SU‐F‐T‐654: Pacemaker Dose Estimate Using Optically Stimulated Luminescent Dosimeter for Left Breast Intraoperative Radiation Therapy

Abstract

Purpose:To assess and report the in vivo dose for a patient with a pacemaker being treated in left breast intraoperative radiation therapy (IORT). The ZEISS Intrabeam 50 kVp X‐ray beam with a spherical applicator was used.Methods:The optically stimulated luminescent dosimeters (OSLDs) (Landauer nanoDots) were employed and calibrated under the conditions of the Intrabeam 50 kVp X‐rays. The nanoDots were placed on the patient at approximately 15 cm away from the lumpectomy cavity both under and above a shield of lead equivalence 0.25 mm (RayShield X‐Drape D‐110) covering the pacemaker area during IORT with a 5 cm spherical applicator.Results:The skin surface dose near the pacemaker during the IORT with a prescription of 20 Gy was measured as 4.0±0.8 cGy. The dose behind the shield was 0.06±0.01 Gy, demonstrating more than 98% dose reduction. The in vivo skin surface doses during a typical breast IORT at a 4.5 cm spherical applicator surface were further measured at 5, 10, 15, and 20 cm away to be 159±11 cGy, 15±1 cGy, 6.6±0.5 cGy, and 1.8±0.1 cGy, respectively. A power law fit to the dose versus the distance z from the applicator surface yields the dose fall off at the skin surface following z^‐2.5, which can be used to estimate skin doses in future cases. The comparison to an extrapolation of depth dose in water reveals an underestimate of far field dose using the manufactory provided data.Conclusion:The study suggests the appropriateness of OSLD as an in vivo skin dosimeter in IORT using the Intrabeam system in a wide dose range. The pacemaker dose measured during the left breast IORT was within a safe limit.