Prone Accelerated Partial Breast Irradiation Comparing Five Versus Three Fractions for Early Stage Breast Cancer: A Multi-Institutional Prospective Randomized Trial

Accelerated partial breast irradiation (APBI) is a treatment option for favorable risk early stage breast cancer patients. Prior randomized trials have compared APBI (twice-daily, 10 fractions or daily, 5 fractions) vs whole breast irradiation. We report the early results of a prospective trial comparing 3 versus 5 fractions of prone APBI (NCT02755896). Eligible patients included postmenopausal women who completed breast conserving surgery, with pathologic T1N0 invasive breast cancer or grade 1-2 DCIS <2cm. Patients were randomized to Arm 1, 6Gy x 5 fractions daily or Arm 2, 8Gy x 3 fractions every other day. The planning target volume was the tumor bed plus a 1.5 cm margin. The primary endpoint was 2-year rate of grade 2-3 radiation fibrosis (LENT-SOMA). To test that the rate of fibrosis with Arm 2 is not >10% worse than the anticipated rate of 10% in Arm 1 (one sided α = 0.025, power = 80%), 142 patients are needed in each arm. Secondary endpoints were local control rates at 1, 2, and 3 years. Acute toxicity is measured using CTCAE v4.0 and compared between treatment arms (two-sided Fisher’s exact test). Patients at 2 academic hospitals were enrolled on this study. 192 patients signed consent; 16 patients withdrew or failed screening. 176 patients were randomized (88 per arm) and are available for analysis. Median age was 68 years (range 52-98). Median follow up was 8 months (range 1-50). There were no grade 3 breast or skin toxicities. Grade 1-2 toxicity was mainly dermatitis (Table). In Arm 1, there were 23 patients with grade 1-2 dermatitis and 6 patients with grade 1-2 pain/edema. In Arm 2, there were 16 patients with grade 1-2 dermatitis and 9 patients with grade 1 pain/edema. For the 34 patients evaluable at 2 years (20 in Arm 1, 14 in Arm 2), maximum fibrosis, telangiectasia and hyperpigmentation was grade 1 (Table). Grade 1 fibrosis occurred in 3 patients (8.8%) with similar rate between the 2 arms (1/20 vs 2/14). One of 176 patients (0.6%) developed an in-field invasive recurrence 2 years after radiation therapy and was treated with mastectomy.Abstract 1078; TableAcute ToxicityArm 1 (6GyX5) N = 88Arm 2 (8GyX3) N = 88pGrade 1 (%)Grade 2 (%)Grade 1 (%)Grade 2 (%)Dermatitis21 (23.9)2 (2.3)15 (17.0)1 (1.1)0.28Pain4 (4.5)1 (1.1)8 (9.1)0 (0)0.57Edema1 (1.1)0 (0)1 (1.1)0 (0)0.99Late Toxicity (2 yr)Arm 1 (6GyX5) N = 20Arm 2 (8GyX3) N = 14pGrade 1 (%)Grade 2 (%)Grade 1 (%)Grade 2 (%)Fibrosis1 (5.0)0 (0)2 (14.3)0 (0)0.55Telangiectasia1 (5.0)0 (0)0 (0)0 (0)1.00Hyperpigmentation0 (0)0 (0)1 (7.1)0 (0)0.42 Open table in a new tab