ESTRO 2020 Abstract book

S453 ESTRO 2020

E. Malinen 1 1 Oslo University Hospital / University of Oslo, Department of Medical Physics, Oslo, Norway

Abstract text Spatial fractionation is the delivery of radiotherapy beams through a systematic 2D grid pattern, giving a highly heterogeneous dose profile with valleys and peaks. Other names referring to the technique are among others “lattice radiotherapy” and “minibeam therapy”. The spatial periodicity of such grid patterns varies between studies, but is typically in the order of millimeters down micrometers. Spatially fractionated radiotherapy with X- rays was first used as early as 1909, and was seen to give less skin reactions compared to conventional broad beam treatment. One current motivation for the use of spatial fractionation is to induce significant tumor shrinkage without any normal tissue toxicity. The technique, typically delivered in a single fraction with high (> 10 Gy) peak dose, has been used for palliative treatment of large bulky tumors and has in some patients led to elimination of the whole tumor. The treatment has been used both as a monotherapy and neoadjuvant to conventionally fractionated radiotherapy. Similar experience has been gained in preclinical models systems. Since the treatment implies that not all tumor cells are directly irradiated, the observed control rates may potentially be attributed to local bystander effects mediated via gap-junction communication or through secretion of soluble factors such as cytokines and reactive oxygen/nitrogen species. Moreover, the immune system may also play a role as spatial fractionation results in both sparing of immune cells and the release of damage associated molecular patterns from directly irradiated tumor cells. This can trigger an immune response, affecting the whole tumor. An account of the historical development of spatially fractionated radiotherapy will be given alongside different technical solutions. Clinical and experimental findings from the literature will be presented, both in terms of tumor and normal tissue effects. The potential of using spatial fractionation to stimulate an immune response will be discussed alongside the possibility of using different radiations. SP-0723 Noninvasive cardiac radioablation for ventricular tachycardia C. Robinson 1 1 Washington University, Radiation Oncology, St. Louis, USA Abstract text Cardiovascular disease remains the primary cause of death around the world. Many patients will ultimately succumb directly or indirectly from development of arrhythmias such as ventricular tachycardia (VT) or ventricular fibrillation (VF). Current best practices for management of VT include (1) placement of implantable defibrillator, (2) medical management, and (3) invasive catheter ablation. Invasive catheter ablation (CA) has a high (50%) risk of recurrence, and significant complications which increase with repeat CA and medical comorbidities. Coupling noninvasive mapping of VT with noninvasive ablation using stereotactic ablative radiotherapy (SABR) has enabled a new treatment paradigm in the form of noninvasive Teaching Lecture: Noninvasive cardiac radioablation for ventricular tachycardia

Conclusion We presented the first nomogram modeling focusing on only centrally located NSCLC treated with SBRT. This resulted in a nomogram predicting model which is representative in our external cohort and therefore justifies the use of this nomogram within daily practice. Tuesday 7 April 2020 Day 4

Teaching Lecture: Spatially fractionated GRID radiotherapy - rationale and promise

SP-0722 Spatially fractionated GRID radiotherapy - rationale and promise