ESTRO 38 Abstract book

S347 ESTRO 38

1 Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy

from two large-scale randomized trials (De-ESCALate and NRG Oncology RTOG1016), both showing significantly worse tumor control and survival outcomes for patients treated with Cetuximab, with comparable frequency and severity of acute toxicity and late morbidity. In this light, Cisplatin continues to be the standard of care for radiosensitation in all eligible patients with advanced HPV positive OPC, and treatment de-intensification strategies should only be evaluated within the frames of well- designed clinical trials. The focus of this talk will be to summarize the current understanding of how to optimally treat HPV positive OPC integrating an overview of the design and rationale of ongoing clinical trials and a presentation of lessons learned from completed clinical trials. SP-0661 Predictive models in treatment of head and neck cancer H. Langendijk 1 1 UMCG University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands Abstract text The relationship between 3-dimensional dose distributions and risks on radiation-induced side effects can be described by Normal Tissue Complication Probability (NTCP) models. NTCP-models may contain only one dose- volume predictor (dose metrics), but generally the performance of these model significantly improve when adding multiple other predictors (multivariable NTCP- models). According to the so-called model-based approach, next to outcome prediction, NTCP-models can be applied for dose optimization, selecting the best radiation technology, plan adaptation and even technology validation. For many side-effects, the risk may depend on more than one dose metrics to different organs at risk (OARs). To produce treatment plans that eventually result in adequate target dose coverage with the lowest probability on side effects, dose distributions to OARs should be translated into NTCP-profiles using NTCP- models (model-based dose optimization). For the selection of the best treatment plan, or even for the selection of patients for more advanced radiation technologies, like protons, information on NTCP-profiles next to dose profiles are essential to ultimately obtain the best clinical result, i.e. local control with the lowest rates of radiation-induced side effects. Currently, adaptive radiotherapy is mainly guided by dose deviations compared to the nominal plan. However, depending on the shape of the NTCP-curve, apparently large dose deviations do not necessarily translate into clinically relevant changes in the risks of side effects. Vice versa, relatively small dose deviations may result in major changes in the risk of side effects when they appear in the dose range with the steepest dose-effect relationship. Also here, NTCP-guided adaptations, also referred to as biologically-driven adaptive radiotherapy (BIOART) is more likely to result in the best clinical result. Many radiation technologies aiming at reduction of side effects are introduced in routine clinical practice, based om the ALARA-principle without any proper clinical validation. An alternative for RCT’s is the so-called model-based validation, testing the null-hypothesis that observed toxicity rates obtained with the new RT technology is similar to that expected (based on NTCP-models) from the old technology. In summary, the model-based approach allows for a continuous improvement and validation of newly introduced radiation techniques and ultimately the most optimal outcome for patients treated with radiotherapy. SP-0662 Immunotherapy in HNC – when and for whom, biomarkers of response L.Licitra 1

Abstract not received

Symposium: New detector developments

SP-0663 Update on compact graphite calorimeter for absolute dosimetry measurements T.Russell 1 1 National Physical Laboratory,Teddington United Kingdom SP-0664 Update on commercial scintillators S. Beddar 1 1 The University of Texas MD Anderson Cancer Center, Radiation Physics, Houston- TX, USA Abstract text Within the last two decades, there has been a substantial research directed towards the use of scintillators to measure absorbed dose in radiation dosimetry in general and particularly in radiation therapy. The evolution of the many studies that focused on these new type of detectors followed 3 phases: 1) identifying suitable clinical applications where scintillation detectors would offer additional advantages over the commonly used detectors or dosimeters, 2) optimization of detector designs and component’s system depending on the application of interest and 3) transfer and translation to the industry to commercialize these new detectors. A brief introduction to scintillation dosimetry, including a summary of their advantages and disadvantages will be presented. The lecture will focus on commercial scintillators and an update on their present status including new scintillation detector developments that are ongoing. At the present time there are two commercial systems available on the market. One designed for absorbed dose and dose characterization for external beam radiation therapy (EBRT) commercialized by Standard Imaging. The second one designed for in vivo dosimetry and dose monitoring commercialized by Radiadyne. A third commercial system is in the development and clinical trial testing phase for HDR brachytherapy to be commercialized soon by Dosilab. Their first system is targeted at the QA of HDR brachytherapy equipment. Finally, current and on-going research to respond to future needs such as brachytherapy in the domain of in vivo dosimetry and dose-tracking, including electromagnetic (EM) tracking will be presented. SP-0665 Multichannel film dosimetry I. Mendez Carot 1 1 Institute of Oncology Ljubljana, Department of Radiation Physics, Ljubljana, Slovenia Abstract text The dosimetry system composed of radiochromic films and a flatbed scanner is a dosimeter of choice in many radiotherapy and radiology applications. Upon irradiation, films polymerize, becoming increasingly dark with the absorbed dose. Variations in the visible absorption spectrum can be measured with a scanner, which yields three different signals (R, G and B), one for each color channel. Multichannel film dosimetry consists of the combination of the information provided by several color channels in order to obtain more accurate dose distributions. Various multichannel film dosimetry methods have been proposed in the literature. Each of them based on different assumptions regarding the Abstract not received