Use of a LYSO‐based Compton camera for prompt gamma range verification in proton therapy

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Abstract
Purpose: A Compton camera (CC), which measures prompt gammas (PGs) emitted during proton therapy, is a potentially useful imaging device for proton range verification. The aim of this study was to evaluate how well the reconstructed PG images obtained from various two‐stage CC configurations reproduce the distal falloff of the PG emission.Methods: We conducted Monte Carlo simulations to evaluate different two‐stage CCs positioned orthogonal to a proton pencil beam irradiating a water phantom. The results were compared with those obtained for a three‐stage CC. In particular, all detectors were made of lutetium–yttrium orthosilicate (LYSO) crystals.Results: We found that: (a) the position resolution of the detector led to more uncertainty in predicting the depth of maximum emission and distal falloff positions than did the energy resolution of the detector; (b) reducing the thickness of the absorber detector reduces the effect of position resolution on the quality of reconstructed images and improves falloff position estimates; (c) incomplete absorption of PGs can be filtered by restricting incident gamma energies to known PG energy spectral peaks; and (d) there is greater bias and less accuracy in predicting distal falloff positions with the three‐stage CC compared with the two‐stage CC.Conclusions: This study demonstrates the feasibility of using various CC designs and event selection methods to improve the imaging of PG rays. In our designed two‐stage CCs, the thin LYSO‐based absorber can provide better predictions of the distal falloff positions than the thick one. Compared to three‐stage CCs, two‐stage CCs are less biased and provide more accurate range verification.
Funding Information
  • Ministry of Science and Technology, Taiwan (MOST 105‐2221‐E‐182‐001, 106‐2221‐E‐182‐024, 106‐2221‐E‐182‐016‐MY2)

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