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 50.4 Gy in the CG, 40 Gy in MARA-1 (low risk of local recurrence), and 50 Gy in MARA-2 (medium-high risk of recurrence). The tumor bed total dose was 60.4 Gy (sequential 10 Gy electron boost), 44 Gy (concomitant 4 Gy boost), and 60 Gy (concomitant 10 Gy boost) in CG, MARA-1 and MARA-2 studies, respectively. Overall treatment time was of 32 fractions for CG (6.4 weeks); 16 fractions for MARA-1 study (3.2 weeks) and 25 fractions for MARA-2 study (5 weeks). Results: Three hundred and thirty two patients were included in the analysis. Dosimetric analysis showed Dmax and V107% reduction (p < 0.001) and Dmin 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, 6.6 weeks; MARA-1, 3.2 weeks; MARA-2, 5 weeks) with acceptable short-term toxicity