Underutilization of hypofractionated whole-breast irradiation (HF-WBI) in large-breasted women may be partially explained by concerns about dose heterogeneity. Although modern planning may mitigate this issue, validated dosimetric guidelines are lacking. Our clinical pathway mandates hypofractionation, guided by institutional dosimetric criteria for plan evaluation. We examined acute radiation dermatitis rates with HF-WBI in large-breasted patients when our guidelines are followed and evaluated factors predictive for dermatitis.

Patients with whole-breast clinical target volumes (WB-CTV) of ≥1000 cm treated with HF-WBI were reviewed. WB-CTV V105, V107, and V110 were assessed. Our guidelines recommend limiting V105 to <10% to 15% and V110 to 0%. The highest grade of acute dermatitis was recorded. Potential clinical and dosimetric predictors of dermatitis were analyzed using logistic regression.

From 2012 to 2017, 505 breasts in 502 patients were treated with HF-WBI. The median WB-CTV was 1261.3 cm (interquartile range [IQR], 1115.3-1510.0). Most plans (99%) delivered 42.56 Gy in 16 fractions. A cavity boost of 10 Gy in 4 fractions was delivered in 99% of plans. Electrons were used in 69% of boost plans. Three-dimensional field-in-field technique was used in 68% of plans and inverse-planned intensity modulated radiation therapy in 32%. The median WB-CTV V105 was 9.7% (IQR, 5.6%-13.3%); the median WB-CTV V107 was 0.8% (IQR, 0.0%-2.5%). The WB-CTV V110 was 0% in 97.4% of plans (median, 0.0%; IQR, 0.0%-0.0%). Grade 1, 2, and 3 dermatitis rates were 55.0%, 40.8%, and 3.4%, respectively. On multivariate analysis, age >64 years (P = .016; odds ratio [OR] 4.0; 95% confidence interval [CI], 1.3-12.3), WB-CTV >1500 cm (P = .006; OR, 4.3; 95% CI, 1.5-12.3), body mass index ≥34 (P = .044; OR, 3.9; 95% CI, 1.0-14.5), and WB-CTV V105 >10% (P = .011; OR, 5.3; 95% CI, 1.5-19.3) predicted for grade 3 dermatitis.

With our institutional dosimetric guidelines, grade 3 dermatitis rates with HF-WBI in large-breasted women was <5%. WB-CTV V105 should be optimized to <10% to keep grade 3 dermatitis rates <2%.