Three-Year Cosmetic Outcomes of a Phase I Dose Escalation Trial of 5-Fraction Stereotactic Partial Breast Irradiation for Early Stage Breast Cancer

Abstract

Noting that accelerated partial breast irradiation (APBI) has been shown to have acceptable oncologic outcomes with conflicting cosmetic results for early stage breast cancer following breast-conserving surgery (BCS) in phase III randomized trials, we explored stereotactic partial breast irradiation (S-PBI). Given S-PBI allows for the reduction of target volumes via the elimination of the traditional 1 cm PTV expansion used in APBI through the use of image guidance, we hypothesized that S-PBI would allow for safe dose escalation with acceptable cosmetic outcomes. A phase I dose escalation trial of S-PBI for early stage breast cancer following BCS was conducted. Women age ≥ 18 years with in-situ or stage I-II (AJCC 7) invasive breast cancer ≤ 3 cm following BCS with > 2 mm margins were treated with S-PBI in 5 fractions to a total dose of 30 to 40 Gy over 2.5 Gy increments. Patients and treating physicians scored overall cosmetic outcome at follow-up as excellent, good, fair, or poor with the global cosmetic score (GCS). An expert panel of breast specialists consisting of 2 radiation oncologists, 3 surgical oncologists, 1 radiologist, 1 medical oncologist, and 1 patient advocate independently rated serial photography for GCS and subdomain cosmetic outcomes. The McNemar test was then used to evaluate change of GCS from baseline to year 3 for patient-reported, physician-reported, and panel-reported scores independently. Of 75 patients enrolled and treated, cosmesis data was available for 74, 74, and 67 patients, for the patient-, physician-, and panel-reported scores, respectively. Median patient- and physician-reported cosmetic follow-up was 5, 5, 5, 3, and 3 years, and panel-reported was 4, 4, 4, 3, and 2 years for the 30, 32.5, 35, 37.5, and 40 Gy cohorts, respectively. For the overall cohort, rates of fair or poor GCS at baseline vs year 3 for patient-reported GCS were 13.7% vs 10.2% (10/73 vs 6/59; p = 0.5488), for physician-reported GCS were 4.1% vs 1.7% (3/74 vs 1/58; p = 0.5000), and for panel-reported GCS were 4.5% vs 2.4% (3/67 vs 1/41; p = 0.6250), with none differing by year 3. For individual dose cohorts, no statistical differences between the incidence of fair or poor cosmesis at baseline vs year 3 were found. Dose escalation of S-PBI from 30 Gy in 5 fractions to 40 Gy in 5 fractions for early stage breast cancer following BCS was not associated with a change in fair or poor cosmesis, with the majority of patients reporting good or excellent cosmesis both at baseline (>86%) and at year 3 of follow-up (>90%). S-PBI is a promising modality allowing for further hypofractionation of adjuvant breast radiation without detectable changes in cosmesis.