锥形束CT在线调整大分割放射治疗椎体转移癌*

目的：评价锥形束 CT（CBCT）在线调整技术在大分割治疗椎体转移瘤中的应用价值。评价分次间摆位误差及治疗过程中靶区位移对治疗的影响。方法：2008 年12 月至 2009 年08 月，应用医科达 Synergy 系统治疗椎体转移瘤 10 例，每次照射前、调整后及治疗后获取 CBCT图像，将获取图像和计划 CT图像匹配，获得靶中心 X（左右）、Y（头脚）、Z（前后）方向的位移及旋转角度误差，分析误差及分布规律。应用逆向调强放射治疗技术，靶区剂量 63 Gy/9 次，隔日照射。随访 6 个月。结果：10 例患者共 10 个靶区 CBCT扫描 269 次。首次摆位在X、Y、Z 方向位移误差分别为（-0.90 ±4.20 ）mm、（-0.40 ±4.90 ）mm、（-2.50 ±3.40 ）mm，旋转角度误差分别为（-0.20 ±1.65 ）°、（-1.12 ±1.84 ）°、（0.22 ±1.48 ）°。调整后其位移误差分别为±0.80 mm、±0.90 mm、（-0.10 ±0.80 ）mm；治疗后分别为（-0.10 ±1.30 ）mm、±1.80 mm、（0.10 ±1.40 ）mm。调整后角度误差分别为（-0.21 ±1.06 ）°、（-0.72 ±0.96 ）°、（0.33 ±0.85 ）°；治疗后分别为（-0.15 +1.27 ）°、（-0.64 ±1.39 ）°、（0.62 ±1.18 ）°。调整前PTV 外扩值范围为8.40 ～11 .00 mm，调整后缩小为1.20 ～1.50 mm。10 例患者疼痛缓解，未发现放疗副作用。治疗 6 个月后复查骨扫描提示核素浓聚减少。结论：CBCT在线调整能纠正摆位误差，既满足靶区剂量的提升也有效降低了脊髓受量。高剂量大分割图像引导调强放疗技术是治疗椎体转移瘤的一种安全、有效的新方法。

Study of Hypo-Fractionated Image-Guided Intensity Modulated Radiotherapy (IG-IMRT) for Treating Spinal Metastasis Using Cone-Beam Computed Tomography (CBCT)

Objective:To evaluate the applicability and effectiveness of hypo-fractionated image-guided intensity modulated radiotherapy (IG-IMRT) in treating spinal metastasis and to investigate the interfractional and intrafractional radiotherapy setup errors for spinal metastasis using kV-CBCT.Methods:From October2008to August 2009, 10patients with spinal metastasis were treated with the Elekta Synergy TM system. All patients received kilovoltage cone beam computed tomography (kV-CBCT) before receiving radiation treatment, after correction and treatment. The acquired X-ray volumetric images (XVI) which were co-registered with planning CT and errors of isocenter position on left-right (LR) , superior-inferior (SI) and anterior-posterior (AP) axes X, Y, and Z and angle of rotation were obtained and analyzed. The dose prescribed to metastatic lesions was 63Gy/ 9f, with the mean spinal cord dose limited to < 34.2 Gy and per fraction dose < 3.8 Gy. Patients were followed up for6 months for pain relief and bone lesion resolution. Results:Ten patients were treated and received a total of 269 CBCT scans. Before set-up correction, the translational positioning errors (means ± SD) in the left-right (X), superior-inferior (Y) and anterior-posterior (Z) axes were (-0.90± 4.20), (- 0.40± 4.90) and (-2.50± 3.40) mm, respectively; the rotation errors were (- 0.20± 1.65), (- 1.12 ± 1.84) and ( 0.22±1.48) degrees, respectively. After correction, those errors were ( 0.00± 0.80), (0.00± 0.90), (- 0.10± 0.80) mm and (- 0.21± 1.06), (- 0.72± 0.96), (0.33± 0.85) degrees, respectively. The pre-correction PTV margins were from 8.40to 11.00 mm, while the post-correction margins were from 1.20mm to 1.50mm. All patients requested pain relief. After6 months, all patients were rechecked with a bone scan showing significantly decreased nuclide accumulation. There was no radiation-induced toxicity detected clinically during a median follow-up of 6 months. Conclusion:Measurement of setup error before radiation delivery using kV-CBCT scan combined with on-line correction greatly improves the patient setup precision and ensures the implementation of an optimal IMRT plan, satisfying both the dose escalation of tumor targets and the radiation tolerance for spinal cords. High-dose, hypo-fractionated IG-IMRT may provide a new therapeutic direction.