SU-E-T-334: APBI Contralateral Breast Dose

Abstract

Purpose: To determine the dose to the contralateral breast during Accelerated Partial Breast Irradiation (APBI) treatment, simulation and daily QA, and to compare it to external beam published values. Methods: TLD‐100 packets were used to measure the dose to the most medial aspect of the contralateral breast during APBI simulation, daily QA, and treatment. Patient measurements were used as opposed to phantom data so as to measure more clinically relevant data that includes variability in patient size and geometry. All patients in this study were treated with a SAVI interstitial applicator for ten fractions to a total dose of 3.4Gy. Measurements were made for two or three fractions of the treatment course using three packets of TLD‐100 for each measurement. A mark was placed on the patient's skin on the medial aspect of the opposite breast. Three TLD packets were taped to this mark during the pre‐treatment simulation. Simulations and QA were conducted in our CT suite and consisted of an AP and Lateral scout or a mini scan if rotation was a concern. After the simulation the TLD packets were removed and the patients was moved to the HDR vault where three new TLD packets were taped onto the patient at the skin mark. Treatment was administered with a Nucletron HDR afterloader using Iridium 192 as the treatment source. Post treatment, the TLD were read (along with the simulation and QA TLD and a set of standards exposed to a known dose of 6 MV photons). Results: Measurements indicate a worst case exposure to the contrlateral breast of less than 250cGy. As would be expected, inner quadrant implants Result in higher dose than outer quadrants. Conclusion: Compared to external beam breast tangents, these results point to less dose to the contralateral breast when using APBI.