Room: Exhibit Hall
Purpose: Recent advances in volumetric and planar image guidance and patient immobilization have led to an increase in use of spine SRS. Challenges in this region include the need for accurate dosimetric calculations in bone/tissue/lung interfaces and the optimization of deliverable plans with sufficiently sharp dose gradients to spare the spinal cord, particularly in cases where disease extends to the pedicles and transverse processes. BrainLab Elements uses a split PTV optimization which uses multiple arcs to target different regions of the target individually, minimizing difficulties due to desired concavities in the desired dose distribution.
Methods: Patient data sets selected for treatment plan creation include three patients who were planned to single vertebral body lesions. For these patients, the prescription dose was set to 16, 20, and 24 Gy to 95% of the target volume to assess the ability to meet constraints with dose escalation. Parameters for plan evaluation included conformity index (CI), gradient index (GI), homogeneity index (HI), and maximum point dose to the spinal cord. Two VMAT arcs were used for treatment planning.
Results: The maximum spinal cord point dose was 13.1, 13.9, and 14.2 Gy for 16, 20, and 24 Gy prescriptions respectively in the Elements plans. CI was constant across prescriptions at 1.1, and GI was 3.4, 3.3, and 3.3 respectively. GI was also relatively unaffected by prescription dose, remaining at 1.2. Target coverage suffered slightly to maintain cord sparing at 24 Gy, falling to 93.6% at 24 Gy.
Conclusion: The treatment of spine lesions in a single fraction up to 24 Gy is possible using the Brain Elements treatment planning system. Future work includes comparing these plans to those created in other planning systems and the dosimetric validation of the delivery.
Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by a grant from BrainLab.