A phase I study of intraoperative radiotherapy for early breast cancer in Japan.

Background: The present study was designed to identify the optimal intraoperative radiotherapy (IORT) dose for early breast cancer in Japanese women.

Methods: A phase I study was designed using a scheme of dose-escalation from 19, 20, and 21 Gy at 90% isodose. The primary endpoint was early toxicity. Secondary endpoints were efficacy for a long period and late toxicity. Inclusion criteria were as follows: (1) tumor size <2.5 cm, (2) age >50 years, (3) surgical margin >1 cm, (4) intraoperative pathologically free margins, (5) written informed consent. Exclusion criteria were (1) contraindication to radiation therapy, (2) extensive intraductal component. Partial resection was performed with at least a 1-cm margin around the tumor. Radiation was delivered directly to the mammary gland employing a MOBETRON device. Toxicity was evaluated with the Common Terminology Criteria for Adverse Events (CTCAE), version 3.0.

Results: From December 2007 to September 2008, 9 patients were enrolled in the study. The first three patients received a radiation dose of 19 Gy. Within 3 months toxicity in each case was deep connective tissue fibrosis (grade 1: 2/3, grade 2: 1/3). The next three patients received a dose of 20 Gy and had toxicities of deep connective tissue fibrosis (grade 1: 3/3), hematoma (grade 1: 2/3), infection in the musculoskeletal soft tissue (grade 1: 2/3), and soft tissue necrosis (grade 2: 1/3). The final three patients received a dose of 21 Gy and had toxicities of deep connective tissue fibrosis (grade 1: 2/3), hematoma (grade 1: 1/3), infection in the musculoskeletal soft tissue (grade 1: 1/3), and soft tissue necrosis (grade 2: 2/3).

Conclusions: The IORT treatment was tolerated very well in Japanese women, and we now recommend the dose of 21 Gy.