Factors Affecting Mean Heart Dose in Patients Receiving Breast Radiotherapy from 2011 to 2018 in a Single Institution

Abstract

Introduction: Breast cancer radiotherapy (RT) can increase the risk of cardiac disease with increasing dose; as such, reducing excessive dosage to the heart is a concern for clinicians. The purpose of the present study was to assess mean heart dose (MHD) in patients with breast cancer receiving RT, where it was hypothesized that MHD decreased over time.

Methods: Patients planned for adjuvant unilateral whole breast/chest wall RT from 2011 to 2018 were included for a retrospective chart-review at a single-institution, academic center. MHD (Gy) was summarized by laterality, fractionation, and heart-sparing techniques.

Results: A total of 4,687 patients were included. The median MHD for left-sided conventional RT (50 Gy in 25 fractions) was 2.16 Gy across all years, decreasing until 2015 and increasing after. Median MHD for left-sided hypofractionated RT (42.6 Gy in 16 fractions) was 1.47 Gy, also decreasing until 2015 and increasing after. The increase in MHD after 2015 was attributed to a significant increase in the use of wide tangents (including internal mammary chain) after 2015 (P < .0001). Several treatment factors were associated with higher MHD in both right- and left-sided cancers, including locoregional RT, high tangents, wide tangents, bolus, heart shielding, treatment to the chest wall, higher volume of tissue irradiated by tangential fields, higher baseline breast separation values, and smaller heart volume. After adjusting for laterality and fractionation in the multivariate analysis, locoregional RT, wide tangents, heart shielding, boost, treatment to the chest wall, higher volume of tissue irradiated by tangential fields, higher baseline breast separation, and lower heart volume were significantly associated with higher MHD (P < .0001).

Discussion/conclusions: MHD should be considered when determining the most appropriate RT techniques for both right- and left-sided cancers as higher MHD was significantly associated with various treatment techniques and patient factors.

Keywords: Breast radiotherapy; conventional fractionation; heart-sparing; hypofractionation; mean heart dose.