R.V. Hymas

Dosimetric predictors of toxicity and cosmesis in women treated with hypofractionated whole-breast irradiation.

77 Background: Large breast volume (BV) and distance of separation (DoS) have historically served as exclusionary criteria for hypofractionated whole breast irradiation (H-WBI). We investigate dosimetric parameters impacting toxicity and cosmesis. METHODS 299 consecutive patients with T0-2,N0-1,M0 breast cancer were treated with H-WBI at a single institution from 2007-2013. 4,256 cGy were delivered in 16 fractions via tangent photon beams utilizing inverse planning, with objectives to limit the V105 to 15%, the V110 to 2%, and the V115% to <0.1%. 227 patients with available treatment planning information and at least 6 months of follow-up (FU) were analyzed. Dosimetric parameters were correlated with acute (≤6 months post-treatment) and chronic toxicity and overall cosmesis. Proportions of toxicity grade and cosmesis score were compared with chi-square or Fisher exact tests. RESULTS With a median FU of 2.7 years (range 0.4-6.6 years), there were no local or regional recurrences, 1 distant failure, and one in-field angiosarcoma. Rates of any acute and chronic grade 1/2/3 toxicity were 47%/32%/9% and 53%/22%/7%. Cosmesis (beyond 6 months) was reported as excellent, good, and fair in 45%, 55%, and <1% of patients. The V105 was the best predictor for cosmesis and chronic toxicity, with a V105≤10% being associated with better cosmesis (excellent vs fair/poor) and lower toxicity (grade 0 vs grade 1 vs grade 2/3) compared to a V105>10% (p=0.09 and 0.03, respectively). The mean DoS was 22 cm, with 22% and 3% of patients having a DoS greater than 25 cm and 28 cm. The mean BV was 1523 cc, with 19% and 5% having a BV greater than 2000 cc and 2500 cc. Neither a larger DoS nor a larger BV correlated with an inability to achieve a V105≤10% (p= 0.37 and p=0.13, respectively). Neither DoS nor BV predicted for worse acute toxicity, chronic toxicity, or cosmesis. CONCLUSIONS Minimizing the V110 and V115 and limiting the V105 to ≤10% are useful dosimetric objectives to achieve excellent or good cosmesis following H-WBI. Acceptable toxicity and excellent cosmesis are achievable in women with large DoS or BV, provided techniques to maximize dose homogeneity are employed.