Abstract: PURPOSE: To explore the value of metal artifact reduction(MAR) algorithms on radiotherapy dose calculation by comparing the CT values and radiation doses before and after MAR. METHODS: Twenty head and neck cancer patients admitted to Shanghai Ninth People's Hospital,Shanghai Jiao Tong University School of Medicine during Oct 2019 to March 2020 were selected. All of them underwent mandibular reconstruction with titanium plate implantation before radiotherapy. Their CT simulation scans and the images after MAR were collected. The organs at risk(OAR) were contoured by auto-segmentation software on CT images after MAR and the contouring was duplicated to original CT scan, with both the CT values of OAR recorded. Two 40 cm×40 cm opposite irradiated fields were planned with anterior margin of the second cervical vertebra set as central point, and then dose calculations were collected for paired t test with SPSS 21.0 software package. RESULTS: The average CT values of all the organs and tissue changed significantly after MAR based on MAR algorithms, compared with the original planning CT images. The average rate of change was 26.29%, with a range from 5.04%-127.19%.There was significant difference in average CT values of organs between before and after MAR except for larynx, bilateral parotid glands, pharyngeal tonsil, pituitary gland and thyroid gland. There was no significant difference in radiation dose change between the two groups, with the exception of oral cavity. CONCLUSIONS: MAR algorithms can effectively reduce metal artifacts on CT scans, but the CT values were also significantly changed, which inevitably influenced the dose calculation. It is suggested that CT images after MAR could be performed as references for target area contouring, but not suitable for dose calculation for planning of radiotherapy.

Key words: Metal artifact reduction algorithms, Head and neck cancer, CT value, Dosimetry, Titanium plate, Metal implantation