The cancer treatment technique of proton therapy has more than 60 years history and recently arrived to Spain. It allows for a more selective treatment of tumors since higher dose is concentrated in the region where the protons stop, whereas far less dose is deposited in the surrounding tissue as compared to radiotherapy with X- or -rays. In this context, a system of imaging and dose verification to define effective and accurate treatment plans and to guarantee the correct location of the applied dose is mandatory.
Currently, the treatment planning is guided via X-ray computed tomography (X-ray CT) images. Since the energy deposition by X-rays in matter differs from that of protons, the lack of accuracy in the estimation of proton ranges calculated using X-ray images is quite large (~3 %) coming mainly from the conversion from Hounsfield units (HU) to Relative Stopping Powers (RSP). Meanwhile, treatment plans made via proton-CT images will offer more accurate estimations and better control of the treatment.
To this aim, we are building a prototype for pCT scanner using particle detectors extensively used in experimental nuclear physics. Those are the Double-Sided-Silicon-Strip-Detectors (DSSDs) and the LaBr3(Ce) scintillation detectors. The former, being segmented horizontal and vertically, are to be used as tracking detectors and the latter, an array of 2x2 modern scintillators of LaBr3(Ce) offering fast response and good energy resolution, is to be used as residual energy detector. With these detectors, we map the energy losses with respect to horizontal and vertical positions to produce a spatial image of the sample, and obtain a 3D distribution of Relative Stopping Powers (RSP) needed for proton therapy treatment plans.
In this contribution, we report on a proof-of-concept test using a simpler experimental setup with low-energy protons (10 MeV) carried out at the CMAM tandem (Madrid, Spain) in June 2019. The work of Monte Carlo simulations to optimize the setup, the data-taking and the analysis was the topic for two Master theses. Our future plans will be presented including two experiments where we plan to test our full prototype at realistic proton therapy beam energies. These experiments are already approved at KVI-CART (Groningen, Netherlands) and CCB (Krakow, Poland) and will be performed in 2021.