ESTRO 2021 Abstract Book

S541

ESTRO 2021

increased homogeneity of PTV coverage and reduction of hot spots • Compatible with modulated techniques in particular IMRT(only 1 pt with VMAT) • Easy handling and integration in daily practice • Reduction of skin markings

Our next steps taken: •

Going marker free: more precision and patient comfort (3 of 120 pts still needed skin marks) • Applying SGRT to right sided patients in supine position with DIBH to achieve a standard work flow for all breast cancer pts • Apply SGRT to all pts with planning CT based RT Take home messages: • Optimal sparing of normal tissue (heart and lung) with SGRT in DIBH • Compatible with modulated techniques (IMRT or VMAT) • Enhanced patient convenience (no skin markings or tattoos) • Standard workflow for left and right sided breast tumours

Debate: Is it primetime for stereotactic radiotherapy for localised high-risk prostate cancer?

SP-0677 For the motion T. Zilli 1 1 Geneva University Hospital, Radiation Oncology, Geneva, Switzerland

Abstract Text Ultrahypofractionation using stereotactic body radiotherapy (SBRT) is an advanced technique delivering large radiation doses in ≤5 treatments with cost and patient convenience advantages. Based on the promising tolerance and efficacy results of SBRT in prostate cancer patients with low- or intermediate-risk disease, SBRT indications have been enlarged during the last years to patients with high-risk disease. According to 2020 National Comprehensive Cancer Network guidelines, SBRT can be considered for patients with high-risk prostate cancer, as long as they have social or medical hardships that prevent longer courses of radiation therapy. Although strong level I evidence is still missing and long-term follow-up limited, available data suggest favorable toxicity and promising efficacy profile of ultrahypofractionated schedules for high-risk prostate cancer patients. Reported disease control rates compare favorably with dose escalated trials using brachytherapy boost or standard fractionated external beam radiotherapy, while toxicities rates seems to be lower or comparable to moderate hypofractionated schedules thanks to the use of very conformal radiotherapy techniques. Accurate patient selection, implementation of elective nodal SBRT irradiation and optimization of systemic treatments will probably improve disease outcome of these patients. Moreover, technological advances, such as direct magnetic resonance imaging–guided radiotherapy, will help to improve the precision of SBRT treatments. Waiting for results of ongoing prospective and randomized trials, this presentation will focus on potential future applications of this treatment strategy as alternative to conventional radiotherapy among patients with high-risk prostate cancer. SP-0678 Against the motion A. Tree 1 1 The Royal Marsden Hospital and the Institute of Cancer Research, Urology, London, United Kingdom Abstract Text Over the last decade fractionation in prostate cancer has changed, and most patients are now offered moderate hypofractionation (2.5Gy-3.5 Gy per fraction) rather than the historic 2 Gy per fraction. Concurrent with this, clinical evidence is growing to support the effectiveness of 5 fraction SBRT. Although definitive Level one evidence supporting the equivalence of SBRT for low and intermediate risk prostate cancer is lacking, it is expected that long term outcomes will be similar. However currently this data is lacking for higher risk and more advanced prostate cancer. Whilst the alpha/beta ratio may be similar regardless of Gleason grade, the small margins necessary for safe SBRT may miss microscopic disease and compromise cure rates. Indeed some series show a worrying trend to unfavourable recurrence rates after SBRT for higher risk disease. With many available examples of “medical reversal” in the literature, where treatments considered to be effective were subsequently proven to be no use or even harmful, we wish to avoid falling into this trap with SBRT. This talk will discuss the extent of available knowledge in 2021, both in terms of biochemical control and in terms of side effects and highlight where data may be forthcoming in the future. This talk will concentrate on the potential downsides of implementing an SBRT strategy for a high risk population in advance of Level one evidence and will suggest safe strategies for testing this interesting concept in the future .

SP-0679 T. Zilli Switzerland

Abstract not available