Radiometry of 3 different radiotherapies for rectal cancer before operation

Objective To provide the evidence for the selection of radiotherapy for rectal cancer before operation by comparing the radiometry characteristics of helical tomotherapy (HT), step-and-shoot intensity-modulated radiotherapy (IMRT) and 3-dimensional conformal radiotherapy (3DCRT). Methods Ten patients with stage Ⅱ-Ⅲ rectal cancer underwent HT, 9-feld IMRT and 3-feld 3DCRT at the dose of 56.25 Gy for the pGTV and at the dose of 50 Gy for the PTV in 25 fractions. The dose distribution in target areas and involved organs was assessed according to the dose-volume histogram. Results The 3 radiotherapies could meet the prescribed dose for the target areas. IMRT and HT but not 3DCRT could meet the prescribed dose for the involved organs. The conformity index (CI) of 3DCRT for the target areas (pGTV and PTV) was higher than that of IMRT and HT (P< 0.05) and the homogeneity index (HI) of HT for the pGTV was lower than that of IMRT and 3DCRT (P< 0.05), indicating that IMRT and HT protect the involved organs better than 3DCRT, and HT protects the involved organs better than IMRT. The intestine V15 was 304.7 cc, 283.5 cc and 240.7 cc, respectively, for 3DCRT, IMRT and HT. Conclusion 3DCRT cannot meet the prescribed dose for the involved organs. IMRT and HT are signifcantly advantageous over 3DCRT in conformity of target areas and protection of involved organs. The effect of HT is better than that of IMRT and 3DCRT in reducing the irradiation dose for intestine, bladder, pelvic and femoral head.