Abstract:
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.