Prompt Gamma-Ray Range Verification in Particle Therapy

Particle therapy (PT) has become a widely accepted and promising option for tumor treatment. It supplements conventional radiation therapy with MV X-rays and electrons and is becoming increasingly important for more and more applications. More than 100 clinical PT facilities are already in operation worldwide, around 40 are currently under construction and just as many are planned.
The accuracy of the prediction of the particle range in the tissue is, however, influenced by uncertainties in patient positioning, by patient movements during irradiation, by anatomical changes during one or between several fractions and by other factors that are difficult to quantify in daily clinical routine. These uncertainties are considered by conservative safety margins in the treatment planning, but these margins reduce the advantage of particle beams compared to conventional therapies in many cases. Real-time range verification is therefore a necessity in order to exploit the full potential of particle therapy.
Range verification of therapeutic ions has been investigated for over 50 years now. Many systems have been developed in this time, some devices have been tested under clinical conditions and only a few make it to clinical trials. However, so far there is no system that is used in daily clinical routine. While the first devices still made use of the annihilation radiation of the positron emitters generated in the therapy, the international community mainly concentrates on the use of prompt gamma rays today.
This talk gives an overview of the current status of prompt gamma-ray based range verification. The focus is on the three currently most promising options (Prompt Gamma Ray Imaging, Spectroscopy and Timing). The metrological fundamentals of the individual systems are presented and discussed with regard to their use in everyday clinical practice.