Room: Exhibit Hall | Forum 2
Purpose: To experimentally investigate a new concept for tumor localization during proton therapy via proton and secondary neutron interactions in gadolinium (Gd) producing a series of characteristic photons in the energy region of 40-200 keV.
Methods: Gadolinium solutions of 1 mg/g and 10 mg/g were irradiated using a 5 cm (0-5 cm) SOBP from a passively scattered proton beam from Mevion S250. Phantom irradiations were performed for a 10Ã—10 cmÂ² field size at a dose rate of 124 MU/min. Spectra were recorded using a 25 mmÂ², 1 mm thick uncollimated X-123 CdTe spectrometer placed 10 cm away from the phantom. The neutron capture characteristic photon intensity was determined for the Gd solution.
Results: Characteristic Gd X-rays (43 keV KÎ± and 49 keV KÎ²) expected from internal conversion after Gd neutron capture were observed in the measured spectrum, however there was no visible indication of the Gd prompt gamma-rays (at 79.5 keV and 181.9 keV). This discrepancy is postulated to be due to the large drop in intrinsic detection efficiency over this energy range for the CdTe detector. However, there is a possibility that the observed X-rays may be from PIXE reactions. Despite this, the SNR was found to be greater than 20 for the single element detector, and the detected count density of the characteristic X-rays was greater than 14,000 counts/cmÂ².
Conclusion: This research demonstrates the first detection of the characteristic X-rays of Gd produced by a proton therapy beam. Measurements with a higher efficiency detector will allow us to determine the reaction source contributing to Gd detection. Forthcoming work is to be focused on simulating this work in GATE/Geant4 and to produce a reconstructed image of Gd signal to determine the feasibility of an online nuclear medicine detection system to measure the tumor location via gadolinium based contrast media.
Funding Support, Disclosures, and Conflict of Interest: Funding supported by The Natural Sciences and Engineering Research Council of Canada (NSERC)
Not Applicable / None Entered.