Irradiation Facility for Pre-Clinical Proton Therapy Studies

Proton therapy is a form of radiation therapy that has been gaining traction as a treatment method for certain difficult-to-reach cancers, as it offers many advantages with respect to conventional radiation therapy in terms of healthy tissue sparing. In this framework, pre-clinical studies are a crucial step in the development and study of new techniques to enhance the therapeutic ratio of proton therapy. The Bern Medical Cyclotron has been adapted to produce a proton beam suitable for in-vitro proton therapy studies, providing an accessible proton therapy research facility in Switzerland. 

The sparing effect of treatment delivery at ultra-high (FLASH) dose rates on healthy tissue is currently a topic of great interest in radiation therapy research, with first human clinical trials having recently been performed. The Bern Medical Cyclotron was designed for routine use at high currents for radiopharmaceutical production, making it suitable for delivering a proton beam at ultra-high dose rates for pre-clinical investigations of the FLASH effect in proton therapy.

Another technique to enhance healthy tissue sparing in radiation therapy that is currently under investigation is spatial fractionation, which makes use of an array of high- and low-dose regions in the treatment volume as opposed to a conventionally uniform radiation field. The highly modular and customizable nature of our setup allows us to collimate the extracted beam to a variety of spatially fractionated configurations for investigations of this effect. 

In-vitro studies at conventional rates have already been performed at the Bern Medical Cyclotron in collaboration with the University of Bern Institute of Anatomy, with plans for further studies at FLASH rates and using spatially fractionated beams underway.


Photo of experimental setup for proton therapy studies
Photo of experimental setup for proton therapy studies

Technical Details

The beam is passively scattered and collimated, and extracted into air at 15.4 MeV through a 55 mm diameter exit window. With this setup, a dose uniformity of 11% within the full field size can be achieved, or 6% within a diameter of 1.5 cm. Dose rates in the range of 0.03 to 100 Gy/s can be extracted with this setup and delivered to the desired target.

Real-time dosimetry at conventional rates is performed using an in-beam ionisation chamber, which has been calibrated using radiochromic films. For beam delivery at ultra-high dose rates, dosimetry is currently under investigation . 

To deliver a short pulse of protons at ultra-high dose rates, we make use of a remotely controlled chopper wheel (see picture) to deliver a controlled pulse. 

Spatial fractionation of the extracted beam with a fine-toothed collimator is also currently under investigation.


Photo of beam chopper wheel used for irradiations at FLASH dose rates
Photo of beam chopper wheel used for irradiations at FLASH dose rates