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In vivo dosimetry in brachytherapy

Kolloquium der Abteilung 6

Treatment verification is of specific importance in brachytherapy due to hypofractionation and steep dose gradients. Furthermore, the brachytherapy workflow includes many manual processes, which increases the risk of radiation events, as most misadministrations and near misses are related to human errors. As likelihood and consequences of errors are considered more prominent in brachytherapy than in External Beam Radiation Therapy (EBRT), it is a paradox that treatment verification technologies are less developed in brachytherapy. Preliminary results from surveys within the Groupe Européen de Curiethérapie and the European SocieTy for Radiotherapy & Oncology (GEC-ESTRO) activities indicate that less than 10% of clinics perform in vivo dosimetry, while the majority of clinics are interested, if a relevant system had been available. Novel detector technology is currently opening the field of real-time in vivo dosimetry, which can improve the capacity of error detection significantly. Innovations in in vivo dosimetry are currently driven by application of real-time source tracking during treatment delivery through dose rate measurements combined with error detection algorithms. Real-time in vivo dosimetry requires dose rate detectors and currently two promising concepts are being explored: 1) small point detectors in close proximity to the source and 2) Electronic Portal Imaging Detector (EPID) panels. Many types of point detectors are available, but the interest in scintillating crystals is growing with the request for small detectors. A number of detector materials are being explored and key characteristics such as repeatability, sensitivity, energy dependence, and stability over time are being mapped out in the search of detectors which can make in vivo dosimetry most sensitive to errors and which can function optimally in the clinical workflow.