Intensity Modulated Radiation Therapy (IMRT) With Simultaneously Integrated Boost Shortens Treatment Time and Is Noninferior to Conventional Radiation Therapy Followed by Sequential Boost in Adjuvant Breast Cancer Treatment: Results of a Large Randomized Phase III Trial (IMRT-MC2 Trial)

Purpose: In the modern era, improvements in radiation therapy techniques have paved the way for simultaneous integrated boost irradiation in adjuvant breast radiation therapy after breast conservation surgery. Nevertheless, randomized trials supporting the noninferiority of this treatment to historical standards of care approach are lacking.

Methods: A prospective, multicenter, randomized phase 3 trial (NCT01322854) was performed to analyze noninferiority of conventional fractionated intensity modulated radiation therapy with simultaneous integrated boost (IMRT-SIB) to 3-D conformal radiation therapy with sequential boost (3-D-CRT-seqB) for breast cancer patients. Primary outcomes were local control (LC) rates at 2 and 5 years (noninferiority margin at hazard ratio [HR] of 3.5) as well as cosmetic results 6 weeks and 2 years after radiation therapy (evaluated via photo documentation calculating the relative breast retraction assessment [pBRA] score [noninferiority margin of 1.25]).

Results: A total of 502 patients were randomly assigned from 2011 to 2015. After a median follow-up of 5.1 years, the 2-year LC for the IMRT-SIB arm was noninferior to the 3-D-CRT-seqB arm (99.6% vs 99.6%, respectively; HR, 0.602; 95% CI, 0.123-2.452; P = .487). In addition, noninferiority was also shown for cosmesis after IMRT-SIB and 3-D-CRT-seqB at both 6 weeks (median pBRA, 9.1% vs 9.1%) and 2 years (median pBRA, 10.4% vs 9.8%) after radiation therapy (95% CI, -0.317 to 0.107 %; P = .332). Cosmetic assessment according to the Harvard scale by both the patient and the treating physician as well as late-toxicity evaluation with the late effects normal tissues- subjective, objective, management, analytic criteria, a score for the evaluation of long-term adverse effects in normal tissue, revealed no significant differences between treatment arms. In addition, there was no difference in overall survival rates (99.6% vs 99.6%; HR, 3.281; 95% CI: -0.748 to 22.585; P = .148) for IMRT-SIB and 3-D-CRT-seqB, respectively.

Conclusions: To our knowledge, this is the first prospective trial reporting the noninferiority of IMRT-SIB versus 3-D-CRT-seqB with respect to cosmesis and LC at 2 years of follow-up. This treatment regimen considerably shortens adjuvant radiation therapy times without compromising clinical outcomes.