Room: AAPM ePoster Library
Patients receiving 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 the treatment period. When performing image-guided radiotherapy, it is necessary to immediately determine whether the treatment can be performed on the day or re-planning is required. The purpose of this study was to determine indicators of re-planning by examining the effects of changing body contours on the radiation therapy dose.
The original body contour was reduced by 1 cm in the front portion (Structure-set 1) and by 1 cm in all directions except the back (Structure-set 2). Based on the original dose distribution, the recalculated dose distribution was performed using a structure set created using the body contours of Structure-set 1 and Structure-set 2. The difference between the original and recalculated dose distributions of the two structure-sets was evaluated through gamma analysis (GA).
When the body contour was reduced by 1 cm only in the front, a pass rate of 90% or more was obtained through GA, with a criterion of 2 mm/2% in all cases. In contrast, when the body contour was reduced by 1 cm in all directions except the back, significant differences in the dose distribution that varied from each other were observed in each case.
Our results suggest that dose re-planning is rarely required when the body shape is reduced by only 1 cm in the front.