Dosimetric characteristics of an improved radiochromic film.

Recently, a new model of radiochromic film has been developed for medical applications to provide a higher sensitivity and better uniformity of response than existing models (i.e., MD-55). Dosimetric characteristics including sensitivity, linearity, reproducibility, uniformity, and dependence on energy and time have been studied experimentally. The characteristics of the new films were compared with those of model MD-55. For these investigations, the two films were exposed to ionizing radiation in the dose range from 1-72 Gy, using gamma-rays from a 60Co teletherapy unit and 6- and 18-MV x rays from a linear accelerator. The response of the exposed film was measured with a helium-neon laser densitometer. The results indicated that the sensitivity of the improved film was about 40% greater than that of MD-55 film. Moreover, the response of the improved film was found to be uniform within 4% only in one direction of the film. The orthogonal direction indicated a nonuniformity of up to 15%, similar to that of model MD-55. Less than 5% energy dependence in the megavoltage photon range was observed for the new film. Complete dosimetric characteristics of the new film are presented.