Anatomical, clinical and radiological delineation of target volumes in breast cancer radiotherapy planning: individual variability, questions and answers.

The purpose of the study was to evaluate the individual variability of anatomical and radiological delineation for breast cancer radiotherapy (RT) in preparation for new techniques and to propose practical solutions to improve delineation in everyday practice. In the first phase, a patient with stage T3N3M0 breast cancer and complete response after neoadjuvant chemotherapy was assessed by CT scan in the treatment position before RT. 11 radiation oncologists (5 breast cancer specialists and 6 residents) independently delineated the breast and lymph node (LN) regions before definition of target volumes. Organs at risk (heart, lung, thyroid and brachial plexus) were also delineated. All regions (breast, axilla, supraclavicular LN, infraclavicular LN and internal mammary chain) were delineated and compared in terms of volume. Comparative analysis was performed with Aquilab software. Differences in the clinical and radiological assessment were observed between the various radiation oncologists. Simplified rules of delineation were developed in the department. Using these rules, the second patient's CT was delineated by the same physicians and better results were observed. Simplified rules of delineation were developed. In conclusion, major differences in anatomical and radiological delineation for breast cancer RT were observed among the physicians. This study led to the development of written delineation protocols. The study is ongoing with evaluation of the dosimetric impact and definition of different target volumes.