Daily Fractionation of External Beam Accelerated Partial Breast Irradiation to 40 Gy Is Well Tolerated and Locally Effective

Abstract

Purpose: Most studies examining accelerated partial breast irradiation (APBI) have used twice-daily fractionation. Cosmesis with this approach has produced mixed results, and the optimal fractionation scheme remains unknown. We sought to evaluate the safety and efficacy of APBI with a total dose of 40 Gy in 10 daily fractions.

Methods and materials: Between 2010 and 2014, we prospectively enrolled 106 patients to receive APBI after lumpectomy for invasive or in situ node-negative breast cancer. Radiation was administered via 3-dimensional conformal techniques.

Results: The median age was 62 years (range, 39-85), and all patients underwent APBI per protocol. With a median follow-up of 58 months, we evaluated patient-reported local toxicity and recurrence outcomes. Of 106 patients, 16 (15%) experienced grade ≥2 skin toxicity. The most common significant toxicities were acute cutaneous changes at 4 to 9 weeks after radiation therapy, including grade 2 erythema in 2 patients (1.8%) and skin color changes in 4 patients (3.8%). Only 2 instances of grade 3 toxicity were reported, including 1 patient with acute moist desquamation after radiation therapy and another with fibrosis at 2 years. Planning target volume and breast V₂₀ were significantly predictive of skin/subcutaneous toxicity, with evidence that limiting breast V₂₀ to <45% may improve tolerability. Overall, 3 breast cancer recurrences arose: 1 local recurrence in the original quadrant (3 years after APBI), 1 in a different ipsilateral quadrant (5 years after APBI), and 1 with distant disease 2 years after APBI.

Conclusions: In an appropriately selected group of patients with early stage breast cancer, APBI to a dose of 40 Gy in 10 daily fractions was well tolerated, with most patients (99%) reporting excellent/good cosmesis. Planning target volume and breast V₂₀ should be carefully constrained to limit local morbidity. Longer follow-up will be needed to establish efficacy and subsequent local recurrence rates.

Fig 1.

Dose-response curves for the two treatment planning metrics found to significantly predict skin toxicity (PTV: upper left; Breast V₂₀: lower left), and the dose-response curve combining these metrics (right). Various parameterizations of PTV, Breast V₂₀, or the combination thereof and the resulting rate of skin toxicity according to the predictions are shown in the upper left insets; these may be used as example thresholds to further reduce the rate of skin toxicity upfront. Note: Associated AUCs are inserted in the upper right corners; Predictions: solid line; Observations: (error bars: 95% Binomial confidence intervals).