ESTRO 37 Abstract book

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ESTRO 37

introduced by the International Lymphoma Radiation Oncology Group (ILROG). The new ISRT approach allows clinical judgement based on the quality of imaging and response to modify the field based on INRT principles. It results in a significant reduction in the volume included in the previously used IFRT and markedly limits the amount of normal tissue being irradiated. A radiation technique of discharging radiation only during a monitored deep inspiration phase called DIBH (deep inspiration breath hold) has recently been introduced to the treatment of patients with mediastinal involvement. DIBH markedly reduces the exposure of heart and lungs by better separating them from the treated mediastinal nodes and reducing motion uncertainties. In early stages, favorable and unfavorable, combined modality using ISRT of only 20 or 30 Gy provides the best disease control and in comparison to chemotherapy alone, allows less chemotherapy, reduces the need for intensive and toxic salvage and even improves overall survival. The argument of radiation toxicity has become mostly irrelevant, but is still overplayed by some oncologists. Even in advanced- stage HL, there is a selective role for RT and unfortunately, RT forced retirement was not based on sound data and will be discussed. Newly approved systemic agents have not fulfilled the initial expectations and are associated with serious financial toxicity. Yet, possible synergism of RT with immune check point inhibitors is currently being explored in new programs of HL and other lymphomas and may expand the role of RT in lymphoma beyond salvage and classical limited stage indications. SP-0209 Should proton therapy clinical practice move away from a constant RBE of 1.1? H. Paganetti 1 1 Massachusetts General Hospital Harvard Medical school, Departlment of Radiation Oncology, Boston, USA Abstract text The proton RBE varies among cell lines, tissues, endpoints, as well as with beam-quality. Experimental data do show a trend towards an increase in RBE as α/β of the linear-quadratic model decreases. Furthermore, one would also expect the RBE to increase as dose decreases. The RBE also increases with increasing linear energy transfer (LET). Yet, due to experimental uncertainties and because of the fact that the majority of data is obtained in vitro, there has been no clinical implementation of a variable RBE in treatment planning. Thus, proton therapy uses a generic RBE of 1.1. Phenomenological models are capable of predicting the RBE as a function of the parameters mentioned above. Uncertainties, especially in vivo, are preventing the clinical application. Input parameters for these models are solely based on cell survival data obtained in vitro. It is unclear if in vitro relationships can be translated to in vivo endpoints even for tumor control. Furthermore, to define normal tissue complications, the endpoint of cell survival may not be appropriate at all. Most importantly, patient specific radiosensitivity is poorly understood and clinical evidence that RBE variations indeed matter in patients is scarce. RBE variations are currently not considered quantitatively in proton therapy. However, some qualitative ESTRO 37 Sunday 22 April 2018 Teaching Lecture: Should proton therapy clinical practice move away from a constant RBE of 1.1?

consideration is given towards variable RBE values by, for instance, avoiding specific beam angles or reducing the dose to critical structure for a limited number of fractions. Thus, the current clinical focus is on mitigating potential impacts of proton RBE uncertainties. This presentation will summarize our current knowledge of RBE variations as a function of normal tissue and tumor endpoints, as a function of dose, and as a function of energy deposition characteristics. Uncertainties with respect to in vivo RBE predictions will be discussed and implications in treatment planning for passive scattering and proton beam scanning will be outlined. Further, the current clinical evidence supporting a change in current clinical practice will be reviewed. Moving forward, one potential strategy is to focus on the well-known fact that the RBE is increasing with increasing LET. One can improve a treatment plan by redistributing the LET away from critical structures without significantly changing the dose distribution. SP-0210 Pre-clinical cancer models R.F. Jackstadt 1 1 Beatson Cancer Centre, Colorectal Cancer and Wnt Signalling, By Biggar, United Kingdom Abstract text Pre-clinical cancer models are a crucial tool to understand cancer biology and to find treatment strategies that will show maximized efficiency in early clinical phases. Particularly, with recent research identifying the importance of the tumour microenvironment and the potential for immunotherapy in cancer treatment, autochthonous immunocompetent models will depict an important part of pre-clinical studies in the future. Nevertheless, these models are time and cost intensive, underlining the need of models which faithfully resemble the human disease. The current state of mouse models used in pre-clinical cancer drug testing such as patient derived xenografts (PDXs) and genetically engineered mouse models (GEMMs) will be discussed, as well as assets and drawbacks of these models. Particularly, aspects of pre-clinical mouse models which lead to sub-optimal translation of therapies into the clinics will be addressed. As an example, of improved pre-clinical strategy, the stratification of colorectal cancer GEMMs primary tumours by comprehensive transcriptional profiling and cross comparison to human datasets will be highlighted. Furthermore, it will be discussed how this stratification helps to find effective tailored therapies in newly developed models which more accurately resemble the human disease. Teaching Lecture: Pre-clinical cancer models

Teaching Lecture: Supportive care in head and neck radiotherapy

SP-0211 Supportive care in head and neck cancer patients: self-management and eHealth I. Verdonck-de Leeuw 1 1 VU University Medical Center, Otolaryngology / Head and Neck Surgery, Amsterdam, The Netherlands Abstract text A major challenge in treating head and neck cancer is to obtain a high cure rate while preserving vital structures and function, preventing treatment related-symptoms, and maintaining good health related quality of life (HRQOL). The main aim of supportive care is to improve