The reproducibility of large lead protected radiotherapy fields to the abdomen and pelvis

A series of patients treated with large, lead protected, abdomino-pelvic fields have been investigated, to identify field placement errors. Two hundred and forty-three machine verification films were performed on a total of 33 patients, and the films analysed. Important errors were detected resulting from field rotation, lateral shift and field width variations. Suggestions are made as to how these errors may be minimised in the future.