SU‐E‐T‐28: Commissioning of OSLDs as An In‐Vivo Dosimeter in INTRABEAM Radiotherapy for Early Stage Breast Cancer

Purpose: To commission OSLDs for estimating skin dose for patients undergoing INTRABEAM radiation therapy for early stage breast cancer. Methods: Intrabeam system, using low energy X‐rays of 20keV effective energy, 0.64mm of Al HVL, deliver 20Gy to the spherical applicator surface. Optically Stimulated Luminescence Dosimeters (OSLDs Landauer screened nanoDOTs) were used for this study. OSLDs were water proofed using 3M Tegaderm film and held by a custom made solid water holder. OSLDs were irradiated in water at distances from the applicator surface ranging from 5mm up to 40mm. Measurements were repeated three times for each depth. Depth dose data in water as provided by the manufacturer is applied for estimating the delivered dose to OSLDs. Irradiated OSLDs were analyzed using microStar reader after giving a minimum 10 minutes delay to allow suppression of ambient phosphorescence. Calibration curves (Dose vs Counts) were generated for each applicator/probe combination and validated by performing comparisons in plastic water using PTW MARKUS planeparallel Ionization chamber and virgin OSLDs. Results: Calibration curves were generated for spherical applicators with diameters ranging from 2.5cm to 5cm. OSLD calibration curves were validated by performing a set of measurements in plastic water using ionization chamber & OSLDs. The results were within ±6% as expected based on the OSDL sensitivity uncertainty and OSLD positioning uncertainty. The reproducibility of OSLD measurements were ±2% (1σ). Conclusion: OSLDs can be used for in vivo dosimetry for intrabeam therapy and can accurately measure skin dose for patients receiving INTRABEAM therapy. Immediate reading and the ease of use provide added advantages to use OSLDs as an in vivo dosimeter. This calibration method incorporates the energy spectrum change with depth and hence the change in OSLD sensitivity with energy.