ESTRO 37 Abstract book

S62

ESTRO 37

SP-0126 Quality assurance in daily clinical practice F.A. Siebert 1 1 University Hospital S-H Campus Kiel, Academic Physics, Kiel, Germany Abstract text Brachytherapy (BT) is a well-established form of radiotherapy that results in very good patient-outcome with low toxicities as it was proofed in many publications, e.g. for breast, gynecological, and prostate cancer. To ensure a high quality of treatment and minimizing the risks, a well-structured quality assurance (QA) is necessary. To promote and develop such QA procedures the GEC ESTRO working group BRAPHYQS was established and published papers and guidelines on QA in BT. Several implants in BT are based on cross-sectional ultrasound (US) imaging. BRAPHYQS elaborates European guidelines for QA of ultrasound imaging in brachytherapy containing many practical procedures and hints. These guidelines explain tests for image quality as well as geometrical checks like for volume and scaling measurements. In addition template calibration is depicted and a chapter explains QA for stepping devices and US-based applicator reconstruction. Another important topic in BT is source calibration. In particular source calibration for low-energy photon emitting sources is complex. The calibration standards of European Standard Laboratories are presented. Furthermore the necessity for the medical physicists in the clinics for LDR source calibration is highlighted. What uncertainties can be accepted in variation of air-kerma- strength after the delivery of the seeds in the clinics, and how should air-kerma strength be measured? The treatment planning systems (TPS) used in BT must be commissioned and periodically checked. For this important task no practical European guidelines exist. Thus, BRAPHYQS started a project on TPS commissioning and periodically testing. In the resulting report not only TG 43-formalism based dose computation are covered but also data import/export, imaging, contouring, dose- volume-histograms, and applicator libraries. For advanced calculation methods the model-based-dose calculation working group of AAPM/ESTRO/ABG already published some guidelines, and at the IROC at MD Anderson test data sets can be downloaded for benchmarking purposes. SP-0127 Multi-parametric functional imaging for tumour classification W. Van Elmpt 1 , A. Even 1 1 MAASTRO Clinic, Department of Radiation Oncology, Maastricht, The Netherlands Abstract text Multi-parametric imaging has the potential to characterize biological and functional properties of tumours. Imaging is used to quantify processes such as hypoxia, vascularization or metabolic activity. In this presentation a focus on multi-parametric imaging techniques for tumour classification of lung cancer patients is given. Multi-parametric image analysis techniques are currently developed for visualizing the concordance of biological properties at various levels, and to stratify patients based on the corresponding tumour phenotype [e.g. supervoxel concept: See Figure 1 from Even et al; R&O 2017]. Differences between patients and cohorts of patients are quantified, but also Symposium: Multi-parametric functional imaging for patient classification, RT personalisation and response monitoring

is weighed against the reported incidence of error, radiotherapy may be seen as a safe form of treatment for cancer 1 . However, when an error does occur the consequence can be significant for the patient. Effective reporting and learning systems are a key component of a strong patient safety culture and can mitigate brachytherapy errors and near miss events. The UK has an established voluntary and mandatory reporting and learning system in place to capture brachytherapy events. Mechanisms for collating, analysing and disseminating learning from these events will be shared. An analysis of all brachytherapy events collated since 2010 will be presented. This will include a breakdown of approximately 250 events by severity, where on the pathway the error has occurred, causative factor and reported failed and effective safety barriers. Key themes and findings will be shared. SP-0125 In vivo dosimetry in brachytherapy: state of the art, available equipment and implementation in clinical routine J. Johansen 1 1 Aarhus University Hospital, Department of oncology, Aarhus C, Denmark Abstract text In most clinics in vivo dosimetry (IVD) is currently not a routine part of brachytherapy treatment verification. The main reason is the lack of appropriate equipment and methods with sufficiently high accuracy. Several attempts to use IVD have been carried out over the years with limited success. One reason is the steep dose gradients, which requires a very accurate positioning of the dosimeter, since only a few millimetres offset can lead to significant offsets in the dose. The clinics using clinically available IVD systems have therefore reported dose deviations above 20% in correctly performed treatments. Secondly, all commercially available IVD systems are based on reading out the total dose post- treatment. The lack of real-time information and the fact that only gross errors can be detected have limited the utilisation of IVD in brachytherapy. Within the last decade the development of IVD equipment has taken a leap forward, at least in the laboratories. Today, systems exists which can provide dose rate measurements with high precision and in real- time. The systems can provide information at a sub- second level, which allows both for real-time treatment verification and to gain dose rate information on the individual dwell positions in HDR. The last has led to a paradigm shift, where IVD is used to extract physically relevant parameters, like accurate dwell positions and DVHs, rather than just a point dose. The latest developments within IVD will be presented together with a discussion of the benefit in extracting dwell positions from the dose rate measurements.