Evaluation of a software for automatic delineation of the mammary gland and organs at risk in patients treated for breast cancer in lateral position.

PURPOSE OF THE STUDY: The purpose of this study was to assess the potential for improvement of routine breast and organs at risk contouring in patients treated in the lateral decubitus position using Workflow Box™ (Mirada Medical™, UK) automatic contouring software. MATERIALS AND METHODS: Automatic contouring of the breast by this software is currently based on an atlas created from isodoses representing 95% of the prescribed dose in a population of patients previously treated at institut Curie. Forty cases of breast cancer (20 right breasts and 20 left breasts) were contoured by three radiation oncologists specialized in breast cancer, allowing the creation of a new atlas in the automatic contouring software. This study assessed the quality of contouring in 20 patients (ten right breasts and ten left breasts) by comparing manual contouring performed by the expert radiation oncologists (reference) with those generated by the old and new atlases developed at Institut Curie. The accuracy of contouring was assessed by overlap volume and the associated standard deviations. RESULTS: Breast contouring based on the new atlas and by radiation oncologists presented a mean overlap of 0.80±0.09 for the right breast and 0.81±0.06 for the left breast. By comparing volumes of interest contoured by radiation oncologists and those obtained from the old atlas, mean overlap volumes were 0.75±0.08 and 0.74±0.13 for the right and left breasts, respectively. Twenty cases (ten right breasts and ten left breasts) used to create the new atlas were also reprocessed by this same atlas in order to assess the quality of automatic contouring of the breast when the case was already known to the software. The mean overlap volume in this case was 0.84±0.08 for the right breast and 0.83±0.06 for the left breast. Finally, after automatic contouring of organs at risk by means of the new atlas, the mean overlap volume was 0.87±0.04 for the heart and 0.93 for each lung (±0.05 for the right lung and±0.04 for the left lung). CONCLUSION: Workflow Box™ automatic contouring software, based on our new atlas provides reliable and clinically relevant organs at risk and breast contouring. The contours proposed by the software from the new atlas were better than those obtained with the previous atlas based on 95% isodoses obtained from old treatment plans. This software has therefore become more efficient, justifying its use in routine clinical practice for breast cancer contouring in patients treated in the lateral decubitus position. Investigations are currently underway to develop a fully automated process to ensure reliable, robust and operator-independent contouring and breast cancer treatment dosimetry in the lateral decubitus position. Promising preliminary results have already been obtained.

Institut Curie guidelines on breast target volume delineation for patients treated in lateral position.

PURPOSE: To develop guidelines for and describe the delineation of breast for patients treated in lateral position and to transform this three-dimensional technique based on the virtual simulation to volume-based modern intensity-modulated irradiation technique. MATERIAL AND METHODS: In our department, during the daily delineation, radiation oncologists specialized in breast cancer treatment sought consensus on the delineation of clinical treatment volume of the breast through dialogue based on cases. A radiation oncologist delineated clinical treatment volumes on CT scans of five to 20 patients, followed by a discussion and adaptation of the delineation between all radiation oncologists of the team. The consensus established between clinicians was discussed, corrected and improved. All patients were delineated in treatment position; skin markers were used to visualize the breast tissue after careful palpation. RESULTS: Breast clinical treatment volume was situated and delineated between pectoral muscle and 5mm below the skin (dosimetric considerations), within the space outlined by skin markers, that showed the limits of the palpable breast tissue. In lateral position some vessels were very useful to define the limits as rami mammarii (from thoracica interna) for the internal one and thoracica lateralis for the external. This is the first atlas proposed for the delineation of the breast clinical treatment volumes for breast cancer using alternative technique of breast irradiation (lateral). CONCLUSION: This atlas will be helpful for the volume definition in our daily practice of breast irradiation in lateral position and can open perspectives to develop also atlases for other alternative techniques as treatment in prone position.