Neutron activation of gadolinium for ion therapy: a Monte Carlo study of charged particle beams

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 cm 3 , 3 mg/g Gd infused tumor. For a proton beam, 1.9 × 10 6 neutron captures per RBE weighted Gray equivalent dose (Gye) occurred within the Gd tumor region. Antiprotons (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.

Radiobiological impact of gadolinium neutron capture from proton therapy and alternative neutron sources using TOPAS‐nBio

“…Using the microdosimetric strand break results determined from within this study, a total of effectively 1.8 × 10 8 SSBs and 6.8 × 10 6 DSBs for 1 Gy of proton dose can be calculated. From results produced in another MC simulation study, a 5–10 cm SOBP beam of protons, carbon ions, and helium ions incident on an 8 cm 3 volume of 3000 PPM Gd resulted in 2.1 × 10 6 , 1.1 × 10 6 , and 3.7 × 10 6 neutron captures per Gy of absolute dose 20 . Therefore, the total strand breaks can be calculated as: 8.2 × 10 7 SSBs, 3.1 × 10 6 DSBs for protons, 4.3 × 10 7 SSBs, 1.6 × 10 6 DSBs for carbon ions and 1.5 × 10 8 SSBs, 5.5 × 10 6 DSBs for helium ions.…”

“…The results for the three highest thermal neutron production values were from helium ions, antiprotons, and negative pions with values of 1.3 × 10 6 , 1.4 × 10 7 , and 2.9 × 10 7 (cm −2 ) per Gy of dose. A value of 7.4 × 10 5 (cm −2 ) thermal neutrons per Gy of proton dose was determined within this study 20 . Several studies have measured the thermal neutron fluence (cm −2 ) production per Gy of proton dose at various distances away from the isocenter.…”

Neutron Source Based on Vacuum Insulated Tandem Accelerator and Lithium Target

“…The BSA consists of a magnesium fluoride moderator, a composite reflector (graphite in the front hemisphere and lead in the back), an absorber, and a filter. Monte Carlo radiation transport tools are used to design and optimize a neutron source [24][25][26][27][28], X-ray-radian-and gamma-radianbased systems [29,30]. Numerical simulations of neutron and γ-radiation transport showed that at a proton beam energy of 2.3 MeV, the BSA makes it possible to produce a neutron beam with parameters well-matching the BNCT requirements [31,32].…”

Boron-Based Neutron Scintillator Screens for Neutron Imaging

“…Additionally, 10 B's daughter products are more massive and deposit their energy over a shorter range than those of 6 Li: Natural gadolinium, which consists of seven stable isotopes, has a total thermal neutron cross-section of 48,800 barns. Two isotopes that have high thermal neutron capture cross-sections and a relatively high natural abundance are 155 Gd (60,900 b, 14.8% abundance) and 157 Gd (254,000 b, 15.7% abundance) [40]. As shown in Equations ( 4) and ( 5), gadolinium neutron absorption reactions produce prompt γ-rays and internal conversion electrons (IC e− ), which also produce secondary characteristic X-rays and Auger electrons, including Coster-Kronig electrons.…”

“…Thermal neutron capture by 157 Gd, for example, releases an average of 3.288 photons including prompt and secondary γ-rays and X-rays with energies ranging from 10s of eV up to several MeV and a mean energy of 2.394 MeV [42,43]. This same reaction also releases IC e− with energies ranging from 29 keV to 6.9 MeV, with the most intense discrete IC e− emissions of 29 and 71 keV [40,43,44]. The range of a 71 keV IC e− in gadolinium is approximately 20 µm [45].…”