Outcomes with Five Fraction Image-Guided Partial Breast Irradiation to Reduced Target Volumes

Abstract

The use of 5-fraction partial breast irradiation has been shown in a randomized trial to provide comparable rates of local control and reduced toxicities as compared to standard fractionation whole breast irradiation. The initial technique utilized a 2 cm expansion on the lumpectomy cavity (1 cm for clinical target volume [CTV], and 1 cm planning target volume [PTV]) without consistent image guidance (ex. cone beam computed tomography [CBCT]) or motion management recommendations. We present clinical outcomes using a 5-fraction image guided PBI technique (IG-PBI) to reduced target volumes for patients with early-stage breast cancer. A retrospective review of an IRB approved institutional registry was performed to identify patients treated with IG-PBI. A total of 258 patients with early-stage breast cancer (Stage 0-IIA) receiving IG-PBI were identified. Patients received a dose of 30 Gy in 5 fractions delivered daily or every other day. An expansion of 1 cm on the lumpectomy cavity was used for those patients using deep inspiration breath hold (DIBH) while an expansion of 1.5 cm was utilized for those not using DIBH. All patients received daily CBCT. Plans were delivered using intensity-modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) technique; while the prescription isodose line covered the PTV, the 26 Gy line was allowed to expand beyond the PTV. Kaplan-Meier analyses were used to assess rates of local control and survival. Patient demographics, stage, hormone therapy use, recurrence, mortality, and toxicity data were collected. Survival was analyzed with Kaplan-Meier curve. Median age at diagnosis was 67 years (range 40-87) with a median follow-up of 29 months (IQR 22-40). Forty-six (18%) patients had in situ disease, 200 (78%) patients T1 tumors, and 12 (5%) patients had T2 tumors. Two hundred thirty-four (91%) patients were White, 15 (6%) were Black, and 9 (4%) were other races. One hundred ninety-six (76%) patients received endocrine therapy, and 16 (6%) patients received chemotherapy. Thirty-two (12%) patients developed grade 1 dermatitis and no grade 2 events were observed. One (0.4%) patient had a cardiac event (aortic stenosis) 19 months after breast radiotherapy. At last follow-up, one (0.4%) patient had a local recurrence and one (0.4%) developed a distant metastasis, with no regional nodal failures. Overall, 4 (1.5%) patients had died, all due to other causes. At 3 years, locoregional control was 99.4%. Outcomes with IG-PBI demonstrate low rates of local recurrence and limited toxicity. The use of reduced target volumes is not associated with increased rates of local recurrence.