A novel portal imaging device for advanced radiation therapy

At Karolinska Institutet in Stockholm, Sweden a new detector for portal imaging is under development, which could greatly improve the alignment of the radiation beam with respect to the tumor during radiation treatment. The detector is based on gaseous and solid converters combined with GEMs as an amplification structures. The detector will have a large area and will be operated in a very high rate environment. A prototype has been built and extensively tested, both with high rate X-rays as well as in a clinical environment at the Karolinska Hospital. High rates and alpha particles could cause discharges in the GEM and discharge propagation from GEM to GEM and to the readout electronics. Since reliability is one of the main requirements for the portal imaging device, the authors performed systematic studies to find a safe operating range of the device, free from typical high-rate problems, such as discharges