RELIABILITY OF CLINICAL PORT FILMS FOR MEASURING DOSE INHOMOGENEITIESIN RADIOTHERAPY FOR HEAD AND NECK TUMORS

Reproducibility and reliability of film dosimetry are evaluated in cli nical circumstances. Optical densities were read on 82 routinely taken verification films of Ear-Nose-Throat (ENT) treatment fields and corr ected with the sensitometric curve to obtain relative dose values. Off -axis ratios measured on 10 successive films of one specific field wer e compared with each other and show a good reproducibility (s = 1.7%). Reliability was assessed by comparing 82 off-axis ratios obtained on the films with off-axis ratios obtained by simultaneously performed di ode measurements. Only small relative differences were detected (xBAR = 1.1%, s = 3.0).