Room: AAPM ePoster Library
Purpose: To determine the feasibility of performing catheter-by-catheter analysis of in-vivo rectal dosimetry measurements performed with MOSkin dosimeters, during trans-rectal ultrasound (TRUS) based high dose rate prostate brachytherapy (HDR pBT).
Methods: Four MOSkin dosimeters were coupled to a TRUS probe during 20 TRUS based HDR pBT treatment fractions. The HDR pBT treatments were delivered using the Oncentra Prostate brachytherapy treatment planning system (BTPS) (Elekta Brachytherapy, Veenendaal, Netherlands) with a prescription of 9 Gy. The measured MOSkin doses were retrospectively compared to the doses predicted by the BTPS for the total treatment fraction, as well as on a per catheter basis, by placing a point of interest in the BTPS at the known position of the MOSkin dosimeter in the reference frame of the BTPS.
Results: The total combined measurement uncertainty of the system was 11.5% (k=1). The average relative percentage difference between MOSkin measured and BTPS predicted doses for a total treatment fraction was -1.6% ± 11.1% (k=1), with a maximum of 25.7% and a minimum of -29.2%. Sixty-eight percent of the measured fractions fell within the ±11.5% uncertainty range, relative to the TPS predicted dose. The average relative percentage difference on a catheter-by-catheter basis was +2.5% ± 16.9% (k=1). Sixty-four percent of the measured catheters fell within the ±11.5% uncertainty range, relative to the TPS predicted dose.
Conclusion: Catheter-by-catheter analysis of MOSkin in-vivo rectal dosimetry during TRS based HDR pBT was found to be feasible. Catheter-by-catheter analysis of the data improved the error catching ability of the system by providing additional information about which catheter the error may have occurred. The use of multiple MOSkin dosimeters also provided additional information about the geometrical location of the potential error within the prostate.