SU-GG-T-44: Evaluation of Xoft Electronic Brachytherapy System for Intraoperative Treatments

Abstract

Purpose: The main objective was to evaluate and commission the Xoft Electronic Brachytherapy System for intraoperative treatments. Method and Materials: Using the manufacturer supplied phantom, we evaluated and commissioned the Xoft Electronic Brachytherapy system. We tested well‐chamber constancy and intercomparison, beam output stability with time, start/end effects, and performed radiation surveys. Other checks recommended by the AAPM TG152 were evaluated. Results The Ir‐192 calibrated well chamber is 3.7 times more sensitive when irradiated with the Xoft source than the Xoft calibrated well chamber. Expectation was that both chambers would give approximately the same reading because the Xoft integrated well chamber is cross calibrated in I‐125 source. It takes about 28s for the doserate from the Xoft Unit to ramp up to the treatment doserate. The unit delivers 9s worth of treatment during the ramp up phase. For treatment times less than 100s, this would introduce a dosimetry error of about 10% which will be repeated if there is a treatment interruption. Xoft Unit output may vary by up to 5% between 0.25 and 30 minutes. This variation is source dependent. So the minimum time used to collect charges for the AAPM‐TG61 calibration should be 1 minute, not 0.25 minute. Radiation surveys during treatment indicate that surface and intraoperative treatments give rise to exposure rates of 200mR/hr, 30cm from treatment area. Conclusions: Well chamber calibration inconsistency for Xoft Unit needs further investigation. Ramp up time accounts for 9s equivalent treatment time. Correction needed for treatment time less than 150 seconds. Charges for TG61 calibration should be collected for at least 1 minute, not 0.25 minute. Intraoperative and surface treatment produces exposure rate of 200mR/hr at distances of 30 cm. Exercise extreme caution by standing behind lead shield or wearing a lead apron.

Characteristics of miniature electronic brachytherapy x‐ray sources based on TG‐43U1 formalism using Monte Carlo simulation techniques

“…This is approximately three times that of a 10 Ci HDR 192 Ir source. 9 The XAEBS was approved by the FDA to be used in intracavitary accelerated partial breast irradiation, 10 endometrial treatments, 11 intra-operative radiation therapy, 12 and skin cancer treatment using surface applicators. 13 Photon spectra, 9,14 depth dose modulation, 15 tissue heterogeneities, [16][17][18][19] relative biological effectiveness, 17 and intensity modulated electronic brachytherapy 20 for XAEBS are not well-understood and require further investigation.…”