three layers of 1.5 cm thickness mimic various body mass indexes . Several studies have been conducted to show the systematic discrepancy between data obtained with stylized phantom and image‐based computational phantoms . ICRP recommendations also confirm that external and internal dosimetry calculations should be performed using image‐based computational phantoms replacing the use of various stylized models .…”

“…12 Several studies have been conducted to show the systematic discrepancy between data obtained with stylized phantom and image-based computational phantoms. [13][14][15][16][17][18] ICRP recommendations also confirm that external and internal dosimetry calculations should be performed using image-based computational phantoms replacing the use of various stylized models. 19 With this context in mind, the question arises as to whether V/Q SPECT always outweighs CTPA in terms of dose to fetal or radiosensitive maternal organs.…”

The contributions of source regions to organ doses from incorporated radioactive iodine

“…In the previous paper, absorbed doses from 131 I and 123 I sodium iodide in voxel phantoms were calculated and compared with the values obtained for the corresponding stylized phantoms (Hoseinian-Azghadi et al, 2013). In this study, further details about the contributions of photons and electrons to organ doses from each source region are assessed and discussed for 131 I and 123 I.…”