Room: Room 202
Purpose: Uncertainty in proton range can be eliminated by proton computed tomography (CT). A new design of proton CT with a single flat detector is proposed to simplify the imaging acquisition and reconstruction.
Methods: Two strip ionization chamber plates was placed proximally to proton source on a multi-layer ionization chamber (MLIC). The strip plates measured spot locations for beam direction after beam exiting imaging object, while the integral of depth dose measured in the MLIC was translated into residual energy of the beam. Our simulation study demonstrated the feasibility and expected performance of our design. Proton stopping power ratio (SPR) was reconstructed through inverse radon transform of sinograms at intervals of one degree from 0 to 180 degrees, generated with a proton beamlet scanning through an imaging phantom. The energy of the proton beamlet was 150MeV and the spot size was 4 mm. The imaging phantom was 10 cm in diameter, made of water-equivalent material holding 13 tissue-equivalent inserts following tissue composition in ICRP 1975. All inserts were 1cm in diameter with materials ranging from inhaled lung to cortical bone. Percentage discrepancies were reported by comparing to the literature. The imaging dose, defined on total energy absorbed in the imaging phantom divided by the weight, was also reported.
Results: The SPR calculated from the proton CT showed discrepancies less than 1% in all the inserts except cortical bone which had a maximum discrepancy of 2.4%. The mean percentage discrepancy was 0.06%. The spatial resolution was 4 lp/cm and the imaging dose to the imaging phantom was 0.1 mGy.
Conclusion: Proton CT with a flat detector simplifies the data acquisition with sufficient spatial resolution and lower imaging dose compared to CBCT, making it potentially a great tool for adaptive proton therapy. Accuracy could be further improved with scatter correction.
Not Applicable / None Entered.