Characterization of new portal film systems for radiotherapy verification.

Portal images are an important verification tool in radiotherapy. Their use has been limited by their poor image quality, which is due to the inherent lack of contrast at megavoltage energies. Recently CEA and Kodak have introduced new portal film-cassette systems with much improved contrast. We have determined the H-D curves for these systems and found the gamma (gamma) for the CEA system (8.5) to be larger than that for the Kodak EC-L system (6.3). The optimal doses were CEA TLF 1.2 cGy, CEA TVS 15.9 cGy and Kodak EC-L 1.5 cGy. We also obtained phantom images that were evaluated by 11 radiotherapists. They ranked the CEA B High Plus cassette with CEA TVS film the highest, followed by the Kodak EC-L system. Some clinical films of a lateral pelvis are also presented, to demonstrate the improvement in image quality with these new film systems as compared with conventional portal films.