Phase I–II studies on accelerated IMRT in breast carcinoma: Technical comparison and acute toxicity in 332 patients

Abstract 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.