A Quantitative Evaluation of the Effects of Radiation Therapy on the Post-Surgical Breast.

Abstract

Radiation (RT) effects on breast volume may impact breast-conserving therapy (BCT) outcomes, but quantitative information is lacking regarding the extent/timing of volume loss. This study aimed to quantify volume loss by assessing changes in irradiated breasts. Breast volume changes were calculated for 113 patients (115 breasts) following T1 tumor lumpectomies. From preoperative baseline to seven years post-radiation, volumes were calculated from mammograms using π/3* height*radius2. Paired t-tests assessed change over time, with subset analyses of tumor/breast volumes of ≤ 10% (n=67) and > 10% (n=48). Multivariable regression assessed volume change as a function of age, smoking history, diabetes, radiation dosage, fractions, technique, treatment length, boost dose, chemotherapy (hormonal or cytotoxic), baseline breast volume, and time since treatment. Patients lost 8.3% of breast volume during surgery. One year following BCT/RT, volume loss was 19.3%. By year five, total volume loss was 26.6%.Subset analyses demonstrated that in addition to lumpectomy defects, five-year volume loss was 21.7% for tumor/ breast volume > 10% and 29.5 % for tumor/ breast volume ≤ 10%. Volume loss between subgroups was not significantly different (p=0.37). Larger breast volume was a significant predictor of greater volume loss for all five years (p<0.001), followed by diabetes and smoking history. Patients with T1 tumors undergoing BCT/RT may lose approximately 20% of breast volume (beyond specimens) within a year, with continued loss for five years. Volume change did not differ significantly according to baseline breast volume, although larger breasts may experience comparatively larger volume changes.