Quality of portal verification radiography using EC-L film in electron beam therapy

The quality of the portal verification radiographs produced using the enhanced-contrast localisation (EC-L) Fast cassette-EC-L film (F-EC) combination and the EC-L Oncology cassette-EC-L film (O-EC) combination was investigated fundamentally and clinically. A computerised radiography (CR) system was used for comparison. In the clinic, portal verification radiographs produced for 22 patients with breast cancer were evaluated. The characteristic curves showed that the relative speed was 0.92 for the O-EC combination when the speed of the F-EC combination was defined to be 1, and that the average gradients were 4.76 and 4.35 for the F-EC combination and the O-EC combination, respectively. The smallest visible volumes of Burger's phantom were 50.3 mm(3), 60.8 mm(3) and 199.5 mm(3) for the F-EC combination, the O-EC combination and the CR system, respectively, at an energy of 9 MeV, and 68.4 mm(3), 74.2 mm(3) and 195 mm(3), respectively, at an energy of 12 MeV. In the clinic, both combinations at an energy of 6 MeV and the O-EC combination at 9 MeV showed very poor quality owing to underdensity. However the F-EC combination at an energy of 12 MeV and the O-EC combination at an energy of 15 MeV demonstrated a higher quality. When bremsstrahlung dose passing through the body is sufficient, the quality of portal verification radiography using EC-L film is appropriate for clinical use.