150-250 meV electron beams in radiation therapy.

High-energy electron beams in the range 150-250 MeV are studied to evaluate the feasibility for radiotherapy. Monte Carlo simulation results from the PENELOPE code are presented and used to determine lateral spread and penetration of these beams. It is shown that the penumbra is comparable to photon beams at depths less than 10 cm and the practical range (Rp) of these beams is greater than 40 cm. The depth dose distribution of electron beams compares favourably with photon beams. Effects caused by nuclear reactions are evaluated, including increased dose due to neutron production and induced radioactivity resulting in an increased relative biological effectiveness (RBE) factor of < 1.03.