Defining Target Volumes in Breast Cancer Radiation Therapy for the Future: Back to Basics.

There is considerable evidence that for many node-positive breast cancer patients, local regional radiation therapy after mastectomy, or regional radiation therapy in addition to breast treatment after lumpectomy, results in improved local control, a more modest but consistent reduction in distant metastases, and absolute improvement in breast cancer survival (1, 2). On the other hand, there is similar substantial evidence that the use of local regional radiation therapy can come with the price of permanent toxicity such as lymphedema (2), and even more serious consequences like cardiac-related mortality (3). It would seem then that this critical balance of potential survival benefit and toxicity risk would be an ideal setting for using advanced radiation treatment planning to conform dose to targets and avoid normal tissues, thereby maximizing the therapeutic ratio. It was with this in mind that members of the Breast Cancer Committee within the Radiation Therapy Oncology Group (RTOG) sought to systematically evaluate advanced treatment planning for breast cancer by integrating questions about its feasibility and effect on outcomes into the radiation therapy treatment arms of clinical trials asking breast cancer questions. However, to transition from planning breast cancer radiation therapy based on a standardized field arrangement to a patient-specific, CT-based, 3-dimensional conformal radiation therapy (3D-CRT) planning, some idea of the anatomic boundaries of the regions of interest were necessary so that targets could be generated and doseevolume analysis (DVA) could be done. In particular, use of DVA was keenly anticipated as an important quality control and analysis tool in breast cancer