SU‐GG‐T‐361: Feasibility of Making In‐Vivo Peripheral Dose Measurements Using a Portable Dosimeter System ‐ Beta Testing of a Novel Device

Abstract

Purpose: Peripheral Dose (PD) to structures such as testes, thyroid, or contra‐lateral breast has important clinical implications regarding the health of a patient. The purpose of this study was to determine utility of a new Portable Dosimeter System for PD measurements to critical structures outside of radiation fields. Method and Materials: Measurements were made using a pair of Portable Dosimeters, Model TN‐RD‐90 (Best Medical Canada Ltd.) At the time of the study, the device was going through the FDA approval process and this study was part of beta testing in a community hospital environment. The dosimeters were calibrated at high sensitivity of 3 mV/cGy as opposed to standard sensitivity of about 1 mV/cGy. Reproducibility and linearity of dose response were tested from a low dose range of 1–50 cGy. Peripheral dose measurements were made using solid water phantoms (100cm SSD; 10cm × 10cm field) on a 6MV (Novalis) and a 6/18 MV linac (Clinac‐2100EX) and compared them to ion chamber values. Results: Calibration of dosimeters showed both to have 3mV/cGy response. These MOSFETs were able to read a dose of 50 cGy or less with over 95% accuracy. Their dose linearity was excellent; R‐sq value was near 1 for both. Accuracy of dose readout decreased with lower dose values. At 1 cGy, the error was about 10% when averaged over 2 dosimeters. At a dose level of 0.25 cGy, the dosimeters' reproducibility and accuracy suffered. However, even with a 50% uncertainty in measured dose, the absolute dose derived was still clinically useful. Conclusion: The new mosfet dosimeters were easy to use, linear in response and reproducible. They will be clinically useful for in‐vivo dosimetry.