The authors have adapted the age-diffusion model proposed by Kawachi (ibid., vol.20, p.571 (1975)) and later modified by Steben, Ayyangar and Suntharalingam (1977) to parametrise the Brown Boveri Asklepitron 45 electron beams, to obtain the parameters for the Sagittaire linear accelerator electron beams introducing the necessary modifications in the dose equation. The dose equation used by Steben et al. is given.