First Demonstration of a Prompt Gamma Slit‐Camera for in Vivo Proton Range Verification Based On Semiconductor Detectors

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Medical Physics





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Purpose: To demonstrate the feasibility of using a solid‐state semiconductor slit‐camera in prompt gamma imaging (PGI) for proton range verification during proton therapy with pencil beam scanning mode. Methods: The PGI system based on an array of semiconductor detectors was designed using TOPAS Monte Carlo tool. An array of CZT detectors with a 6‐mm‐width knife‐edge shaped slit tungsten collimator was used to project the prompt gamma depth emission profiles produced by proton beams in a patient phantom. The detector array contains 40 individual CZT detectors arranged in two rows to score events between 3 and 6 MeV. Each detector is 20 mm thick, 100 mm high, 4 mm wide along the beam axis. The built‐in scanning nozzle worked in pencil beam scanning mode. To demonstrate the utility of the camera for range verification, the axial beam shifting in a PMMA cylinder and ranges of the distal beam spots in the central slice of C‐Shape dose delivery in the TG‐119 phantom were measured, respectively. Results: The energy spectra measured from prompt gamma emission in PMMA irradiated with 160 MeV proton beam show the 4.44 MeV peak from de‐excitation of ¹²C. The gamma emission between 4.0 and 5.0 MeV contributed to the majority of detected profiles. With the collimator at 15 cm away from the beam axis, a 1 mm standard deviation on range estimation in PMMA phantom irradiated with the pencil beams of 2.2 × 10⁸ protons at 160 MeV can be achieved. With the collimator at 25 cm away from the beam axis, a 3 mm standard deviation on range estimation in TG‐119 phantom for the distal beam spots was obtained. Conclusion: Results confirmed the feasibility of the PGI system based on a CZT semiconductor slit‐camera for range monitoring with millimeter accuracy using pencil beam scanning mode in a typical clinical setting.


Medicine and Health Sciences



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