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Description
Hadron therapy is an emerging form of cancer treatment that shows to be more effective than the most widespread type of radiotherapy treatment with X-rays, due to the nature of the energy deposition of hadrons. Before the treatment, there is a need for the imaging of the patient, which is usually done by using X-ray CT. However, with the usage of the conventional X-ray CT, a conversation of the Hounsfield units (describing the photon's absorption) to Relative Stopping Power values (describing how fast the hadrons stop in different materials) is necessary and introduces ~7% error. A possible solution for eliminating the uncertainty could be imaging with the same particle that is used for the treatment later.
This work focuses on the comparative analysis of proton, helium-ion, and carbon-ion computed tomography (CT) as direct imaging modalities for hadron therapy treatment planning, focusing on Relative Stopping Power (RSP) reconstruction accuracy and patient radiation dose. For this, high-fidelity Monte Carlo simulations were conducted using the GATE/Geant4 platform to model a standard CTP404 phantom. RSP maps were reconstructed using two iterative algorithms: the Simultaneous Algebraic Reconstruction Technique (SART) and the Richardson-Lucy (RL) deconvolution. Imaging performance was evaluated by comparing reconstructed RSP values against ground truth data for various tissue-equivalent inserts, while integral doses were estimated for a human head geometry using a Shepp-Logan-like phantom.
All investigated particle modalities demonstrated a significant dose reduction compared to conventional X-ray CT protocols (which are approximately 40 mGy). The estimated imaging doses were $0.5$ mGy for protons, $1.3$ mGy for helium ions, and $7.5$ mGy for carbon ions.
In terms of accuracy, carbon-ion imaging achieved promising accuracy for soft-tissue materials (mean absolute error $<0.5\%$). Helium ions offered a balanced performance with sub-$1\%$ errors for most materials and a dose burden significantly lower than carbon ions. Protons exhibited the widest range of RSP deviations.
Direct particle imaging eliminates the systematic uncertainties inherent in photon-to-hadron conversion, which typically introduce RSP deviations of 1.6\%–3.5\% in standard single-energy X-ray CT. While carbon ions provide better RSP reconstruction precision essential for complex treatment plans in heterogeneous anatomy, helium and proton imaging offer exceptional dose sparing, making them particularly advantageous for pediatric patients and frequent adaptive replanning scenarios.