Phase I-II studies on accelerated IMRT in breast carcinoma: technical comparison and acute toxicity in 332 patients.

BACKGROUND AND PURPOSE: To evaluate the results in terms of dosimetric parameters and acute toxicity of two clinical studies (MARA-1 and MARA-2) on accelerated IMRT-based postoperative radiotherapy. These results are compared with historical control group (CG) of patients treated with "standard" 3D postoperative radiotherapy. MATERIALS AND METHODS: Prescribed dose to the breast was 50.4Gy in the CG, 40Gy in MARA-1 (low risk of local recurrence), and 50Gy in MARA-2 (medium-high risk of recurrence). The tumor bed total dose was 60.4Gy (sequential 10Gy electron boost), 44Gy (concomitant 4Gy boost), and 60Gy (concomitant 10Gy boost) in CG, MARA-1 and MARA-2 studies, respectively. Overall treatment time was of 32 fractions for CG (6.4weeks); 16 fractions for MARA-1 study (3.2weeks) and 25 fractions for MARA-2 study (5weeks). RESULTS: Three hundred and thirty two patients were included in the analysis. Dosimetric analysis showed D(max) and V(107%) reduction (p<0.001) and D(min) improvement (p<0.001) in the PTV in patients treated with IMRT. Grade 2 acute skin toxicity was 33.6%, 13.1%, and 45.1% in the CG, MARA-1, and MARA-2, respectively (p<0.001), and grade 3 acute skin toxicity was 3.1%, 1.0%, and 2.0%, respectively. Similarly, larger PTV and use of chemotherapy with anthracyclines and taxanes were associated with a greater acute toxicity. With a median follow-up of 31 months, no patients showed local or nodal relapse. CONCLUSIONS: A simplified step and shoot IMRT technique allowed better PTV coverage and reduced overall treatment time (CG, 6.6weeks; MARA-1, 3.2weeks; MARA-2, 5weeks) with acceptable short-term toxicity.