ESTRO 2020 Abstract book

S1078 ESTRO 2020

patients as well as 47 left sided breast cancer patients treated in DIBH were evaluated. Results From the initial 19 FB patients with 285 fractions, 267 of these fractions (94%) had shifts in all directions which were within our 5mm tolerance. From the initial 17 DIBH patients, 277 of 296 fractions (94%) had shifts within tolerance. The first additional data collection was done for DIBH 1 year after implementation, following staff changes and included 15 patients (195 fractions). This showed that only 85% of fractions had shifts within our 5mm tolerance, a result with unacceptable decrease in accuracy. Due to this, extra staff training consisting of multiple presentations, as well as hands on workshops were performed. After 4 months, a 3rd evaluation was completed based on 8 FB (90 fractions) and 15 DIBH (235 fractions) patients. After training, the accuracy had risen again to 94% of FB fractions and 96% of DIBH fractions being within tolerance after set up with SGRT. In total over all data collections, mean post-match shift based on imaging was -1.2 ±2.0 mm, 0.3 ±2.2mm, and -0.9 ±2.0mm for FB and -0.8 ± 1.7mm, 0 ± 2mm, and 0.4 ± 1.2mm for DIBH in the VRT, LNG and LAT directions respectively. Imaging was then reduced from daily MV images (20) to weekly images (8). Conclusion The data shows that SGRT setup is accurate within 5mm in over 96% of fractions of DIBH and 94% for free breathing breast cancer patients. Staff training plays a critical role on the successful implementation of patient positioning using an SGRT system. Based on this evaluation, imaging policy was changed from daily imaging to daily patient positioning using SGRT with setup imaging performed for the first 3 fractions and subsequently only once a week to reduce both excess dose to the patient and treatment time on the Linear accelerator. PO‐1840 Introduction of an RT consult to assess bladder size prior to planning CT scan for prostate patients W. Goldshaker 1 , A. Aggarwal 1 , T. Guerrero-Urbano 1 , S. Purpose or Objective At Guy’s & St Thomas’ NHS Foundation Trust, 400 prostate patients are referred for radical radiotherapy per year. Standard departmental practice is to ensure that the bladder is sufficiently full to push the small bowel out of the planned target volume facilitating meeting planning dose constraints. To achieve this the patient is required to drink 350ml of water and wait 45 minutes. An ultrasound is performed to assess bladder volume prior to receiving their radiotherapy CT planning scan. If the volume is <200ml, the patient is sent home to hydrate for 48 hours. This introduces a delay into the patient pathway, reduces scanner capacity and causes inefficiencies in the radiotherapy service. A Pre-Radiotherapy Consultation was introduced to discuss hydration with the patient and assess their bladder volume. It was hypothesised that this appointment would reduce the number of patients not being scanned due to a small bladder volume. Material and Methods A retrospective audit was carried out to assess the bladder volumes of prostate patients who came for CT scan. It demonstrated that, over a 6 week period, for 21% of patients, their CT scan was delayed as their bladder volume was deemed too small. A pilot study was conducted which involved booking a consultation 48 hours prior to the CT scan. During this visit, the patient was given standard pre-CT information including explanation of CT procedure and consent confirmation. The rationale for a full bladder was explained, hydration advice given, and the consequences of having an insufficient bladder volume at Harris 1 , S. Hughes 1 , S. Morris 1 , V. Mullassery 1 1 Guy's & St. Thomas' NHS Foundation Trust, Radiotherapy, London, United Kingdom

multi-target (SIMT) SRS at UPMC Hillman Cancer San Pietro Hospital, Rome, were retrospectively evaluated. All plans were created using a commercial software (Brainlab Elements Multiple Brain Mets SRS, version 1.5) and the treatments were performed with Novalis Tx (Brainlab AG, Munich, Germany and Varian, CA, USA). In the treatment room, the accuracy of patient set-up was assessed by the integrated ExacTrac kV X‐Ray 6D imaging system (version 5.5, Brainlab, Munich, Germany). Variations of target positioning and coverage due to translational and rotational residual isocenter errors were evaluated using the Velocity AI software (version 3.0.2; Varian Medical Systems, Palo Alto, CA, USA). During the treatment, stereoscopic X-Ray imaging was repeated at different times to verify and correct the isocenter position.Brain control and overall survival were estimated by Kaplan- Meier method calculated from the time of SRS Results Fourteen patients were treated for 3-6 metastases and 12 patients for > 6 metastases with a median dose of 22 Gy and a GTV-to-PTV margin of 1 mm. The median gross total volume (GTV) was 0.29 cm 3 and the median planning target volume (PTV) was 0.47 cm 3 . With a median clinical follow- up of 9 months (range 2-29 months), the 1-year survival was 67% and local control was 86%. No grade 3 neurological toxicity was observed. A loss of target coverage, defined as a variation of V95 > 5% or resulting in a V95 < 95%, occurred in 25 PTVs (10 patients). Using a GTV-to-PTV margin of 1 mm, a GTV coverage was maintained for all treated lesions. Based on 52 ExacTrac image registrations, 8 isocenter positionings in 6 patients were out of tolerance (> 0.5 mm for translations > 0.5° for rotations) requiring SIMT DCA SRS represents a fast and effective approach for patients with up to 10 brain metastases. With setup and intra-fraction positioning based on the ExacTrac X-Ray 6D imaging system, the impact of residual translational and rotational errors on geometric and dosimetric deviations of treated targets is modest. PO‐1839 Implementation of image reduction for DIBH/FB breast patients following evaluation of an SGRT device M. Heinitz 1 , S. Perryck 1 , C. Linsenmeier 1 , S. Tanadini- Lang 1 , G. Matthias 1 , I. Pytko 1 , M. Zamburlini 1 , A. Moreira 2 1 University Hospital Zürich, Radiaton Oncology, Zürich, Switzerland ; 2 University Hosptial Zürich, Radiaton Oncology, Zürich, Switzerland Purpose or Objective Decrease of imaging dose as well as treatment time of breast cancer patients is of high interest in modern radiation therapy. This study aimed at evaluating the setup accuracy of an SGRT (Surface Guided Radiation Therapy) system for the treatment of breast cancer patients in DIBH and free breathing as well as exploring workflow changes to reduce imaging for this particular patient group. Material and Methods SGRT was initially implemented for free breathing (FB) patients (19 patients evaluated) and DIBH patients (17 patients). Patients were positioned supine on the breast board using SGRT. The patients were positioned until all pre-shift deltas displayed on the SGRT systems were within 1mm. For DIBH patients, after the free breathing surface was used to establish a vertical baseline, the DIBH surface was used to further position the patients. Before treatment, MV imaging was performed to verify the patient’s position, and shift values from imaging were recorded. Vertical (VRT), Lateral (LAT) and Longitudinal (LNG) shift values within 5mm were considered within our tolerance. Follow up evaluations were completed at time points over the next 2 years. In total 27 FB breast cancer corrections. Conclusion