Abstract P4-12-23: Institut Curie guidelines on breast target volume delineation for patients treated in lateral position

Abstract

Abstract Background and Purpose: Delineation of clinical target volumes (CTVs) is a weak link in radiation therapy (RT), and large inter-observer variation is seen in breast cancer patients. Several guidelines have been proposed, but most result in larger CTVs than based on conventional simulator-based RT. There is no consensual guideline for the delineation of the breast CTV in patients treated with alternative techniques as prone or lateral. The purpose of this study is to develop and describe the first delineation consensus-based guidelines defined by the radiation oncologists of the Institut Curie for the specific institutional technique of breast irradiation in lateral position. Materials and Methods: During the daily delineation in the Department of Radiation Oncology of the Institut Curie, the radiation oncologists specialized on breast cancer treatment sought consensus on delineation of CTV breast through dialogue based on cases. In all patients the breast was palpated and designed, initially in standing, then adjusted in lying position. One radiation oncologist delineated CTV on computed tomography (CT) scans of 5 to 20 patients. Totally 60 patients’ breasts were delineated after CT scan in treatment position. All patients were delineated in treatment position, skin markers were used to visualize the breast tissue. This delineation was followed by a discussion and an adaptation of the delineation between all doctors of the team. The consensus established between clinicians was discussed, corrected and improved. Results: The breast CTV is situated and delineated between pectoral muscle and 5 mm below the skin (dosimetric considerations), within the space outlined by skin markers, that showed the limits of the palpable breast tissue. In lateral position, two vessels were very useful: rami mammarii (from thoracica interna) and thoracica lateralis, both define the internal and external limits respectively. This is the first atlas proposed for delineation of the breast CTV for breast cancer treatment using alternative technique of breast irradiation (lateral). Future development is needed to develop the practical procedure of implementation and optimization of delineation using automatic software. Conclusion: The proposed guidelines are based on a consensus endorsed by a global radiation oncology group of breast cancer experts practicing this technique routinely. This atlas will be helpful for the volume definition in our daily practice of breast irradiation in lateral position and can open opportunities to develop atlases for alternative techniques as prone. Citation Format: Rebecca Msika, Magalie Robilliard, Alain Fourquet, Baptiste Porte, Youlia Kirova. Institut Curie guidelines on breast target volume delineation for patients treated in lateral position [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-12-23.