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

Background: 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. Methods: 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*radius 2 . 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. Results: 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. Conclusion: 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.