A prospective phase I comparison of toxicity and cosmesis outcomes of single-fraction IORT and hypofractionated radiotherapy with IORT boost in early-stage breast cancer.

Radiation therapy is proven to reduce local recurrence in patients with early-stage breast cancer. To reduce toxicity, treatment time, and improve accuracy, intraoperative radiation therapy was used as definitive treatment or as a boost. The study's objective was to compare the short-term toxicity and cosmesis of single-fraction (SF) IORT and hypofractionated radiotherapy with IORT boost (HfB) given as definitive treatment.Between March 2011 and December 2013, 57 patients aged 45-91 years and 24 patients aged 43-83 years (total n = 81) with Stage 0-II were treated with SF or HfB (Mobetron, IntraOp Medical, Sunnyvale, CA). For SF treatment, 21 Gy was delivered using 4.5-6 cm applicators with electron energies from 6 to 12 MeV. For HfB, an intraoperative boost of 10 Gy was delivered using 4-7 cm applicators with energies from 4 to 12 MeV followed by whole-breast radiation with 40.5 Gy over 15 fractions. Toxicity was assessed at 2 weeks, 6 months, and 12 months per Radiation Therapy Oncology Group acute skin toxicity criteria and cosmesis.At 12 months, SF and HfB were well tolerated by all patients with no Grade 3+ toxicity. At 1 year, Grade-2 toxicity was resolved. Ninety-eight percent of SF patients and ninety percent of HfB patients had 0-1 grade toxicity. In the SF and HfB groups, 100% of patients had excellent or good cosmesis at 12-month followup interval. The SF exhibited a more favorable cosmesis with a higher percentage of excellent scores compared with HfB (80.4% vs. 45%; p = 0.0033).After breast conservation surgery, SF or HfB may be an option for patients with early-stage breast cancer compared to conventional external beam radiotherapy.