WE-G-BRB-07: Application of RADPOS in Vivo Dosimetry for QA of High Dose Rate Brachytherapy

Medical Physics
Amanda J CherpakJoanna E Cygler

Abstract

The RADPOS in vivo dosimetry system combines an electromagnetic positioning sensor with MOSFET dosimetry, allowing for simultaneous online measurements of dose and spatial position. In this work, we assess the potential use of RADPOS for measurements of motion and dose during prostate HDR brachytherapy. The RADPOS was positioned in the centre of a thin plastic tube supported by two parallel acrylic plates submerged in water. The detector was calibrated by sending an Ir-192 source into an adjacent tube, to positions ranging from 8.0 to -8.0 cm along the vertical axis in increments of 0.5 cm. The dwell time at each position was 20 s and the change in threshold voltage of the RADPOS dosimeter was recorded for each position. The expected dose for each source position was calculated and compared to RADPOS measurements to obtain a detector calibration coefficient (cGy/mV). The procedure was then repeated sending the Ir-192 source into 5 other tubes, located 1 to 10 cm away from the RADPOS. Source positions, dwell times, and position of the RADPOS detector were the same as for the calibration. The dose for each source position was determined by RADPOS measurements and calibration coefficient and compared to the expected dose. An avera...Continue Reading

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