ESTRO 37 Abstract book

S337

ESTRO 37

dosimetry of small fields and also introduced two new types of reference fields: (i) a static machine-specific reference (msr) field for those modalities that cannot establish conventional reference conditions and (ii) a plan-class specific reference (pcsr) field closer to the complex patient-specific clinical fields thereby facilitating standardization of composite field dosimetry. The first Code of Practice for the dosimetry of small fields in photon beams has been published by members of the same working group as IAEA TRS-483 [4], which contains six chapters providing an introduction, a brief discussion of the physics of small photon fields, the formalism, a comprehensive overview of suitable dosimeters, practical recommendations for msr dosimetry and practical recommendations for the determination of field output factors in small-field photon beams. Two appendices provide comprehensive compilations of data and their uncertainties from the literature that form the basis of the data used in the Code of Practice. Current efforts include an IAEA Coordinated Research Activity to test IAEA TRS-483 in the clinical environment [5] of which a status will be presented and an update of IAEA TRS-398 which will include, similarly as the Addendum to AAPM TG-51, Monte Carlo calculated overall beam quality correction factors [6]. The IAEA also intends to review the status of pcsr dosimetry and explore the possibility of developing recommendations for composite- field reference dosimetry [6]. [1] M. McEwen et al. Addendum to the AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon beams. Med. Phys., 41:041501, 2014. [2] M. M. Aspradakis et al. Small field MV photon dosimetry. IPEM Report 103. Institute of Physics and Engineering in Medicine, York, UK, 2010. [3] R. Alfonso et al. A new formalism for reference dosimetry of small and nonstandard fields. Med. Phys., 35:5179–5186, 2008. [4] H. Palmans et al. Dosimetry of Small Static Fields used in External Beam Radiotherapy: An IAEA-AAPM international Code of Practice for reference and relative dose determination. Technical Report Series No. 483. International Atomic Energy Agency, Vienna, 2017. [5] W. Lechner et al. Initial experiences in Testing the IAEA/AAPM Code of Practice on Small Field Dosimetry. International Conference on Advances in Radiation Oncology (ICARO-2), Vienna, Austria, 20–23 June 2017 [6] K. Christaki. Personal communication, 2018. SP-0641 Treatment planning: where are we and, where are we going O. Bohoudi 1 1 VUMC, Radiotherapy, Amsterdam, The Netherlands Abstract text Radiation therapy treatment planning has undergone major revolutions in the past decades. Innovations in the field of computerized planning technology and the introduction of advanced radiation delivery equipment have resulted in decreased usage of 2D and 3DCRT techniques, in favor of techniques such as IMRT, VMAT and tomotherapy. In addition, current developments such as MR-guided radiation therapy allow for adapted treatment planning, whereas the introduction of stereotactic treatment delivery and proton beam therapy pose their own specific challenges. This has (had) an enormous impact upon treatment planning itself and on the requirements of physicists and/or RTT. Novel planning aspects that are evaluated in current practice are model-based planning and scripting. This Teaching Lecture: Treatment planning: where are we and, where are we going

presentation provides an overview of some of the above developments in treatment planning, and more specifically, the following topics will be discussed: – An overview of current treatment planning applications. – Treatment planning and machine learning. – The changing role of planners. – Aspects such as robust and adaptive planning, model- based planning will be illustrated for radiosurgery for multiple brain metastases and adaptive planning for MR- guided radiation therapy.

Joint Symposium: ESTRO-EORTC: New strategies for a clinical research partnership?

SP-0642 OLIGOCARE, the EORTC ESTRO initiative for oligometastasis: a pragmatic platform P. Ost 1 1 University Hospital Ghent, Radiation Oncology, Gent, Belgium Abstract text Despite its almost universal use, the level of evidence supporting radical local treatment for oligometastases in general, and stereotactic radiotherapy in particular, is low. Furthermore, oncology has evolved and changed rapidly within the last years due to more effective systemic treatment (e.g. targeted drugs, immunotherapy), better imaging and diagnostics for disease staging and characterization (e.g. PET scanning, circulating tumor DNA) and more frequent use of multimodality treatment. These factors all potentially influence the effectiveness of local treatment in the oligometastatic setting. Consequently, there is an urgent need for better patient selection criteria for or against local treatment in general and SRT in particular in the setting of oligo-metastasis.However, it is considered as highly unlikely or even impossible that these questions will be answered within the traditional framework of prospective randomized trials, randomizing patients between systemic treatment only or addition of a local treatment component. This is mostly because of two reasons: 1. There are no major technical challenges to safely treat oligometastases in routine practice despite the lack of mature randomized data. Consequently, the equipoise to enroll patients in trials randomizing between SOC and SOC plus SRT is low in many countries, except for some countries like the UK, where the use of SRT is more strictly regulated. 2) The situation of oligo-metastases is complex and diverse in terms of primary cancer type, time of oligo- metastases development, previous treatment of the loco- regional primary cancer, imaging used for staging of oligo-metastases, number, location and size of oligometastases, integration of local treatment into a systemic treatment strategy, choice of radical local treatment approach and clinical endpoint. Systematically addressing all these questions through traditional prospective clinical trials is not possible. Consequently, there is a strong clinical and scientific need to pursue alternative strategies to advance the field of oligometastases. Traditional prospective interventional trials are required for answering answer proof-of- principle questions. On the other side, the broad clinical implementation and practice of stereotactic radiotherapy for oligometastases within the European community offers the opportunity to establish a large European prospective registry trial. The diversity inherent to oligometastases treatment techniques requires a European approach to ensure the collection of data from a sufficiently large patient cohort in order to answer the questions listed below. This type of pragmatic trial, also