Room: Exhibit Hall | Forum 4
Purpose: Reliable skin dosimetry methods are critical for verifying the dose delivered to areas of adverse skin reactions potentially caused by accelerated partial breast brachytherapy. The purpose of this work is to characterize the accuracy and robustness of using Al2O3:C optically stimulated luminescence nanodots (OSLD) to measure skin dose delivered with the SAVI applicator (Cianna Medical, Aliso Viejo CA).
Methods: Patients implanted with a SAVI applicator were consented (Institutional Review Board (IRB) Protocol 0001750) to have an OSLD placed on their skin for in vivo dose measurement. Preplans were generated to determine the CT coordinates of the maximum skin dose point. Lasers were used to align and mark the OSLD position onto the patient based on offsets for measurement. A nonlinear calibration for an Ir-192 source and Monte Carlo dose correction factors that were previously developed for use with the Contura (Hologic, Marlborough, MA) applicator were applied to account for the lack of backscatter in skin dose measurements. OSLD measurements were compared to dose point calculations from a homogeneous dose (TG-43) prediction by Brachyvision version 15.5 (Varian, Palo Alto, CA).
Results: In vivo OSLD measurements that were corrected for spectral differences and the lack of backscatter for skin surface measurements agreed well with Brachyvision preliminary dose point calculations to within less than 6%. A 7% to 12% Monte Carlo correction (developed for use with the Contura breast applicator) was also applicable for the SAVI applicator. Air gaps and tissue invagination heterogeneities did not adversely impact the agreement between measured and calculated skin doses.
Conclusion: Clinical implementation of nanodots can be successfully used to measure maximum skin doses in patients treated with the SAVI applicator for accelerated partial breast brachytherapy. The dose accuracy for irradiation with an Ir-192 HDR source is comparable to measurements for photon and electron external radiation therapy.