Room: Karl Dean Ballroom B1
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 Â¹Â²C. The gamma emission between 4.0 to 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 2.2Ã—10â?¸ 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.