Status of postmastectomy radiotherapy in the United States: a patterns of care study

PURPOSE: The Patterns of Care Study performed this first known practice survey to establish a national profile of the delivery of postmastectomy radiotherapy (RT) in operable breast cancer. METHODS AND MATERIALS: A Patterns of Care Study research associate collected data from 55 randomly selected institutions. The survey data included 132 items describing the patient, pathologic features, and treatment course for patients with clinical Stage I, II, and IIIA breast cancer undergoing postmastectomy RT in 1998 and 1999. A multivariate analysis was performed to determine the impact of tumor factors and type of treatment facility on the radiation fields used. RESULTS: A weighted sample size of 13,720 was obtained from a sampling of 405 patient records. The mean tumor size was 3.5 cm, and the mean number of axillary nodal metastases was 4.55. Lymphatic vascular invasion was noted in 34%, microscopic skin or dermal lymphatic invasion in 16%, positive or close margins in 36%, and extracapsular nodal extension in 23%. Radiotherapy included the chest wall in all cases and the regional nodes in 78%. When nodal RT was delivered, it included a supraclavicular field, supplemental axillary field, and/or an internal mammary field in 98%, 46%, and 23% of cases, respectively. Chest wall and supraclavicular RT was delivered in >90% of instances with 6-MV photons to doses between 45 and 50 Gy. More variation was seen in the delivery of the axillary and internal mammary RT. On multivariate analysis, the presence of four or more positive nodes and treatment at a large-volume facility were the factors most frequently associated with the use of regional radiation fields. CONCLUSION: This Patterns of Care Study survey has demonstrated that breast cancer patients undergoing postmastectomy RT in 1998 and 1999 had a high proportion of factors associated with an increased risk of locoregional failure. The practice patterns established in this study provide a baseline for comparison with future survey results.