Analysis of positioning errors and weight variability in the radiation for head and neck cancer based on cone-beam computed tomography

Abstract

Objective To analyzed the effects of the positioning errors and weight variability of the head and neck cancer patients with intensity modulated radiation therapy (IMRT), or volumetric modulated arctherapy (VMAT) based on the kilovoltage cone-beam computed tomography (kV-CBCT). Methods CBCT images of 102 patients with head and neck cancer patients receiving IMRT or VMAT were screened by CBCT once a week for consecutively 6 weeks. The positioning errors were measured by comparing CBCT and planning CT in left-right (LR), anterior-posterior (AP) and cranio-caudal (CC) directions. Meanwhile, the weight of patients were measured every week. Results The positioning errors were (0.011 5±0.125 3) cm, (-0.017 6±0.123 3) cm and (-0.014 1±0.156 7) cm in LR, AP and CC directions, respectively. The mean systematic errors were all less than 0.02 cm in three axial directions, while the mean random errors were all within 0.2 cm. There was no statistically significant difference was observed among the setup errors in all three axial directions according to different week. Though the body weight of patients continued to drop during the radiation by with the mean weight loss of 3.5 kg and had a negative correlation with treatment course. Bivariate correlation analysis showed just the positioning errors in CC direction were significantly correlated with body weights loss. Conclusion There is no statistical relationship with in position errors of the patients with their treatment course, and the body weight loss seemed to influence the position errors in CC direction. Key words: Head and neck neoplasms; Radiotherapy; Setup errors; Cone-beam computed tomography