Analyse rétrospective de la reproductibilité de la mise en place quotidienne des champs dʹirradiation de cancer du rectum par imagerie de contrôle de haute énergie

SummaryPurpose luate a ionization chamber on-line portal imaging system in routine clinical radiotherapy of rectum cancers. ts and methods lt portal images were obtained using a fast electronic megavoltage radiotherapy imaging system in 13 cases of pelvic fields. A total of 208 portal images and 13 simulator films were used to determine the values of set-up deviations in the X-Z directions of a fixed co-ordinate system, and of the rotation fields (R). s tandard deviations of the difference between simulation and treatment images were 3.2 mm and 0.9 mm for X and Z, 3.6 mm for the rotation fault. The standard deviations were, respectively, 7.1 mm, 7.1 mm and 1.5 mm. The cumulative frequency distributions revealed that 80% and 95% of the absolute differences were less than 10 mm and 17.5 mm, respectively. sion results indicate the difficulty of a reproducible daily set-up. A weekly control could be proposed in order to increase the quality of pelvic site treatment. The introduction of masks to improve the set-up is also discussed.