GAMOS DICOM Simulation on Occupational EL Dose due to 99mTc and 131I Exposures in Nuclear Medicine Departments

Abstract

Radiation induced cataracts is a disease that is common amongst radiation exposed staff. About 30 percent of retired occupational radiation workers developed eye lens (EL) cataracts. Epidemiological studies on radiation therapy patients, occupational workers, and atomic bomb survivors show that 0.5 Gy of acute or fractioned radiation dose to EL causes one or both lens to cloud. The annual EL dose limit drawn by the International Commission for Radiation Protection (ICRP) was 150 mSv and was changed in 2012 to 20 mSv averaged over 5 years, with no single year exceeding 50 mSv. The limited number of researche done in Nuclear Medicine (NM) clinics with the Hp(3) dosimeters suggest that the annual EL dose from three procedures is measured to be between 4.5 and 9 mSv (i.e. dispensing, preparing and administering). These procedures are performed when the radioactive materials are in closed shielded containers or behind a barrier. Common radioactive material handled by occupational workers in NM clinics are 99mTc and 131I. They pose less radiation hazard to workers EL in the three procedures when they are behind shielded containers. Moreover, once the radioactive material is administered into patients, they become open sources and pose more radiation hazard to workers. The Hp(3) dosimeter is a new uncommon dosimeter. Many radiation facilities use the Hp(0.07) and Hp(10) dosimeters coupled with many conditions and conversion factors to find approximate results. Therefore, simulations are performed to find the EL dose. However, some simulations are performed with little flexibility in simulation geometry, others utilize low-quality phantoms or present the simulation results in terms of fluxes or energy ranges. In the present study, the NM worker EL dose is simulated by utilizing a high-resolution Digital Imagning Communication in Medicine (DICOM) image in GEANT4 Archeticture for Medical Oriented Simulation (GAMOS). A water cylinder homogenously filled by radioactive material, representing the administered patient, was created in the simulation. The worker exposure scenario was simulated by placing the cylinder in three different directions and five different distances with respect to the DICOM image. The results of the simulation reveal that the highest occupational EL radiation dose is received from the anterior-posterior direction, followed by the lateral, and the posterior-anterior directions. The results of the conservative simulated scenario reveal that the worker EL dose is exposed to three tenths of the annual dose limit after 110 131I patients, or 300 99mTc patients.