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

Abstract 

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 patient's EBTF radiation plan consisted of ipsilateral tangent fields normalized to 46Gy. A complementary SSB radiation plan was designed to deliver 34Gy in 10 fractions at 1cm into tissue enclosing a sphere of diameter 4.6cm at tumor bed, simulating our institution's experience with the MammoSite™ applicator. Critical structure volumes and doses analyzed included the volume of whole heart and left ventricle receiving >25Gy, and left lung (LL) receiving 20 and 13Gy for EBTF plans. For SSB we determined the linear quadratic 2-Gy-equivalent high-dose-rate doses of 23.4, 20, and 14Gy to be equivalent to 25, 20, and 13Gy, respectively. We then compared the two doses for each critical structure.

Results

The percent of whole heart receiving >25Gy equivalent using EBTF and SSB was 2% and 0% (mean dose 2.52 vs. 1.65Gy), left ventricle receiving >25Gy using EBTF and SSB was 3% and 0% (mean dose 3.78 vs. 2.68Gy), LL receiving >20Gy using EBTF and SSB was 11.5% and 0.5%, and LL receiving >13Gy using EBTF and SSB was 12.6% and 1.85% (mean dose to LL was 6.06Gy for EBTF vs. 2.25Gy 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.

Keywords: Radiotherapy, MammoSite, Brachytherapy, Breast cancer, Lung complications, Heart complications