Opportunistic dose amplification for proton and carbon ion therapy via capture of internally generated thermal neutrons

Abstract

This paper presents Neutron Capture Enhanced Particle Therapy (NCEPT), a method for enhancing the radiation dose delivered to a tumour relative to surrounding healthy tissues during proton and carbon ion therapy by capturing thermal neutrons produced inside the treatment volume during irradiation. NCEPT utilises extant and in-development boron-10 and gadolinium-157-based drugs from the related field of neutron capture therapy. Using Monte Carlo simulations, we demonstrate that a typical proton or carbon ion therapy treatment plan generates an approximately uniform thermal neutron field within the target volume, centred around the beam path. The tissue concentrations of neutron capture agents required to obtain an arbitrary 10% increase in biological effective dose are estimated for realistic treatment plans, and compared to concentrations previously reported in the literature. We conclude that the proposed method is theoretically feasible, and can provide a worthwhile improvement in the dose delivered to the tumour relative to healthy tissue with readily achievable concentrations of neutron capture enhancement drugs.

Figure 1

The simulation configuration used for pencil beam thermal neutron fluence estimation.

Figure 2

Photon-equivalent biological dose, physical dose and primary particle fluence (normalised to the total number of primary particles entering the phantom) resulting from 1 GyE carbon ion beam treatment of a 50 mm × 50 mm × 50 mm volume (100–150 mm depth); discrete beam energies range from 240–300 MeV/u in steps of 6 MeV/u). 2D slices and a 3D volume rendering of the dose distribution are also shown.

Figure 3

Normalised thermal neutron fluence resulting from irradiation of the 100 mm–150 mm target volume. Contour lines show fluence as a percentage of the maximum value in the slice, while the colourbars in the 3D figures show absolute fluence.