RADIOISOTOPES

Gafchromic® films (Ashland Inc.) have been widely used for dosimetry in radiation therapy using X rays and γ rays, and are now applied to the measurements and evaluations of various ion beams. A high-dose model, named HD-V2, is available to the measurements for the ion beams with the short-range penetrations, since its active layer is not laminated by a protection layer. However, an optical-density (OD) response curve of the film to the fluence must be determined for each ion species and its incident energy, because the response is not proportional to the fluence. In this paper, a simple method for obtaining the relative beam intensity distribution using the γ-ray dose response curve was studied on the basis of the similarity of ⁶⁰Co γ-ray and ion-beam irradiation response curves for the purpose of simplified measurements of the beam intensity distribution. We showed, as a result of the measurement using a flatbed image scanner ES-10000G, that the OD responses of various ion beams (selected ranges of linear energy transfer: 5.5 keV/µm–11 MeV/µm) corresponded to the ⁶⁰Co γ-ray irradiation response curve within certain OD ranges and that the range was up to about 0.7 and 0.5 in the red and green channels of the film, respectively. Thus, it is possible to obtain the relative intensity distribution of various ion beams using the γ-ray irradiation response curve without obtaining a response curve of each ion beam.