Accuracy in mantle field irradiations: irradiated volume and daily dose

Accuracy of patient positioning and dose delivery in mantle field irradiations was investigated on 29 patients treated between August 1990 and December 1991. Patients were treated in two different centers, University Hospital St. Rafaël in Leuven and Institut Gustave Roussy in Villejuif, where different techniques and procedures were used. Measurements were performed on 341 portal films and entrance doses were measured in 518 treatment set-ups. The impact of systematic errors occurring during treatment preparation and day-to-day variations on the accuracy of treatment execution were separately analysed. Daily reproducibility, defined as the deviation from the respective mean measured value for a treatment was demonstrated to be good for both the treated volume and the delivered dose and no difference between the two techniques was shown. Comparing the successive portal films of individual patients (reproducibility of a treatment, once it has started), only small day-to-day variations are found: the SD is 3.4 mm for craniocaudal movements and 2.6 mm for lateral movements. For dose delivery very narrow distributions are obtained with SDs of, respectively, 1.5% and 1.85% for the Leuven and the Villejuif group. This suggests that the position of the patient, which is often thought as the critical point in this complex set-up can be done in a very accurate way, regardless of the position used. To assess the global accuracy of the treatment, the actually treated volume and delivered dose were compared with the planned values. Apart from reproducibility this also takes into account the whole preparatory procedure between planning and the start of the therapy (first session).(ABSTRACT TRUNCATED AT 250 WORDS)