Hypofractionated Whole Breast Irradiation in Large-Breasted Women – Is There A Predictor for Acute Skin Toxicity?

Abstract

Underutilization of hypofractionated whole breast irradiation (HF-WBI) in large-breasted women may be partially explained by concerns over difficulty achieving dose homogeneity. Modern 3D and IMRT planning may help mitigate this issue, although validated dosimetric guidelines are lacking. Our clinical pathway mandates hypofractionation, and we have developed institutional guidelines for dosimetric criteria for our integrated cancer center network of 20 sites. We aimed to determine the rate of acute grade 3 dermatitis with HF-WBI in large-breasted patients when our institutional dosimetric guidelines are followed and evaluated factors potentially predictive for skin toxicity. A retrospective review was conducted of patients with whole breast clinical target volumes (CTV) of at least 1000 cc treated with HF-WBI between 2012 and 2017 within our network. Whole breast CTV (WB-CTV) V105, V107, and V110 were assessed. Institutional criteria recommend V105 <10-15% and V110 <0%. The highest grade of acute dermatitis based on CTCAE v4.0 was recorded. Potential clinical and dosimetric predictors of dermatitis were analyzed using logistic regression. During the study period, 506 breasts in 503 patients were treated with HF-WBI. Median WB-CTV volume was 1261.5 cc (IQR 1115.5-1509.1). Most plans (99%) delivered 42.56 Gy in 16 fractions. A tumor bed boost of 10 Gy in 2.5 Gy fractions was delivered in 99% of plans, and electrons were used in 67% of boost plans. 3D field-in-field technique was used in 68% of plans, while inverse-planning tangential beam IMRT was used in the remaining 32%. IMRT was more likely to be used with WB-CTV >1500 cc (p=0.022). Median WB-CTV V105 was 9.6% (IQR 5.6-13.3%), and median WB-CTV V107 was 0.8% (IQR 0.0-2.5%). WB-CTV V110 was 0% in 97.4% of plans (median 0.0%, IQR 0.0-0.0%). Rates of grade 1, 2, and 3 dermatitis were 55.1%, 41.0%, and 3.4%, respectively. Predictors for grade 3 dermatitis on univariate analysis included age >64, WB-CTV (cc), WB-CTV V105 (cc), and WB-CTV V105 >10% and V105 >15%, with a trend for WB-CTV V107 >2cc (p=0.065). On multivariate analysis, age >64 (p=0.020, OR 3.7, 95% CI 1.2-10.9), WB-CTV >1500 cc (p=0.002, OR 5.1, 95% CI 1.8-14.0), and WB-CTV V105 >10% (p=0.005, OR 6.4, 95% CI 1.8-22.9) predicted for grade 3 dermatitis. Rates of grade 3 dermatitis in patients with 0, 1, 2, and 3 of these factors were 1.0%, 1.2%, 4.2%, and 29.2%, respectively. With adherence to our institutional dosimetric guidelines, HF-WBI in large-breasted women is associated with a grade 3 dermatitis rate of <5%. To further reduce risk of skin toxicity in this population, WB-CTV V105 should be optimized at <10% in order to keep grade 3 dermatitis rates <2%.Abstract 1150; TableVariableNRate of Grade 3 DermatitisAge ≤64272 (54%)1.8% >64234 (46%)5.1%WB-CTV ≤1500 cc376 (74%)1.9% >1500 cc130 (26%)7.7%WB-CTV V105 ≤10%271 (54%)1.1% >10%235 (46%)6.0% Open table in a new tab