Neutron production from electron accelerators used for medical purposes

Abstract

A matter of growing concern amongst users of electron accelerators for medical application is the problem of photoneutron production in target and collimating assemblies and the consequent whole body neutron dose to a patient undergoing radiotherapeutic treatment. Measurements on a 35 MeV linear accelerator constructed by the M.E.L. Equipment Company Limited indicated that the neutron dose-equivalent rate in the x-ray beam was of the order of 0.5% of the central axis x-ray absorbed dose rate. Measurements reported by various workers on betatrons lead to values between 1.0 and 3.0% (Frost and Michel 1964). Various manufacturers in the United Kingdom and other countries are now supplying accelerators capable of operating in the 15-45 MeV range which will give rise to neutron production. There is an additional complication in that photoneutrons produced by high energy photons incident on the patient contribute to patient dose.Rough calculations based on measurements of photoneutron production by Barber and George (1 959) lead to the results shown in table 1.

Measurement of fast neutrons produced by high-energy X-ray beams of medical electron accelerators

“…The present work is in disagreement with the 32 MeV betatron measurements of Lofgren and Spring (1970), who observed a very low neutron fluence (1.8 x 103 n cm-2 rad-1) both inside and outside the beam (to a distance of 7 cm), except for a higher value (5.1 x 103 n cm-2rad-1) at the central ray. The results of Axton and Bardell (1972) indicate neutron production from both a 33 MeV betatron and a 16 MeV linac to be lower than that from the accelerators used in this study or in that of Robinson and Kehrer (1972). However, Axton and Bardell (1972) do not state their treatment distance or the location of their detector external to the X-ray field; consequently, a comparison may not be meaningful.…”

“…The results of Axton and Bardell (1972) indicate neutron production from both a 33 MeV betatron and a 16 MeV linac to be lower than that from the accelerators used in this study or in that of Robinson and Kehrer (1972). However, Axton and Bardell (1972) do not state their treatment distance or the location of their detector external to the X-ray field; consequently, a comparison may not be meaningful.…”

“…A considerable 1.4 100 amount of effort has been devoted to accurate dosimetry of the photon and electron beams from these accelerators, but relatively few measurements have been reported for the associated neutrons. Furthermore, all previous neutron studies were done with betatrons rather than with linear accelerators, except for some recent 16 MeV linac measurements which were published during the course of this study by Axton and Bardell (1972).…”

Electron linear accelerators for radiation therapy: history, principles and contemporary developments

“…Neutron hazards from higher energy X-ray and electron therapy beams (up to 35 MeV) need to be considered. Here photoneutrons are produced in the target and the collimator as well as in the patient and are found as a contaminant both within and outside the useful beam, Recent measurements (Axton and Bardell 1972) are in reasonable agreement with calculations of the neutron dose equivalent and were found t o be about 0.5% of that from the useful beam of X-rays (16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33) and substantially less for electron beams (see also Dealler 1969).…”

Characterization and utilization of a Bonner sphere set based on gold activation foils

“…Gold is the most commonly used material, and this work describes the characterization of a BS set based on gold foils, and its use to measure the contaminant neutron spectrum in the vicinity of a hospital electron LinAc used for cancer therapy where the radiation field is pulsed, has an high photon component, and the neutron spectrum extends over a wide energy range. The paper describes a continuation of work with gold-foil-based BSs at NPL (1,2) . It presents further validation of the response functions of the sphere set thus enabling other users to build and use BSs of the same design without the need for extensive characterization of response functions.…”