Rates and Predictors of Acute Toxicity after Accelerated Partial Breast Irradiation

Abstract

<h3>Purpose/Objective(s)</h3> 10-year data from the Florence trial demonstrated reduced acute and late toxicities with accelerated partial breast irradiation (APBI) compared to standard whole breast irradiation. However, given acceleration and higher dose per fraction, there may be subsets of patients at higher risk of toxicity. The objective of this study was to describe the acute toxicity rates at our institution and evaluate predictors of toxicity after 5 fraction APBI. <h3>Materials/Methods</h3> The charts of 286 patients who received APBI were identified from an institutional registry. Their records were reviewed to collect clinicopathologic features. Adverse events (CTCAE criteria) occurring within 3 months were classified as acute and after 3 months as subacute. Categorical variables were compared using Fisher's exact tests. Predictors of toxicity were evaluated using logistic regression. <h3>Results</h3> Median follow-up was 1.03 years. Mean age was 66.2 years. Racial composition was 88.9% white, 7.7% black, and 3.3% other. The prevalence of comorbidities were as follows: CAD (5 patients, 1.8%), COPD (4, 1.5%), obesity (109, 42.7%), asthma (18, 6.6%), HTN (113, 41.5%), diabetes (33, 12.1%), and dyslipidemia (101, 37.1%). The proportions of active, former, and never smokers were 6.3%, 36%, and 57.7%, respectively, while the proportions of active, former, and never alcohol drinkers were 88.2%, 1.7%, and 10.1%, respectively. All patients received 30 Gy in 5 fractions to the partial breast, with 209 (76.6%) patients receiving radiation QOD and 64 (23.4%) receiving daily. 56% of cancers were left sided, and 44% were right sided. 18 patients (6.6%) received chemotherapy, and 207 (76%) received hormone therapy. The majority of patients had T1 disease (215, 78.8%) while 46 (16.8%) had Tis and 12 had T2 disease (4.4%). Regarding acute toxicity, G1 dermatitis, G1 fatigue, and G2 fatigue occurred in 84 (30.8%), 36 (13.2%), and 1 (<1%) patient(s), respectively with no Grade 3 or greater toxicities. Predictors of any acute toxicity on univariate analysis included BMI (p<0.001), CAD (p=0.0064), never alcohol users (p=0.011), and radiation delivered QOD (p=0.0049), of which never alcohol users (p=0.02) and radiation delivered QOD (p=0.025) persisted on multivariate analysis. Subacute dermatitis and worsened cosmetic appearance occurred in 8 (3.1%) and 16 patients (10.2%), respectively. Lymphedema occurred in 1 patient, and telangiectasias were not present in any patients. Race other than black or white (p=0.03), CAD (p=0.013), and asthma (p=0.031) were predictors of subacute toxicity on univariate and multivariate analysis. <h3>Conclusion</h3> Overall acute and subacute adverse event rates after APBI were low, consistent with the Florence trial. Comorbidities, including CAD and asthma, and non-black non-white race may predict for higher risk of subacute toxicity. Longer follow-up is needed to evaluate if this translates to late-term toxicity.