Comparative study on dosimetry of VMAT and IMRT in assisted radiotherapy after radical resection of rectal cancer

The present study compared the dosimetric differences of volumetric modulated arc therapy (VMAT) and 7-field intensity modulated radiation therapy technology (7F-IMRT) in assisted radiotherapy plan after resection of rectal carcinoma. Ten cases of patients at stages II–III of rectal cancer transabdominal resection with postoperative pelvic radiotherapy underwent 7F-IMRT and VMAT radiotherapy plan design using the CMS Monaco treatment planning system. We compared the dose distribution, the number of organs at risk and the number of machines in the two groups. The 7F-IMRT plans conformal index (CI) was 0.8319±0.0143 and VMAT plans CI was 0.838±0.164. Both plans reached up to the 95% isodose line at a volume of 100% planning target volume (PTV), the 7F- IMRT plans homogeneity index (HI) was 1.0760±0.0179, and the VMAT plans HI was 1.0821±0.0143. CI and HI had no statistical difference. With regard to S40, the V50 dose volume of the small intestine was endangered, and the VMAT plan was better than that of the 7F-IMRT plan, and the difference was statistically significant (P<0.05). The machine hop numbers of the two types of plans were 594.1±36.1 and 793.2 ±56.6 for for VMAT and 7F-IMRT, respectively. The VMAT plan was less than htat of the 7F-IMRT and the difference was statistically significant (P<0.05). Patients to whom VMAT techniques were utilized after resection of rectal cancer obtained an equal or a superior dose distribution compared with the IMRT plan. VMAT had important significance in protecting the small intestine, while significantly reducing treatment time.