[CT guidance ¹²⁵I seed implantation for pelvic recurrent rectal cancer assisted by 3D printing individual non-coplanar template]

Objective: To analyze the difference of dosimetric parameters between pre-plan and post-plan of ¹²⁵I radioactive seed implantation assisted by 3D printing individual non-coplanar template (3D printing template) for locally recurrent rectal cancer (LRRC). Methods: From February 2016 to April 2016, a total of 10 patients with locally recurrent rectal cancer received ¹²⁵I seeds implantation under CT guidance assisted by 3D printing template in Department of Radiation Oncology, Peking University Third Hospital.Each patient underwent CT simulation, three-dimentional treatment planning pre-implantation, 3D printing template design, radioactive seed implantation assisted by 3D printing template and dosimetric verification post implantation. The median activity of seed was 0.63 mCi (0.58 to 0.7 mCi) (2.15- 2.59×10⁷ Bq), and the median number of seeds was 80 (19 to 192). D₉₀, D₁₀₀, V₁₀₀, V₁₅₀, CI, EI, HI, D_5cc, D_2cc of bladder and bowel of pre-plan and post-plan were calculated, respectively.Paired t test was used to evaluate the difference of dosimetric parameters between pre-plan and post-plan. Results: The median D₉₀ of pre-plan and post-plan were 13 761.0 and 12 798.8 cGy, respectively.The median D₁₀₀ of pre-plan and post-plan were 5 293.6 and 5 397.9 cGy, respectively.The median V₁₀₀ of pre-plan and post-plan were 90.0% and 90.0%, respectively.The median V₁₅₀ of pre-plan and post-plan were 63.8% and 62.4%, respectively.The median CI of pre-plan and post-plan were 0.73 and 0.67.The median EI of pre-plan and post-plan were 0.22 and 0.30, respectively. The median HI of pre-plan and post-plan were 0.29 and 0.31.The median bladder D_2cc of pre-plan and post-plan were 3 088.8 and 4 240.4 cGy, respectively.The median bowel D_2cc of pre-plan and post-plan were 7 051.6 and 7 903.9 cGy, respectively. Conclusions: 3D printing template might be helpful for locally recurrent rectal cancer patients who received ¹²⁵I radioactive seed implantation assisted by 3D printing individual template.Seed implantation might have more chances to achieve prescription dose and dose limitation of organs at risk of pre-plan, which is important for precise implantation and quality control.