ESTRO 2020 Abstract book

S77 ESTRO 2020

CT simulation. While positioning the patient according to skin marks and in-room lasers is the current standard practice, this method suffers from potential inaccuracies due to patient rotations, which are hardly detectable and accounted for, and misalignments of body regions, where no skin marks are drawn on. The same precision as with spatial lasers is achieved using SGRT-based positioning. For some body regions, SGRT has the potential to decrease the number of CBCT-based setups, resulting in the reduction of unnecessary radiation exposure to the patient, if it is assured that setup uncertainties are in the same range as CBCT positioning with SGRT. For treatment sites in the abdominal or pelvic region, this seems not to be the case: For example bladder and/or rectum filling set a limit to patient (or tumor) position using solely the surface as a surrogate. In addition, the accuracy of SGRT patient positioning decreases from cranial to abdominal regions (as well as for laser-based patient setup). The tube-like shape of (most) abdominal regions causes any registration algorithm to be less effective and reliable. Using internal organs or bones (and therefore techniques such as 2D, 3D, 4D MV/kV imaging, ultrasound, or marker tracking, etc.) in these cases cannot be neglected. With a (relatively) novel technique like SGRT, there remain many potential improvements in the workflows. One is that (even close to unnoticeable) time delays in patient setup can decrease the acceptance of therapists. In addition, more focus must be drawn upon staff training. As most commercially available systems are standalone systems, there is a lack of integration in the clinical workflows (e.g. CBCT-based positioning and 6DoF couch tops). The positioning of abdominal/thoracic (internal) tumor sites is one of the major future applications for SGRT, as internal-external correlation models are still missing on a broad basis. The selection of the region-of-interest (ROI) is another research topic, as there are no clear recommendations on which part of the surface has the highest impact on the patient position (for example the position of the upper arms during breast radiation). In general, SGRT helps to improve patient safety, increases the initial positioning accuracy (compared to laser-based patient setup), and could eventually replace (some) additional CBCT positioning. An extra effort in additional training, QA procedures, and time (and staffing) costs has to be made prior and during the use of any SGRT system and technique. SP-0148 Estimating the dosimetric effects of intrafraction motion: the role of surface imaging M. Kügele 1 1 Skåne University Hospital, Department of Hematology- Oncology and Radiation Physics, Lund, Sweden Abstract text Surface guided radiotherapy (SGRT) is an excellent example that show consensus with the ESTRO theme 2020 ‘Translating research and partnership into optimal health’. Close partnership between the university and industry has led to clinical SGRT implementations around the world. The use of optical surface scanning for patient positioning, monitoring during beam delivery and deep inspiration breath hold has increased rapidly in both the US and Europe the over last years. The real time surface imaging has the capability to halt the treatment if the patient motion exceeds a specified tolerance, which can be individually pre-set, but also diagnose specific. For this reason, two clinical applications have been widely adopted: deep inspiration breath hold (DIBH) and frameless SRS. Recent developments of the SGRT technology also provides motion monitoring for deep- gantry linacs. Treatment in deep-inspiration breath hold for left sided breast cancer can enable a decreased absorbed dose to organs at risk (OARs) while maintaining the target

or systemic BM treatment due to BM presentation. These patients are not necessarily at the end of the course of their disease and deserve attention to their neurocognitive outcome. HA-WBRT showed its cognitive preservation ability in three randomized trials and in a meta-analysis, as well as no additional toxicity and an acceptable recurrence rate in the HA area. Taken together, these data should lead to the routine use of HA when considering WBRT. SP-0146 Against the motion: This house believes that hippocampus avoiding WBI is the current standard of care C. Le Pechoux 1 , A. Levy 1 , A. Botticella 1 , O. Henry 2 , G. Auzac 2 , S. Bolle 1 , F. Dhermain 1 1 gustave Roussy Cancer Campus, Radiation Oncology, Villejuif Cedex, France ; 2 gustave Roussy Cancer Campus, Radiation Oncology Physics, Villejuif Cedex, France Abstract text Because of advances in the management of several solid tumours such as NSCLC, breast cancer, melanoma, the risk of developing brain metastases (BM) seems to increase as survival is prolonged. Their management represents a real challenge because Symptomatic BM can cause life- threatening symptoms and serious impairment of quality of life. In the last 15 years, there has been development and widespread use of stereotactic radiotherapy (SRT), but this concerns a subgroup of patients who have a limited number of brain lesions, for whom brain SRT and/or surgery can be proposed. This strategy provides better results than whole-brain irradiation (WBI) with median survival exceeding 12 months. WBI is still regarded as standard treatment for multiple symptomatic BM, not accessible to SRT even though a randomised trial does not seem to support the use of this approach versus best supportive care in NSCLC. There is strong concern about the toxicity of such treatment. Acute toxicity is generally manageable but long-term sequelae such as neurocognitive toxicity and ataxia, are deleterious to the quality of life of patients. There are areas of active research that hold great potential to reduce the risk of neurocognitive decline after WBI such as hippocampal- sparing radiotherapy and the use of neuroprotective agents. As neurocognitive toxicity from WBI related to damage to neural progenitor cells in the subventricular zone and hippocampus and the induction of inflammation in the brain, several studies have been performed assessing hippocampus avoiding irradiation, considering that BM in the hippocampal region seem rare (about 5%), Promising results have been reported in patients having undergone WBI to treat BM. Another challenging area is evaluating prophylactic cranial irradiation with hippocampus avoidance, with contrasting preliminary results. The cause of radiation injury to the brain is likely to be multifactorial, and reducing radiation dose to the hippocampus may not be the only way to reduce neurotoxicity. Furthermore we need more mature results to conclude that it should the new standard of care. SP-0147 Surface imaging for patient positioning: current status and scope for improvements P. Freislederer 1 1 University Hospital- LMU Munich, Department of Radiation Oncology, Munich, Germany Abstract text Surface guided radiation therapy (SGRT) is a technique which uses optically visible light (and potentially other sources, such as thermal imaging) in order to position the patient during treatment according to the position during Symposium: Surface guided radiation therapy

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