ESTRO 38 Abstract book

S49 ESTRO 38

is delivered with a gated beam on threshold of 3mm (fig.1). A spotlight CBCT is acquired at the end of treatment to confirm patient positioning and OSMS accuracy (fig.2). CBCT shifts, DIBH times and overall treatment times were measured.

system that captures and compares images of a patient's topography to a DICOM-formatted external contour could be broken by the gantry motion during the VMAT session. To increase the accuracy of intra-fraction motion management and to avoid this break, we intend to compare the use of two types of ROIs in VMAT radiotherapy for breast cancer treatment. Material and Methods From November 2017 to march 2018, sixty breast cancer patients who underwent whole breast radiotherapy (WBRT) with VMAT treatment were selected for this study. CBCT were performed at the 1 st , 2 nd ,3 rd day of the treatment, and then weekly. Patients were divided into two groups of thirty. Group one (G1) was positioned with the aid of AlignRT using an isocentric region of interest (ROI) containing the treated breast and the upper part of the abdomen (limited ROI). In group two (G2), patients were also positioned with AlignRT with a ROI containing the treated breast and half part of the contralateral breast (extensive ROI). For both groups, extra-treatment sites’ ROIs were the same: homolateral arm, neck and head position. All the fractions for each patient were consecutively analyzed. Results A break in the intra-fraction motion management with AlignRT was noticed in 283/721 (39%) sessions using limited ROIs (G1), versus 52/702 (7%) using extensive ROIs (G2). In G1, 3/30 patients could achieve their treatment without any break versus 18/30 in G2. Conclusion We demonstrated that intra-fraction motion management with AlignRT in VMAT for breast cancer is reproducible and accurate thanks to a modification of isocentric ROIs, and allows the use of 3D surface imaging system in deep- inspiration-breath hold with VMAT technique in our institution. OC-0096 Implementation of DIBH for gated IMRT of left sided breast cancer using optical surface guidance N. Gomes 1,2 , A.M. Furtado 1 , M.D.G. Coelho 1,2 , M. Possanzini 3 , J. Morales 1 , C. Greco 1 1 Fundaçao Champalimaud, Radiation Oncology, Lisboa, Portugal ; 2 Mercurius Health, Radiation Oncology, Lisboa, Portugal; 3 Azienda Ospedaliera G. Brotzu, Radiation Oncology, Cagliari, Italy Purpose or Objective To describe the implementation of a workflow for treating left breast cancer patients with hypofractionated IMRT in DIBH using SGRT (Surface Guided Radiotherapy). This is known to reduce heart dose and therefore cardiotoxicity risk. Material and Methods 24 patients with left sided breast cancer confined to the breast were selected. First, they had a training session on the Linac. The procedure was explained and the breathing amplitude and reproducibility were verified using OSMS (Optical Surface Monitoring System). Patients had to maintain DIBH for a minimum of 25s (mean time for a treatment field delivery). Treatment isocenter was defined to allow spotlight CBCT acquisition in DIBH to confirm lung expansion. Suitable patients then had 2 planning CTs (Free Breathing (FB) and DIBH). As OSMS is not installed in the CT room, spotlight CBCT and DIBH planning CT were merged to confirm reproducibility. Treatment plans using IMRT (2.7Gy to whole breast and 3.2Gy to an integrated boost) in 15 fractions were planned for both CTs to validate DIBH’s advantage. Patients selected to be treated with DIBH had their setup confirmed with CBCT in FB before each treatment. OSMS was used to automatically perform shifts to DIBH isocenter. Spotlight CBCT was performed to avoid centring the couch while allowing continuous monitoring, prevent collisions, confirm lung expansion and heart position. If shifts within departmental tolerances (<3mm), treatment