Initial Efficacy Results of RTOG 0319: Three Dimensional Conformal Radiation Therapy (3D-CRT) Confined to the Region of the Lumpectomy Cavity for Stage I/II Breast Carcinoma

Purpose/Objective(s) 

This prospective study examines the use of 3D-CRT to deliver accelerated partial breast irradiation (APBI). Reproducibility/ technical feasibility was the primary endpoint and has been previously published. This report focuses on the initial reporting of efficacy results, a secondary endpoint of the trial.

Materials/Methods 

Patients with AJCC 6th edition Stage I or II with lesions ≤3 cm, negative surgical margins, and up to 3 positive axillary nodes were eligible. Patients were required to have unifocal breast cancer and six surgical clips to delineate the margins of the lumpectomy cavity. Hormone and chemotherapy were allowed, with the chemotherapy having to be at least 2 weeks prior to starting or after ending 3D-CRT. The 3D-CRT was 38.5 Gy in 3.85 Gy/fraction delivered 2X/day. The clinical target volume (CTV) included the tumor bed plus a 10 - 15 mm margin. The planning target volume (PTV) included the CTV plus a 10 mm margin. Ipsilateral breast, ipsilateral nodal, contralateral breast, and distant failure (IBF, INF, CBF, DF) were estimated using the cumulative incidence method. Mastectomy-free, disease-free and overall survival (MFS, DFS, OS) were estimated using the Kaplan-Meier method.

Results 

Fifty eight patients were entered between August 2003 and April 2004. Fifty three patients are eligible and evaluable for efficacy. Two patients did not receive any protocol treatment and 3 patients were ineligible. The median age of patients was 61 years with the following characteristics: 45% tumor size <1 cm, 85% invasive ductal histology, 92% AJCC stage I, 66% post-menopausal; 83% no chemotherapy and 67% with no hormone therapy. Median follow-up is 3.5 years (1.6-4.2). Three-year estimates (95% CI) of efficacy are: IBF 6% (0%, 12%) [4% within field (0%, 9%)]; INF 2% (0%, 6%); CBF 0%; DF 6% (0%, 12%); MFS 92% (85%, 100%); DFS 88% (79%, 97%); and OS 96% (90%, 100%).

Conclusions 

Initial efficacy results using 3D-CRT to deliver APBI appear comparable to other experiences with similar, limited follow-up. However, additional patients, further follow-up and mature phase III data (i.e., RTOG 0413 trial) will be needed to establish the equivalence APBI to standard whole breast irradiation and the efficacy of this particular form of APBI.

Supported by RTOG U10 CA21661, CCOP U10 CA37422, and Stat U10 CA32115 grants from the NCI. This abstract's contents are the sole responsibility of the authors and do not necessarily represent the official views of the NCI.