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Characterization and Validation of Optically Stimulated Luminescent Dosimeters for In-Vivo Surface Dosimetry of HDR Breast Brachytherapy Treatments

J Van Schelt

J Van Schelt1*, L Young1, L Wootton1 , J Meyer1 , C Dempsey1, 2, 3 , (1) University Washington Department of Radiation Oncology, Seattle, WA, (2) The University of Newcastle School of Health Sciences, Newcastle, NSW, Australia, (3) Calvary Mater Newcastle Hospital, Newcastle, NSW, Australia.


SA-B-BRA|B-9 (Saturday, March 18, 2017) 10:30 AM - 12:30 PM Room: Ballroom A|B

Purpose: Optically stimulated luminescent dosimeters (OSLDs) are routinely used as surface in-vivo dosimeters in external beam radiation therapy, however there have been few studies investigating their use in high dose rate (HDR) brachytherapy. The TG-43 dose calculation algorithm does not account for the lack of backscatter at the skin surface so it is difficult to accurately determine the actual dose received. The purpose of this work is to evaluate the use of OSLDs for in-vivo measurements of skin dose as a method for catching setup and planning errors in breast brachytherapy patients.

Methods: Commercial OSL dosimeters (Landauer nanoDot) and EBT3 film were characterized in-phantom under full scatter conditions for energy and dose response to Ir-192 radiation up to 5 Gy, with the film serving as a second check. Clinically relevant surface measurements were completed on a phantom with OSLDs and film to quantify the TG-43 dose over-estimation at the skin surface for source depths ranging from 1.5 to 7 cm. Monte Carlo simulations were performed with EGSnrc to verify the trends and determine any corrections necessary to convert OSLD measurements into a skin dose value.

Results: The OSLDs measure systematically lower doses at the surface than TG-43 calculates, with greater differences as the depth of the source increases: from 2% at 1.5 cm to 9% at 7 cm. The film measurements showed greater scatter but did agree with the OSLDs. The Monte Carlo simulations confirmed the OSLD trend and show that the dose to the surface will be less than that in a homogenous phantom by 7% to 12%. The information needed to convert clinical measurements to skin dose was generated.

Conclusion: A procedure for using OSLDs to measure skin dose for patients receiving Ir-192 HDR brachytherapy was developed and validated. Clinical implementation as a standard procedure is ongoing.

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