SU‐F‐J‐189: A Method to Improve the Spatial Resolution of Prompt Gamma Based Compton Imaging for Proton Range Verification

Abstract

Purpose:To test two new techniques, the distance‐of‐closest approach (DCA) and Compton line (CL) filters, developed as a means of improving the spatial resolution of Compton camera (CC) imaging.Methods:Gammas emitted from 22Na, 137Cs, and 60Co point sources were measured with a prototype 3‐stage CC. The energy deposited and position of each interaction in each stage were recorded and used to calculate a “cone‐of‐origin” for each gamma that scattered twice in the CC. A DCA filter was developed which finds the shortest distance from the gamma's cone‐of‐origin surface to the location of the gamma source. The DCA filter was applied to the data to determine the initial energy of the gamma and to remove “bad” interactions that only contribute noise to the image. Additionally, a CL filter, which removes gamma events that do not follow the theoretical predictions of the Compton scatter equation, was used to further remove “bad” interactions from the measured data. Then images were reconstructed with raw, unfiltered data, DCA filtered data, and DCA+CL filtered data and the achievable image resolution of each dataset was compared.Results:Spatial resolutions of ∼2 mm, and better than 2 mm, were achievable with the DCA and DCA+CL filtered data, respectively, compared to > 5 mm for the raw, unfiltered data.Conclusion:In many special cases in medical imaging where information about the source position may be known, such as proton radiotherapy range verification, the application of the DCA and CL filters can result in considerable improvements in the achievable spatial resolutions of Compton imaging.