Room: Exhibit Hall
Purpose: To assess dosimetric feasibility of spine stereotactic body radiotherapy (SBRT) of two different beam delivery systems for re-irradiation patients with metastases to more than two consecutive vertebrae.
Methods: Five patients were included in this planning study. Using the CyberKnife and Vero4DRT system, the following two plans with a total prescribed dose of 24 Gy in 2 fractions using three target dose objectives (D95, D50 and Dmax) were generated: Plan A (applied to first SBRT, and this was a control plan) with 17.0 Gy radiation volume irradiated to the PRV of the spinal cord (PRVcord) limited to 0.035 cm3 (D0.035cm3 â‰¤ 17.0 Gy) and Plan B (applied to re-irradiation cases, this was an experimental plan) with PRVcord D0.035cm3 â‰¤ 12.2 Gy. The constraints of PRVcord were stipulated as being strict. After planning, dose-volume histogram analysis was performed for all regions of interest.
Results: In all cases, the PRVcord D0.035cm3 met the dose constraint in all plans, although some differences in target dose coverage were observed between Plan A and B. Both modalities achieved acceptable target dose constraints in the Plans A, whereas, the Plans B with the Vero4DRT did not meet the dose objectives of Dmax for the two cases with the large target volumes. In the Plans B using the CyberKnife, D95 (mean Â± SD: 12.8 Â± 2.1 Gy) and Dmax (34.7 Â± 1.1 Gy) were not satisfied in all cases.
Conclusion: An isocentric linear accelerator with a MLC, such as Vero4DRT, is capable of static IMRT beam delivery for multiple spine SBRT in re-irradiation patients. However, the non-isocentric apparatuses using robotic arms might have some limitations for such patients due to the characteristics of the system. Regardless of the treatment apparatuses, the severity of tolerance dose of the spinal cord and tumor size can affect treatment plan quality.
Intensity Modulation, Treatment Planning, Treatment Techniques