Program Information
Proton Neutron Gamma-X Detection (PNGXD)
J Grafe1*, (1) Ryerson University, Toronto, ON
Presentations
SU-I-GPD-J-117 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: A new concept for tumor localization during proton therapy through activation of a contrast agent has recently been proposed, called Proton Neutron Gamma-X Detection (PNGXD). This method utilizes the ubiquitous secondary neutrons produced during proton therapy to activate a gadolinium (Gd) containing tumor contrast agent. The tertiary photons have energies of 43 keV, 79.5 keV, and 181.9 keV and are well matched for conventional nuclear medicine imaging detectors. In this study the SNR for a single pixel CdTe detector and a HPGe detector was simulated for varying tumor sizes to determine the minimum detectable tumor size.
Methods: The MCNP6 code was used to simulate the prompt gamma ray and X-ray detector signal in a 5×5×5 mm³ CdTe detector and a 5.2×5.2×4 cm³ HPGe detector for tumors ranging from 1 cm³ to 125 cm³. In all cases the proton SOBP covered the tumor, and the secondary neutron capture reactions with Gd within the tumor were tallied, along with the number of Gd photons detected. The minimum detectable tumor size was determined by setting the required prompt gamma ray signal to be 1000 counts above background (ie. a relative statistical uncertainty of 3%).
Results: The minimum detectable tumor size was 125 cm³ for CdTe and 8 cm³ for HPGe for 300 μg/g Gd tumor concentration and a 10 Gy hypo-fractionated proton dose. The minimum detectable size could decrease if the tumor Gd concentration can be increased.
Conclusion: This work demonstrates for the first time that Gd neutron capture during proton therapy occurs at a sufficient rate to be detectable by conventional spectroscopic detectors. Future experimental work is required to validate the simulations and determine if detection of prompt gamma rays produced in the tumor could produce reliable nuclear medicine images for real-time feedback of the tumor position during proton therapy.
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