Main Session
Sep
29
PQA 05 - Physics
Presenter(s)
Zhiheng Wang, PhD - University of Texas MD Anderson Cancer Center, Houston, TX
Z. Wang1, J. Yang1, M. C. Tom2, T. Salzillo1, Y. Ding1, T. M. Briere1, D. Mackin1, E. D. Subashi1, J. Wang1, A. J. Ghia2, and D. N. Yeboa2; 1Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, 2Department of CNS Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX
Purpose/Objective(s):
MR-LINAC Based Spine Stereotactic Radiosurgery (SSRS) has the advantages of seeing spinal cord during treatment delivery and using cine MR images for motion management. In this study, we developed workflow and gating parameters for MR-LINAC based spine stereotactic radiosurgery with cine MR images being used for real-time tracking. The workflow and gating parameters were validated with volunteer studies and applied for patient treatments.Materials/Methods:
A Unity MR-LINAC (MRL) with a comprehensive motion management (CMM) package was used for this study. A Klarity system was used for immobilization. Monaco planning system was used for treatment planning. All volunteer and patient studies were enrolled in IRB-approved protocols. One patient was treated with this workflow so far. During the MRL simulation, 3D T1-weighted and 3D T2-weighted MR images were acquired for treatment planning and cine images were acquired to evaluate the organ motions. Three gating structures, CMM_reg, CMM_target, and CMM_envelope, were created from CTV and its expansions. A reference plan was created in the Monaco planning system. RadCalc was used for second MU check. ArcCheck was used for IMRT QA. On the treatment day, a new set of 3D T2 weighted MR images was acquired, and the treatment plan was re-optimized with the adapt-to-shape (ATS) technique using the new images. A sagittal slice going through the spinal cord and target and a coronal slice going through the centroid of CMM_reg were used for real-time tracking during treatment delivery. For the occasions that the patient drifted out of the gating range, a baseline shift adaptive plan was created and a new tracking session was used to continue with the beam delivery.Results:
For the patient treated with MRL, 11 beams were used for IMRT planning. Similar clinical goals were achieved for both reference plan and adaptive plans with GTV coverage more than 95%, GTV minimal dose more than 15 Gy, spinal cord 0.01 cc dose less than 12 Gy, and spinal cord 1 cc dose less than 10 Gy. ArcCheck IMRT QA measurement passed with 99.1% passing rate for both reference and adaptive plans. A gating threshold of 1 mm for CMM VOICE achieves an optimal balance between the localization accuracy and the gating duty cycle. The duty cycle for the patient treated was 59.5%. The total time was 23.6 minutes.Conclusion:
Cine images acquired with MR-LINAC can be used for real-time tracking during MR-LINAC based spine stereotactic radiosurgery. A gating accuracy of 1 mm is achievable.