Heart and Lung Dose Metrics in Radiation Therapy Patients Treated for Synchronous Bilateral Breast Cancer (SBBC): A Decade in Review (2011-2018)

Abstract

Heart and Lung Dose Metrics in Radiation Therapy Patients Treated for Synchronous Bilateral Breast Cancer (SBBC): A Decade in Review (2011-2018) Synchronous bilateral breast cancer (SBBC) is a relatively rare clinical presentation of which there is very little data, in the literature, describing organs at risk (OAR) dose limits for heart and lungs caused from radiation treatment (RT). Given that these patients typically have large irradiated treatment volumes relative to their unilateral counterparts, a retrospective review of heart and lung dose metrics was undertaken. The primary aim was to assess median mean heart dose (MHD), median mean lung dose (MLD) and the median volume of lung receiving 20Gy (V20) and 5Gy (V5). Secondary aims included analyses of 3D-CRT technique-based factors such as free-breath (FB), breath-hold (BH) and treatment field volumes associated with higher medium MHD and medium MLD. 92 patients who underwent bilateral RT from 2011-2018 were included. All patients received 3D-CRT conventional (50Gy in 25 fractions) or hypofractionation (42.56Gy in 16 fractions). Treatment volumes were as follows: whole-breast/chest wall RT (2 field tangential beams) +/- local-regional RT (3-4 field beams, including supraclavicular nodes +/- axillary nodes). When treatment included the internal mammary chain (IMC) this was considered wide-tangent RT. Boost data was not collected in this report. Median MHD (Gy) and median MLD (Gy) were stratified by conventional and hypofractionation. Factors investigated for correlation with higher median MHD/MLD were treatment volume, fractionation, heart/lung volumes, baseline-separation, heart shielding, FB and BH techniques. Overall medium lung V20 & V5 were collected. Backward stepwise selection was conducted in the multivariable analysis. The overall median MHD/MLD for conventional RT n = 52 and hypofractionated RT n = 40 was 2.96Gy and 2.03Gy for heart respectively and 10.53Gy and 6.35Gy for lung respectively. The median MHD/MLD multivariable analysis found locoregional RT n = 49 and the use of wide-tangent RT n = 20 to be associated with significantly higher MHD (P<0001) and MLD (P<0001). No other factors such as lung/ heart volumes, heart shielding n = 45 and the use of FB n = 79 versus BH n = 11 were identified as significantly associated with MHD and MLD. The median V20 and V5 lung volumes for conventional RT was 20% & 39% respectively and for hypofractionated RT 12% and 23% respectively. SBBC patients in our study showed overall acceptable MHD/MLD as well as V20 & V5 lung metrics when compared to those patients seen in the literature with unilateral breast RT. Furthermore, differences in median MHD/MLH in FB versus BH did not approach statistical significance. This suggests that careful treatment consideration in terms of BH technique and/or use of heart/lung shielding strategies are being appropriately made to minimize OAR dose limits to this patient demographic.