Proton therapy is a cancer treatment technique that allows for a more selective application of dose to tumors in comparison with conventional radiotherapy with X- or $\gamma$-rays. This is due to the fact that higher dose is concentrated in the region where the protons stop, whereas far less dose is deposited in the traversed tissue. 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.
However, the treatment planning in proton therapy facilities is guided via X-ray computed tomography (X-ray CT) images. This requires the conversion “a posteriori” of the map of Hounsfield Units (HU) obtained from X-ray CT to Relative Stopping Powers (RSP) useful for proton therapy treatment plans . This conversion induces a large uncertainty in the range of the protons (up to 5% in the abdomen and up to 11% in the head) [2-4]. Meanwhile, treatment plans made via proton-CT (pCT) images will offer more accurate estimations of proton ranges with an uncertainty below 1% and a better control of the treatment .
With this purpose, 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 LaBr$_3$(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 LaBr$_3$(Ce) offering fast response and good energy resolution, is to be used as residual energy detector. With these detectors, an image of the sample is taken by mapping the energy losses with respect to horizontal and vertical positions. In this way, we obtain a 3D distribution of Relative Stopping Powers (RSP) needed to design proton therapy treatment plans.
A first test using low-energy protons (10 MeV) was carried out at the CMAM tandem (Madrid, Spain) in June 2019 to test the proton tracker. Monte Carlo simulations were used to optimise the setup and obtain predicted images of the scanned 2D objects. A second experiment at proton energies relevant in proton therapy (100-200 MeV) will be performed in Cyclotron Centre Bronowice (CCB) in Krakow (Poland) in May 2021. This second measurement will allow to test and optimise the full setup, including the residual energy detector by scanning 3D objects.
In this contribution we report on the results of the first test at CMAM (Madrid) which demonstrated the viability of the pCT scanner prototype. Additionally, preliminary results from the study at CCB Krakow will be shown.
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