Lung and cardiac tissue doses in left breast cancer patients treated with single-source breast brachytherapy compared to external beam tangent fields

Purpose We performed a retrospective analysis of doses to normal critical structures in 26 women with left-sided breast tumors treated with a high-dose-rate single source brachytherapy (SSB) system, versus whole breast external beam tangent fields (EBTF) using a computer model. Methods and materials Each patientʹs EBTF radiation plan consisted of ipsilateral tangent fields normalized to 46 Gy. A complementary SSB radiation plan was designed to deliver 34 Gy in 10 fractions at 1 cm into tissue enclosing a sphere of diameter 4.6 cm at tumor bed, simulating our institutionʹs experience with the MammoSite™ applicator. Critical structure volumes and doses analyzed included the volume of whole heart and left ventricle receiving >25 Gy, and left lung (LL) receiving 20 and 13 Gy for EBTF plans. For SSB we determined the linear quadratic 2-Gy-equivalent high-dose-rate doses of 23.4, 20, and 14 Gy to be equivalent to 25, 20, and 13 Gy, respectively. We then compared the two doses for each critical structure. Results The percent of whole heart receiving >25 Gy equivalent using EBTF and SSB was 2% and 0% (mean dose 2.52 vs. 1.65 Gy), left ventricle receiving >25 Gy using EBTF and SSB was 3% and 0% (mean dose 3.78 vs. 2.68 Gy), LL receiving >20 Gy using EBTF and SSB was 11.5% and 0.5%, and LL receiving >13 Gy using EBTF and SSB was 12.6% and 1.85% (mean dose to LL was 6.06 Gy for EBTF vs. 2.25 Gy for SSB), respectively. Conclusions When compared to EBTF, breast brachytherapy with SSB is associated with a significant decrease in mean dose and percentage volume receiving a given dose for each organ.