Patient dosimetry for total body irradiation using single-use MOSFET detectors

Abstract

We have studied the usefulness of a new type of solid state detector, the OneDose single-use MOSFET dosimeter, for entrance dose measurements for total body irradiation (TBI). The factory calibration factors supplied by the manufacturer are applicable to conventional radiotherapy beam arrangements and therefore may not be expected to be valid for TBI dosimetry due to the large field sizes and extended source-to-axis distances used. OneDose detectors were placed under 1-cm thick bolus at the head, neck, and umbilicus of 9 patients undergoing TBI procedures.  Thermoluminescent dosimeters (TLDs) were placed beside the detectors. We found the OneDose readings to differ from the TLD readings by 4.6% at the head, 1.7% at the neck and 3.9% at the umbilicus, with corresponding standard deviations of 3.9%, 2.2%, and 2.7%. For all patient measurements, 95% of the OneDose readings fell within 3.3 ± 6.0% of the TLD readings.  Anthropomorphic phantom measurements showed differences of -0.1% at the neck, and -1.2% midway between the phantom’s carina and umbilicus. Our results suggest that these detectors could be used for TBI QA monitoring, although TLDs should remain the standard when critical dose measurements are performed.  If they are to be used for TBI, the use of more than one OneDose detector at each location is strongly recommended.  They could also be calibrated in phantom using the TBI geometry configurations used for patient treatment to obtain the institution-specific correction factors for better applicability for TBI dosimetry.