Dose Assessment on the Mean Absorbed Estimates Derived from the Simple Approach Method Applying Marinelli-Quimby’s Formula for Ambient Risk Organs to Thyroid Uptake in the Administered ¹³¹I Radiopharmaceutical of Graves’ Disease Using PHITS and ICRP Reference Computational Voxel Phantom

Abstract

This study aimed to report a simple approach dosimetric tool for ambient risk organs/tissues (targets) to thyroid uptake (source) for ¹³¹I radiopharmaceutical of Gravesʼ disease. The dosimetric tool introduced in this study is based on the mean absorbed dose estimates and calculations by the Monte-Carlo code in radiation transport of particle heavy ion transport code system (PHITS), which is incorporated with Marinelli-Quimbyʼs formula in clinical use on therapeutic nuclear medicine using the International Com-mission on Radiological Protection (ICRP) reference adult male computational voxel phantom. More-over this feature can perform those dose estimates without fully calculating specific absorbed fractions (SAFs) or S-values relative to the radiation transport and energy deposition from source within targets, in-stead using the main absorbed dose (334.5500 Gy) of thyroid uptake determined by Marinelli-Quimbyʼs formula and precomputed dose ratio tables derived from PHITS between the thyroid uptake and ambient risk targeted organs/tissues (spleen, liver, pancreas, and thymus) and also easily working on 2D and 3D display procedure for radiation transport and energy deposition distribution mappings on ParaView and ANGEL (the latter is installed in PHITS) applications. To investigate the validation of our proposed simple approach dosimetric tool, we have compared it with different methods (PHITS direct method, ICRP Pub.53, IDACDose2.1, and OpenDose) to the mean absorbed dose estimates in the thyroid gland and those ambient risk targeted organs/tissues. We have found that it is in generally good agreement with those dose estimate results obtained in our proposed simple approach and others, and also represents that the PHITS calculation coupled with the Marinelli-Quimbyʼs formula is quite reliable enough to with-stand an absorbed dose estimate tool for other uptake organs/tissues working on sources themselves. It would seem that the proposed dosimetric tool has allowed any attending physician and medical physicist to provide easy and simply absorbed dose estimates for every normal and risk ambient organs/tissues to thyroid uptake in the administrated ¹³¹I radiopharmaceutical in therapeutic nuclear medicine on Gravesʼ disease.