Neutron-induced Carcinogenic Effects (NICE)—an examination of the biophysics underlying neutron carcinogenesis

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Our research aims to improve our understanding of the biophysical effects surrounding neutron dose deposition in human tissue. Neutrons are encountered in space, at nuclear power plants, in various industrial applications, and in radiation therapy (RT). Radiological protection measures are designed to protect human populations from the risk that neutrons (and other forms of radiation) pose. While these measures are generally adequate, they cannot protect patients undergoing RT. Neutrons that are generated as by-product, radiation during high-energy (>10 MeV) photon- and proton-beam RT, cannot be shielded and consequently exposed patients are susceptible to radiation-induced carcinogenesis. The risk is well known and generally accepted, although poorly understood. Efforts currently underway to introduce proton beam RT into Canada have brought the issue into focus. Paediatric patients who are considered the main beneficiaries of proton RT are also the most at risk for second malignancies resulting from the unavoidable whole body dose of secondary radiation that arises in part from neutrons. Recent research by the PI and his former student Robert Maglieri has demonstrated that the Canadian-made Nested Neutron Spectrometer (Detec Inc., Gatineau, Quebec) may be used to measure the energy spectra of neutrons from RT beams. Our report (Maglieri et al., 2015) into the first use of this active neutron detector in the radiation field of a medical linac has opened the possibility for practical neutron spectral measurements in RT. In light of, and motivated by, our new measurement technique, an improvement in our understanding of the energy-dependent carcinogenic potential of neutrons would allow us to convert our physically-measured neutron energy spectra into biologically-meaningful dose estimates. One practical way to advance our understanding of the fundamental biophysics underlying the energy-dependent carcinogenic potential of neutrons is to examine, at the macrodosimetric and nanodosimetric scales, neutron dose deposition processes as a function of energy. This type of work has been done by other groups to study radiation damage by photons and protons. We thus propose a Monte Carlo track structure study of neutron dose deposition at the DNA-scale coupled with actual measurements of neutron spectra and of neutron DNA damage in cells, in vitro. We have access to Monte Carlo expertise, RT equipment and to the neutron beams and radiobiological facilities of our collaborators at Canadian Nuclear Laboratories, Chalk River, Ontario. All considered, we are uniquely positioned with the experience, the facilities, and the motivation to measure neutron energy spectra and to convert them into biologically-meaningful dose estimates. Missing is an understanding of the energy-dependent carcinogenic potential of neutrons. Improving this understanding is the goal of our proposed research.