Chapter 51

The RTOG Cooperative Group celebrated its 40-year anniversary this year. However, the present Working Group is much younger, established in 1994 to focus on local-regional breast cancer issues involving radiation therapy questions. This chapter discusses those initiatives.

The concept of partial breast irradiation (PBI) was brought to the attention of the RTOG by Dr Robert Kuske, at one of the first meetings of the group. The idea was not new; Fentiman and colleagues had published a pilot study exploring the use of a small iridium 192 implant for breast cancer treatment in 1991. The local failure rate was higher than that of standard whole breast radiation, and the cosmetic outcome was inferior.1

However, both Kuske at the Ochsner Clinic and Vicini at William Beaumont Hospital pursued the idea of treating less than the whole breast after lumpectomy, utilizing low-dose-rate (LDR) and then high-dose-rate (HDR) brachytherapy when it became available. Based on their early, positive results,2,3 the RTOG Breast Group began to design the first cooperative group PBI trial, RTOG 95-17. This phase I/II trial specifically targeted small lesions (3 cm or less) with invasive ductal histology (IDC) only. Invasive lobular carcinoma was specifically excluded, as were patients with an extensive intraductal component to their IDC. This decision was made to exclude carcinomas characterized by microscopic extension beyond their clinically or radiographically apparent borders. In addition to the lumpectomy, an axillary node dissection was required, reflecting the surgical standard of the time. Women were eligible for entry in the trial with up to 3 nodes involved, although no extra capsular extension was allowed.

For women with an indication for systemic chemotherapy, the order of treatment was radiation first, followed by chemotherapy, with at least a 2-week interval from the completion of the radiation. The original accrual goal was 46 HDR cases and 46 LDR cases.

### RTOG 95-17: Accrual and Results

The study opened in 1997 and completed accrual in 2000; 100 women were accrued, with just 1 excluded from analysis because she underwent a sentinel node biopsy only. Reflecting changing trends in brachytherapy, 66 cases were accrued to the HDR arm and 33 to the LDR arm. Of interest, only 11 RTOG institutions placed cases on this protocol, reflecting the high level of skill required of the oncologist to perform these implants.

This study set a high standard for quality assurance (QA), requiring a credentialing process for each participating center before enrolling cases. In addition, each case was "rapidly reviewed" by the principal investigator within 24 hours of catheter placement. For 8 patients, this led to revisions in their implant dosimetry prior to treatment. The success of the quality assurance program is evidenced by 96% of cases meeting specified requirements and only minor variation in the other 4% on final analysis.4 This plan formed the foundation for quality assurance in the large phase III ...

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