Abstract
This study investigates the photon production from thermal neutron capture in a gadolinium (Gd) infused tumor as a result of secondary neutrons from particle therapy. Gadolinium contrast agents used in MRI are distributed within the tumor volume and can act as neutron capture agents. As a result of particle therapy, secondary neutrons are produced and absorbed by Gd in the tumor providing potential enhanced localized dose in addition to a signature photon spectrum that can be used to produce an image of the Gd enriched tumor. To investigate this imaging application, Monte Carlo (MC) simulations were performed for 10 different particles using a 5–10 cm spread out-Bragg peak (SOBP) centered on an 8 cm3, 3 mg/g Gd infused tumor. For a proton beam, 1.9 × 106 neutron captures per RBE weighted Gray Equivalent dose (GyE) occurred within the Gd tumor region. Antiprotons (bar{P}), negative pions (− π), and helium (He) ion beams resulted in 10, 17 and 1.3 times larger Gd neutron captures per GyE than protons, respectively. Therefore, the characteristic photon based spectroscopic imaging and secondary Gd dose enhancement could be viable and likely beneficial for these three particles.
Highlights
This study investigates the photon production from thermal neutron capture in a gadolinium (Gd) infused tumor as a result of secondary neutrons from particle therapy
The specific application of measuring the gadolinium neutron capture (GdNC) spectrum produced from proton therapy was previously termed Proton Neutron Gamma-X Detection (PNGXD)[8]
To investigate the effect of GdNC with the increase of treatment depth, a second configuration with 10–15 cm spread out-Bragg peak (SOBP), 5 × 5 cm[2] field size (FS), was employed for three particles. We investigated these three particles as they are the most clinically relevant particles, in addition, these particles can be compared to the simulation work published by Safavi-Naeini et al Using MCNP for these configurations, total dose, total neutron spectrum, thermal neutron production and the total Gd capture reaction rate were scored within the tumor
Summary
This study investigates the photon production from thermal neutron capture in a gadolinium (Gd) infused tumor as a result of secondary neutrons from particle therapy. As a result of particle therapy, secondary neutrons are produced and absorbed by Gd in the tumor providing potential enhanced localized dose in addition to a signature photon spectrum that can be used to produce an image of the Gd enriched tumor. When a high energy charged particle (> 50 MeV) with an impact parameter less than the atomic radius interacts with the target nucleus, neutrons in addition to other particles and light fragments can be driven out with high energy in the forward direction This process is referred to as the intranuclear cascade. The inelastic scattering process occurs when a high energy neutron (> 1 MeV) interacts with a target nucleus resulting in a change of system energy. This approach can be extended to include all heavy charged particles, a more general term, Particle Neutron Gamma-X Detection PNGXD is being proposed here
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