SiFi-CC for On-line Range Monitoring in Proton Therapy© Jonas Kasper
Proton and heavy ion therapy are established techniques for cancer treatment based on well-known electromagnetic interaction of ions with matter. Such a treatment is planned for each patient on a PC, validated on phantoms and afterwards the patient is irradiated. However, unlike phantoms, the human body undergoes inter- and intrafractional changes, leading to modifications of the proton beam range in a patient. This leads to a necessity of application of relatively large safety margins to over a centimeter for deeper located neoplasms.
The development of on-line monitoring tools would allow to reduce safety margins currently applied in proton therapy and optimize dose conformality in treatment planning, leading consequently to better and safer treatment.
The most promising approaches for on-line monitoring modalities are prompt gamma-based methods. Prompt gammas are produced in nuclear reactions of the particle beam within the patient.
Therefore, in a collaboration with the Jagiellonian University in Krakow and the University of Lübeck, we are developing a Compton Camera based on SiPMs and scintillating fibers. A Compton camera provides a three-dimensional distribution of the deposited dose within the patient.
The SiFi-CC is built of heavy, scintillating crystals shaped into thin fibers and then glued together to two solid blocks. The blocks are the scatterer and the absorber plane of the Compton Camera. If the incoming photons interact first via Compton effect in the scatterer and then are absorbed in a second reaction in the absorber it is possible to confine the direction of the initial photon to a cone surface. By overlaying many of these cones we can reconstruct the distribution of the energy deposition.
During the development of the SiFi-CC we take advantage of new developments in detector physics. The use of heavy scintillating fibers ensures high detection efficiency as well as excellent time resolution enabling tight electronic collimation and thus excellent background suppression. High detector granularity in combination with fast signals results in high rate capability of the system.
At the moment we conduct work on the optimization of the different setups for the SiFi-CC. For this purpose we simulate the different approaches in Geant4 and develop an analysis and evaluation framework based on the simulation. Furthermore we build a first prototype of the detector.