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Prompt Gamma Spectroscopy of Metallic Implants in Proton Therapy: A Monte Carlo Study

C Liu1*, (1) Chang Gung University, Taoyuan City, TAO, TW


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

The purpose of the study is to explore the correlation between the intensity of several spectral lines and the placement of Metallic Implants at different depths of the proton beam.

In the work, GATE/GEANT4 was employed for metallic implants phantom simulation irradiated by proton beams. Metallic Implants (including Titanium, Gold or Silver) at different depth (R50p, R80p, R90p, R100, R90d, R80d, R50d) inside the PMMA phantom is irradiated with the 150 MeV proton beam. For each simulation, 2x107 particles is achieved. Two spectra measured by an HPGE detector and an ideal detector (perfect absorber) is obtained. For each spectrum, the background is removed using the statistics-sensitive non-linear iterative peak-clipping (SNIP) algorithm.

The specific gamma lines pertaining to the metallic implants were identified. The most intense spectral lines for Titanium, Gold or Silver were at 159 keV, 1405 keV, and 633 keV, respectively. Among the materials, Silver has the largest intensity of the energy lines, followed by Gold and Titanium. The intensity of the spectral line at 633keV from Silver decreased with the increase of the depth when metallic implants were placed behind R80p. The intensity ratios (based on R80p) decrease to 67.3% at R90p, 27.2% at R100, 11.7% at R90d, 6.6% at R80d and 1.9% at R50d.

Our results indicate that the intensity of the gamma lines pertaining to the metallic implants is correlated with the placement of Metallic Implants at the depths of the proton beam. This correlation had the potential to help estimate the residual range for range verification.

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TH- External Beam- Particle/high LET therapy: Range verification (in vivo/phantom): prompt gamma/PET

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