Room: Exhibit Hall | Forum 5
Purpose: Stereotactic body radiotherapy (SBRT) with IMRT for spinal tumor has been performed in recent years. Image guidance using cone-beam computed tomography (CBCT) has an important role for spine SBRT because the target is very close to or overlaps the organ at risk. However, the precision of CBCT registration may decrease based on the metal artifact of spinal fixation. In this study, the phantom mimicking vertebral bones with fixation metal implant was developed. Subsequently, the phantom was used to verify the influence of the metal artifact on the accuracy of image registration.
Methods: To mimic the actual condition of the patient, we used the vertebral bones of pigs, and two titanium bars were used as implants for spinal fixation. Epoxy resin that had a similar CT number to soft tissue was filled and congealed around the vertebral bones and titanium bars. In this phantom, the titanium bars can replace the acrylic bars to mimic the condition of no spinal fixation. CT and CBCT images were acquired after the titanium or acrylic bars were inserted in the phantom, and those were subsequently aligned by each three radiological technologists. The influence of the metal artifact on image registration accuracy was defined as the difference between the aligned positions in the conditions where titanium and acrylic bars were inserted.
Results: The measured registration difference was -0.03 to 0.07 mm, 0.01 to 0.18 mm, -0.03 to 0.07 mm, -0.12Â° to 0.00Â°, -0.02Â° to 0.07Â°, and -0.01Â° to 0.01Â° for LR, SI, AP, pitch, roll, and yaw, respectively.
Conclusion: The phantom that mimicked the condition of spine SBRT with spinal fixation was developed. The influence of the metal artifact on image registration accuracy was less.