Abstract: Objective To analyze and compare the dosimetric difference between helical tomotherapy (TOMO) and volumetric modulated arc therapy (VMAT) in postoperative patients with bladder cancer, so to provide a reference for optimal radiotherapy technique for this disease. Methods Ten bladder cancer patients with who were received radiotherapy after transurethral bladder tumor resection (TURBT) from January 2019 to December 2019 in Peking Union Medical College Hospital were included. Clinical target volume (CTV) and organ at risk (OAR) were delineated on the CT images, and then the TOMO plans and the VMAT plans were designed, respectively. The difference was evaluated by D95%, Dmean, Dmax, Dmin, and CI, HI of the target volume, and V20, V30, V40, D5, D10, Dmean and Dmax of the rectum, small intestine, pelvic bone marrow, femoral head and other OARs. Results Both TOMO and VAMT plans met the clinical dosimetry needs, and the Dmean, Dmax, Dmin and HI of the target volume of the TOMO plans were better than those of the VMAT plans (all P＜0.05). In terms of OARs, TOMO plans were better than VMAT plans, as comparing to the V20 and V30 of small intestine, Dmax of the right femoral head, Dmax of the rectum, Dmean and Dmax of the pelvic bone marrow(P＜0.05). Conclusions For bladder cancer patients who received radiotherapy after TURBT, both the TOMO plans and VMAT plans can achieve the clinical dosimetry needs, but the TOMO plans exhibit more dosimetry advantages, better target volume conformity and uniformity, and lower exposure of OARs. These results may function as a potential reference for the choice of radiotherapy plan for bladder cancer patients.

Key words: bladder cancer, radiotherapy, dosimetry, helical tomography, volumetric modulated arc therapy