[Dosimetric comparison between helical tomotherapy and step-and-shoot intensity modulated radiation therapy for...

Helical tomotherapy (HT) has shown its dosimetric advantages in the radiotherapy for many cancers. To date, no published studies have performed a dosimetric evaluation of whole pelvic radiotherapy (WPRT) using HT for postoperative endometrial cancer. This study was to compare the dosimetric characteristics of HT and step-and-shoot intensity modulated radiation therapy (SaS-IMRT) for endometrial cancer patients undergoing postoperative WPRT, and to explore whether whole pelvic HT for postoperative endometrial cancer has the advantage of dosimetry.

Ten patients with endometrial cancer undergoing postoperative WPRT were enrolled in this study. SaS-IMRT and HT Plans were developed for each patient. The dose distributions of the targets, organs at risk and normal tissue were analyzed and compared.

The mean PTV100 were 95.6% and 95.8% (P=0.72) for the SaS-IMRT and HT plans, respectively. The mean homogeneity indexes were 1.10 and 1. 07 (P=0.00). The mean conformity indexes were both 0.87. The mean doses to rectum and bladder for HT were decreased by 1.3 Gy and 3.0 Gy compared with SaS-IMRT, respectively, while the mean dose to pelvic bones was increased by 1.1 Gy. The volumes of small intestine and colon, pelvic bones receiving moderate and low dose also increased. The V5, V10 and V20 of normal tissue were increased by 13.0%, 18.0%, and 5.0% (P=0.00). The mean dose to normal tissue was increased by 2.5 Gy (P=0.00).

Compared with SaS-IMRT, HT resulted in more homogeneous PTV dose distribution, better sparing of rectum and bladder. The volumes of small intestine and colon, pelvic bones and normal tissue receiving moderate and low dose for HT increased. The clinical significance of the dosimetric differences needs further investigations.