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.
Read full abstract
Sep 6, 2021
Rachita Dhurat + 2
Open Access