Efficacy And Safety Of 3D Printing Template Assistant Computed Tomography-guided Radioactive ¹²⁵I Seed Implantation For Locally Recurrent Colorectal Cancer

OBJECTIVE:The present study aimed to explore the safety profile and clinical efficacy of computed tomography（CT）-guided radioactive ¹²⁵I seed（RIS）implantation assisted with three-dimensional printing template（3D-PT）in local recurrent colorectal carcinoma（LRCC）patients who previously received surgery or EBRT.METHODS:Fourteen patients（16 lesions）of LRCC received CT-guided RIS implantation in Affiliated Zhongshan hospital of Dalian University were enrolled in this present study between April 2017 to September 2020.There are 7 male and 7 female patients.The patients’median age was 64（range 50～78）years old.All the patients were pathologically diagnosed with primary colorectal cancer.The local recurrence lesions had clearly diagnosis.The median maximum diameter of the tumor was 4.65 cm（range 2.60 to 8.40 cm）.The surgical positions were 3 in the supine position and 13 in the prone position.All the patients have a history of surgery,50.0%（7/14）patients were treated with chemotherapy previously and 57.2%（8/14）patients had history of external beam radiation therapy（EBRT）.According to the process of expert consensus on3D-printing template assisted CT guided radioactive ¹²⁵I seed implantation,¹²⁵I seeds were implanted into the tumor,after exclusion of surgical contraindications.CT scans were performed 3 days after implantation.All the patients were followed up at 1,3,6,12 months and every 6 months afterword until December 2020.Therapeutic outcomes including local control,symptom relief and side effects,as well as dose parameters were retrospectively evaluated.Kaplan-Meier survival analysis was used to estimate long time survival.Log-rank test was performed to compare the differences.The receiver operating characteristic（ROC）curve was used to analyze the optimal cutoff values.RESULTS:The follow-up period ended in December 2020.The median follow-up time was 12.0 months（range 3～29 months）.The median number of RIS was 49,ranging from 23 to 152.The median radioactive activity of a single RIS was 0.65 m Ci（range0.50～0.80 m Ci）.The median local control time was 11.0 months（range 3～22months）.At 12 months of follow-up,there were 3 cases of complete remission（CR）,6cases of partial remission（PR）,3 cases of stable disease（SD）,and 4 cases of disease progression（PD）.The LC rates at 3,6,and 12 months after surgery were 100.0%,87.5%,and 75.0%,respectively.The overall response rate（CR+PR）was 56.3%.The median overall survival（OS）time was 12 months,and the 1-year and 2-year OS rates were 64.3%and 21.4%,respectively.At 12 months after surgery,the therapeutic response results of 8 patients（9 lesions）who have received radiotherapy in the past,the total remission rate was 66.6%;the local control rate was 77.8%;the pain relief rate was83.3%.The results of dose parameters showed that the average postoperative D₉₀（dose covering 90%of the target volume）was lower than the prescribed dose,and the difference was statistically significant（P=0.03）.Further analysis showed that the D₉₀and D_90difference(preoperative D₉₀-postoperative D₉₀)significantly affected the local control time（P=0.018 and 0.033）.The LC rate was remarkably improved in D₉₀>128.55 Gy and D_{90 difference}<15.50Gy.Painless duration time ranged from 0 to 18months（median 7 months）.The 12 months response rate of pain relief was 77.8%（7/9）.The comparison of scores showed that the pain was significantly relieved at 1 month,3months,6 months,and 12 months after seed implantation（P<0.01）.No ¹²⁵I seeds migrated to other tissues or organs.No serious adverse events（≥grade 3）occurred.Only 1 case（7.1%1/14）had grade 2 radiation colorectal mucosal reaction,which was a patient who had received external radiation therapy previously.CONCLUSIONS:CT-guided RIS assisted with 3D-PT is an effective and safe salvage treatment strategy for patients with LRCC after EBRT or surgery.