Studies on adjustment inaccuracies in telecobalt therapy of gynecological tumors

Quality assurance in radiotherapy includes always problems concerning the execution of irradiation. Nonsystematic adjustment inaccuracies of biaxial high-voltage pendulum irradiation of gynecological tumors were investigated and the effects of nonsystematic faults in irradiation on shape and position of the 80% isodose on the graphic display of the microcomputer system K 1630 were demonstrated. Dose deviations for some points at the target volume or its vicinity (bladder, rectum) were calculated additonally. The adjustment inaccuracies were according to the literature ± mm in marking of the pendulum axis. The effects of radiotherapy with erroneous pendulum angle were also examined as well as combined adjustment inaccuracies. Some of the specified nonsystematical incorrect adjustments revealed considerable, up to two-figure per cent dose fluctuations in erroneous irradiation in the same way througout the whole irradiation series