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Three-Stage Compton Camera Image Resolution Losses Due Detector Effects

D Mackin

D Mackin1*, J Polf2, S Peterson3, S Beddar1, (1) MD Anderson Cancer Center, Houston, TX, (2) Oklahoma State University, Stillwater, OK, (3) University of Cape Town, Capetown, ZA, South Africa

MO-G-BRA-6 Monday 5:15:00 PM - 6:00:00 PM Room: Ballroom A

Purpose: Three-stage Compton camera (CC) imaging systems may provide an effective means of detecting and imaging the prompt gamma (PG) radiation emitted from tissue during proton therapy. For these systems to be clinically viable, the resolution of the CC images should be better than the treatment planning margins, ~3 mm. Detector inaccuracies in the measured gamma interaction positions and energy depositions and Doppler broadening limit the image resolution. The purpose of our study was to determine the inherent limitations of the image resolution due to these detector effects

Methods: Using the Geant4 Monte Carlo software program, a three-stage CC detecting radiation from both gamma point sources and prompt gamma radiation emitted during proton therapy was simulated. To simulate the effects of the detector energy and spatial resolutions an independent, identically distributed random uncertainty term was applied to the MC calculated energy depositions and interaction positions. Doppler broadening was modeled using Geant4. The effects were then measured using the distance of closest approach and the point of closest approach.

Results: The major effect of Doppler broadening was to increase the size of the tails of the spatial distributions. Its effect on the full width at half maximum of the point spread function was less than 2 mm. The lateral and energy resolutions of the detector stages moderately enhanced the effects of Doppler broadening, but for the tested values of detector depth resolution, no additional effect was evident. The detector effects changed the depth of the distal falloff for PG emitted during proton therapy by < 1 mm.

Conclusions: The spatial and energy resolutions of three-stage CCs are sufficient for PG imaging during proton therapy. However, because the detector effects render many of the detected gammas unusable for reconstruction, the overall efficiency of the CC is reduced.

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