A Prospective Study for the Dose Calculation of the Thyroid and Salivary Glands for Prostate Cancer Patients

Abstract

Studies involving dose to the thyroid for medical treatments have not been documented in recent years despite the increase in treatment via nuclear medicine to treat various cancers. Most thyroid dose calculations have been done through the Medical Internal Radiation Dose (MIRD) method, a mathematical model representing the human anatomy and Monte-Carlo (MC) simulation for the medical treatment of patients. Little data exists for the thyroid dose from the I-131 treatment when the thyroid is not the target organ. As Prostate Specific Membrane Antigen (PSMA) trials and nuclear medicine procedures become more common, considerations need to be taken regarding patient safety. Images were acquired via a General Electric (G.E.) Discovery 670 Nuclear Medicine, this machine allowed for patient-specific time-activity curves. Three patients undergoing this clinical trial IRB 00000176, a multicenter, randomized, controlled phase-2 study were treated with I-131 for prostate cancer. Dose to the thyroid and salivary glands from the I-131 1095 PSMA treatment were calculated using the MIRD equation in pamphlet 21 [2] time-dependent mean absorbed dose. Based on individual time activity curves, biological half-lives were extracted and compared to I-131 saline bag. Patients were imaged within 24 hours and follow up images up to 170 hours after administration of I-131 1095 PSMA. Calculations showed the average dose to the thyroid was 9.92E-03 mGy, a value added towards providing individualized medicine for patient tracking and safety across all future nuclear medicine procedures for the patient.