The effect of enforced fixed-field on the delivery accuracy of IMRT in the treatment of cervical cancer patients

Abstract

The purpose of this study is to investigate delivery accuracy and dosimetric distribution between a fixed jaw technique (FJT) and split-field technique (SFT) intensity modulated radiotherapy (IMRT) for cervical cancer patients. Delivery accuracy of FJT and SFT IMRT plans was investigated using a Mapcheck on 15 cervical cancer patients. Dosimetric distributions on target coverage and organ at risk (OAR) sparing were also compared. The average gamma passing rate (%GP) for SFT and FJT IMRT plans were 99.30% ± 0.89% and 96.91% ± 2.93% (p < 0.01), respectively. %GP less than 85% was observed for FJT IMRT plans. %GP was highly correlated with field width and field size for FJT plans with Pearson correlations of r = −0.60 (p < 0.001) and −0.56 (p < 0.001), respectively. The target coverage for FJT and SFT IMRT were 99.36% ± 0.36% and 99.40% ± 0.32%, respectively (p = 0.43). For planning target volume point dose D50, D2 and mean dose (Dmean), the absolute values were very close between two techniques with a difference within 2%, indicating little clinical significance. FJT IMRT irradiated a bit higher maximum dose on spinal cord than split-field did (p = 0.001), there was no other significant dosimetric difference between SFT and FJT IMRT plans on OAR sparing. FJT IMRT achieved significantly lower monitor unit (MU) and delivery time. In a conclusion, FJT affects the delivery accuracy of IMRT, although it decrease the total MU and delivery time with similar dose distributions compared with SFT IMRT. More attention should be put on the delivery accuracy when applying FJT IMRT for large field cervical cancer patient.