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Brachytherapy source tracking with in vivo dosimetry and some important benefits of inorganic scintillation detectors

Kolloquium der Abteilung 6

In vivo dosimetry (IVD) is one of the most direct ways to ensure that the correct dose is delivered to the patient. Still, IVD is not standard practice in brachytherapy (BT) today. One important reason is the steep dose gradient in BT, which requires a very accurate positioning of the dosimeter. For instance, a small few millimeters-offset of the dosimeter or of a nearby (<3cm) needle can lead to dose deviations >20%, without having any impact on the quality of the treatment. However, larger shifts of needles far away from the dosimeter, but in critical positions for the patient, can go unnoticed if the resulting small dose deviations at the dosimeter position are not detectable. Commercially available IVD systems for BT only report the total dose post-treatment, which limits the possibility to react on treatment errors. As a consequence, BT clinics are not using IVD and in principle are delivering the dose blindfolded. New developments within flat panels as well as point detectors for IVD in BT have opened up for a paradigm shift. The new dosimeter systems can provide dose rate measurements with high precision and in real-time. The systems can also provide information at a sub-second level, which allows for both real-time treatment verification and dose rate information for individual dwell positions. The steep dose gradient in BT makes it possible to determine the relative distance between the source and dosimeter with a high accuracy based on the dose rate information. This enables tracking of the source with triangulation-based algorithms that use the measured dose rates to determine the position of the source relative to the dosimeter.
Recent developments within IVD and a real-time detector system based on inorganic scintillators will be presented together with a discussion of the pros and cons of source tracking with IVD.