Neutron capture enhances dose and reduces cancer cell viability in and out of beam during helium and carbon ion therapy

Purpose Neutron Capture Enhanced Particle Therapy (NCEPT) is a proposed augmentation of charged particle therapy which exploits thermal neutrons generated internally, within the treatment volume via nuclear fragmentation, to deliver a biochemically targeted radiation dose to cancer cells. This work is the first experimental demonstration of NCEPT, performed using both carbon and helium ion beams with two different targeted neutron capture agents (NCAs). Materials and Methods Human glioblastoma cells (T98G) were irradiated by carbon and helium ion beams in the presence of NCAs, [ 10 B]-BPA and [ 157 Gd]-DOTA-TPP. Cells were positioned within a PMMA phantom either laterally adjacent to, or within, a 100×100×60 mm spread out Bragg peak (SOBP). The impact of NCAs and location relative to the SOBP on the cells was measured by cell growth and survival assays in six independent experiments. Neutron fluence within the phantom was characterised by quantifying the neutron activation of gold foil. Results Cells placed inside the treatment volume reached 10% survival by 2 Gy of C or 2-3 Gy of He in the presence of NCAs compared to 5 Gy of C and 7 Gy of He with no NCA. Cells placed adjacent to the treatment volume showed a dose-dependent decrease in cell growth when treated with NCAs, reaching 10% survival by 6 Gy of C or He (to the treatment volume), compared to a no detectable effect on cells without NCA. The mean thermal neutron fluence at the centre of the SOBP was approximately 2.2×10 9 n/cm2/Gy(RBE) for the carbon beam and 5.8×10 9 n/cm2/Gy(RBE) for the helium beam and gradually decreased in all directions. Conclusions The addition of NCAs to cancer cells during C and He beam irradiation has a measurable impact on cell survival and growth in-vitro . Through the capture of internally generated neutrons, NCEPT introduces the concept of a biochemically targeted radiation dose to charged particle therapy. NCEPT enables the established pharmaceuticals and concepts of neutron capture therapy to be applied to a wider range of deeply situated and diffuse tumours, by targeting this dose to micro-infiltrates and cells outside of defined treatment regions. These results also demonstrate the potential for NCEPT to provide an increased dose to tumour tissue within the treatment volume, with a reduction in radiation doses to off target tissue.