ESTRO 36 Abstract Book

S260 ESTRO 36 2017 _______________________________________________________________________________________________

The latest data from large prospective phase III hypo- fractionation studies, such as the CHHiP trail, support the notion that the α/β ratio for prostate cancer might be as low as 1.5Gy, and therefore offer the opportunity to utilise hypo-fractionation to broaden the therapeutic ratio. Additionally, highly conformal treatment plans and reduced margins due to advanced image guidance as well as the use of adaptive approaches further decrease the doses administered to the organs at risk. The broadened therapeutic ratio and the highly conformal planned and accurately administered treatment plans allow for further dose escalation to the prostate while maintaining low toxicity. However, with the rectum and the bladder being - more or less - directly adjacent to the prostate there is still a need for an approach to further reduce the dose delivered to the organs at risk. Reviewing the current literature reveals that spacers offer an invasive, but safe and effective way to partly overcome the spatial proximity by introducing additional material between the prostate and the rectum. The increased distance – which is mostly reported to be in the range of approximately 1 cm – is clearly correlated to a significant reduction of administered doses and the volumes of the rectum receiving high doses respectively; including the anterior rectal wall which can otherwise hardly be spared. Especially the clinically important volumes receiving a high percentage of the prescribed dose or an EQD 2 of more than 60 or 70 Gy, which could lead to severe acute and late side effects can be significantly reduced. Several studies clearly demonstrate these dosimetric benefits of the different materials currently available. Nevertheless, there is a certain learning curve that has to be absolved to fully exploit the potential of such spacers. Another property that all of them share is that the materials are resorbed after a certain time. While all the different materials/approaches such as hyaluronic acid, hydrogels or balloons are fundamentally based on the same principle – to create a space between the prostate and the anterior rectum wall – each has slightly different characteristic. The spacer balloon (Bioprotect TM ) for example, has been shown to result in an advantageous dose distribution compared to spacer gels; however, it also has been shown to shrink substantially during the course of a treatment, thus losing some of its initial advantage. Factors such as the detailed course of the resorption, together with the handling during injection/placement, the achievable increase of the distance, the actual shape and its stability, the possible influence on prostate movements, as well as the possible toxicity/side effects inflicted by the spacer itself are the factors that need to be considered when comparing the different materials/approaches. According to the available literature, there is no evidence yet that one material is generally superior to the others, showing only slightly different properties that need to be weighted to choose the one fitting the respective requirements. However, several of the properties still need to be further evaluated and compared offering interesting research opportunities. SP-0494 Using a MRI-guided radiation therapy system for prostate cancer patients O. Bohoudi 1 , A. Bruynzeel 1 , S. Senan 1 , B. Slotman 1 , M.A. Palacios 1 , F. Lagerwaard 1 1 VUMC, Radiotherapy, Amsterdam, The Netherlands Recently, stereotactic MR-guided adaptive radiation therapy (SMART) for prostate cancer has been clinically implemented at our center, using the MRIdian system (Viewray, Inc, Cleveland OH). This dedicated device combines a split-bore 0.35T MRI which has real-time imaging possibilities, and a radiotherapy delivery system consisting of a ring gantry with three multileaf collimator- equipped 60Co heads. An integrated Monte Carlo-based treatment planning system in combination with an

independent adaptive QA system, allows for online adaptive (re-)planning based on the actual daily anatomy for optimal dose delivery. We report on the first year of clinical experience with SMART for prostate patients. Here we describe the clinical implementation and workflow, provide details on daily plan adaptation and gated radiation delivery under real-time MRI-guidance.

Symposium: Young ESTRO meets ESTRO School

SP-0495 Introduction of FALCON (Fellowship in Anatomic delineation and CONtouring) online contouring system as a tool for e-learning J.G. Eriksen 1 1 Odense University Hospital, Department of Oncology, Odense, Denmark Heterogeneity in contouring of target volumes and organs at risk is one of the major uncertainties for modern radiotherapy planning. Competencies in delineation requires both knowledge and skills obtained under supervised practice in the clinic. Several online possibilities for training contouring exists and can be a valid supplement in training and maintaining of skills in delineation. The ESTRO teaching programs called FALCON (Fellowship in Anatomic delineation and CONtouring) – using the EduCase platform - is presented. SP-0496 Role of radiotherapy in the treatment of stage IIIA/pN2 non-small cell lung cancer L. Käsmann 1 1 University of Lübeck, Department of Radiation Oncology, Lubeck, Germany Lung cancer is the leading cause of cancer mortality, surgery and radiotherapy play key roles in curative treatment of this disease. Stage III comprises a heterogeneous group of tumours and an optimal multimodal treatment is warranted. However, the role of postoperative radiotherapy in the treatment of stage IIIA/pN2 non-small cell lung cancer (NSCLC) remains controversial. Pre-operative staging based on endoscopy and the use of FDG-PET has improved in the last decade. Radiotherapy technology is also emerging with 4D-CT simulation and cone beam CT for image-guidance resulting in improved survival. Meta-analysis of the PORT phase III studies using several radiotherapy technique (Cobalt, 2D- planned, 3D-conformal) show conflicting data. In the first part of this presentation we will outline the controversy of radiotherapy in the treatment of stage IIIA/pN2 non- small cell lung cancer according to the latest literature and international guidelines. Besides we will present an interesting case with focus on treatment planning, target definition as well as delineation guidelines using the e- learning programmes "Falcon" and "Dove" for a practical overview. SP-0497 Role of radiotherapy in the treatment of stage IIIA/pN2 non-small cell lung cancer B. Jeremic 1 1 Belgrade, Serbia, Stage III non-small cell lung cancer (NSCLC) is a heterogeneous disease presentation based on the range of patient and tumor characteristics. Concurrent radio- chemotherapy (RT-CHT) is the standard treatment approach for inoperable stage III NSCLC. However, in certain favorable subsets of patients with Stage III, namely those with low burden stage disease (i.e. IIIA/pN2), there seems to be greater potential for cure. In this setting, treatment regimens consisting of surgery alone or in combination with adjuvant CHT- and/or RT have been historically among the most common approaches used,