Secondary prompt gamma-rays to improve proton range verification

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Saunders, Jessica
Erickson, Anna S.
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The goal of this research is to evaluate the secondary prompt gamma (PG) yield from proton therapy at high characteristic energies from MC model simulations and experimental data. Recent studies indicate that target composition influences PG characteristic energy and yield, and the quantification of PG may be used to offer real-time dose verification for proton therapy. In this study PG analysis was performed for MC simulations to evaluate the characteristic measurements and total yield of secondary PG emitted from a target in the 0-8 MeV range from a proton therapy beam over a range of four different beam energies (70 MeV, 160 MeV, 200 MeV, 220 MeV). This was repeated in several target materials (carbon, calcium oxide, calcium fluoride, PMMA, and HDPE) in order to evaluate the influence of the incident energy and the target material on the PG yield and energy spectra. PG energy spectra determined from the specified target materials indicated that the 3.74 MeV energy peak shows a linear correlation between PG intensity and calcium mass fraction of the target material. 6.13 MeV and 4.44 MeV energy peak are not unique to the respective, oxygen and combined oxygen and carbon, mass fraction of the target material. This relationship is complicated by the addition of calcium within the target. Experimental data was collected in order to validate the computational model based on comparison of relative characteristic energy peek intensities. The relative peak ratio determined from experimental data is in good agreement with model prediction, the combined peak ratio is within 0.2%.
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