Motoharu Sasaki

Impact of changes in body contours on radiation therapy dose distribution after uterine cervical cancer surgery

Patients receiving postoperative irradiation for uterine cervical cancer might not be able to eat during radiation therapy because of the effects of concurrent chemo-radiotherapy; this may lead to changes in the patient's body shape during treatment. When performing image-guided radiotherapy, it is necessary to determine immediately whether treatment can be performed on the day or whether re-planning is required. The purpose of this study was to determine indicators for re-planning by examining the effects of changing body contours on radiation therapy dose. The original body contour was reduced by 1 cm in the front portion (structure-set 1). Based on the original dose distribution, the dose recalculation was performed with a structure set created using the body contour of structure-set 1. The difference between the original and recalculated dose distributions of structure-set 1 was evaluated through gamma analysis (GA). In the GA results for dose distribution obtained via recalculation with structure-set 1, a pass rate of 90% or more was obtained for a criterion of 2 mm/2% in all cases. The results suggest that dose re-planning is rarely required when the body shape is reduced by only 1 cm in the front.