M6型射波刀立体定向放疗系统图像引导照射剂量研究

Study on radiation dose of Cyberknife M6 stereotactic radiotherapy image guidance system

目的:分析M6型射波刀立体定向放疗(stereotactic radiotherapy,SBRT)图像引导系统产生的照射剂量及影响因素,为接受M6型射波刀治疗肿瘤患者额外照射剂量提供参考依据。方法:回顾性分析天津医科大学肿瘤医院2023年1月1日至2023年5月31日216例采用M6型射波刀SBRT的肿瘤患者,将患者按照图像引导方式和肿瘤靶区位置进行分类,分别统计患者肿瘤靶区的照射剂量、治疗分割次数、球管曝光参数、计算球管总曝光次数、累积的照射剂量,得出不同图像引导方式和治疗部位平均曝光次数、平均照射剂量,与患者肿瘤靶区的照射剂量相比较,并勾画ROC曲线取肿瘤体积及BED_(10)的cutoff值进行分层,利用多元线性逐步回归模型分析累积剂量的影响因素。结果:颅骨(6D-skull)追踪方式,椎体(x-sight)追踪方式,同步呼吸(sychrony)追踪方式,金标(fiducial)追踪方式,肺追踪(x-sight lung)肿瘤患者平均曝光次数、平均累积照射剂量(cGy)、累积照射剂量/靶区照射剂量(%)分别为131次、1.6 cGy、0.02%~0.18%;212次、8.0 cGy、0.05%~0.45%;322次、12.2 cGy、0.06%~0.62%;237次、10.1 cGy、0.07%~0.36%;411次、12 cGy、0.20%~0.21%。颅脑、胸部、腹部、盆腔肿瘤患者的平均曝光次数、累积照射剂量(c Gy)、累积照射剂量/靶区照射剂量(%)分别为131次、1.6 cGy、0.02%~0.18%;258次、9.6 cGy、0.05%~0.62%;191次、7.7 cGy、0.08%~0.44%;209次、8.5 cGy、0.07%~0.36%。ROC曲线中按照肿瘤体积(cutoff值30 mL)和BED_(10)(cutoff值60 Gy)进行分类,发现肿瘤部位、靶区体积、BED_(10)均为累积照射剂量的影响因素。当肿瘤体积≥30 mL、BED_(10)>60 Gy、肿瘤位于胸、腹、盆腔时,累积剂量增大。结论:采用颅骨(6D-skull)追踪方式颅脑肿瘤患者平均曝光次数、累积照射剂量最低,采用其余4种图像引导方式对应的胸部、腹部、盆腔肿瘤患者平均曝光次数、累积照射剂量接近。肿瘤部位、靶区体积、BED_(10)均为累积照射剂量的影响因素。M6型射波刀SBRT系统能够对患者治疗过程中进行实时位置精度验证,患者接受的辐射剂量较小。

Objective:To analyze the radiation dose and influencing factors generated by the Cyberknife M6 stereotactic radiotherapy image guided system and provide a reference for additional radiation doses in tumor patients undergoing M6 Cyberknife stereotactic radiotherapy treatment.Methods:A retrospective analysis was conducted on 216 tumor patients who underwent Cyberknife M6 stereotactic radiotherapy at Tianjin Medical University Cancer Institute&Hospital from January to May 2023.Patients were classified according to image guidance methods and treatment sites,irradiation dose,treatment segmentation times,and tube exposure parameters of the tumor target area.Total exposure times and cumulative irradiation dose were calculated,and the average irradiation times of different treatment sites were obtained.The average irradiation dose was compared with the irradiation dose of the tumor target area.The ROC curve was used to classify cutoff values for tumor volume and BED_(10),and multiple linear stepwise regression models were used to analyze factors influencing the cumulative dose.Results:The average exposure frequency,cumulative radiation dose(cGy),and cumulative radiation dose/target area radiation dose(%)of patients using 6D-skull(skull)tracking,x-sight(vertebral)tracking,synchronous breathing tracking,fiducial(gold standard)tracking,and x-sight lung tracking were 131 times,1.6 cGy,0.02%–0.18%;212 times,8.0 cGy,0.05%–0.45%;322 times,12.2 cGy,0.06%–0.62%;237 times,10.1 cGy,0.07%–0.36%;and 411 times,12 cGy,0.20%–0.21%,respectively.The average exposure frequency,cumulative radiation dose(cGy),and cumulative radiation dose/target area radiation dose(%)of patients with brain,chest,abdomen,and pelvic tumors were 131 times,1.6 cGy,and 0.02%–0.18%;258 times,9.6 cGy,0.05%–0.62%;191 times,7.7 cGy,0.08%–0.44%;and 209 times,8.5 cGy,0.07%–0.36%,respectively.The ROC curve was classified according to tumor volume(cutoff value 30 mL)and BED_(10)(cutoff value 60 Gy).Moreover,the cumulative radiation dose was influenced by the BED_(10)target area volume,target area volume,and tumor site.The cumulative dose was higher when tumor volume was≥30 mL,BED_(10)>60 Gy,and tumors were located in the chest,abdomen,or pelvic cavity.Conclusions:The 6D-skull tracking method provided the lowest average exposure frequency and cumulative radiation dose for patients with brain tumors.The average exposure frequency and cumulative radiation dose were similar for patients with chest,abdomen,and pelvic tumors corresponding to the other four image guidance methods.Hence,the Cyberknife M6 stereotactic radiotherapy system can verify the real-time position accuracy of patients during treatment,and the radiation dose received by patients through this system is relatively low.