D. Wang1, H. Kim2, T. Zhuang2, J. Visak2, M. H. Lin2, B. Cai2, D. D. M. Parsons2, A. R. Godley2, and S. B. Jiang2; 1UT Southwestern Medical Center, Dallas, TX, 2Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX
Purpose/Objective(s): We investigate the feasibility of performing online adaptation and treatment for spine stereotactic ablative radiotherapy (SAbR) using X-ray-based adaptive radiation therapy (ART). We hypothesize this could potentially eliminate the necessity for patient-specific simulation CT and conventional treatment planning. The treatments can be possibly delivered on the same day of patients’ consultation. This is extremely beneficial for patients, often in excruciating pain, to avoid waiting for three to seven days in the conventional workflow. Materials/
Methods: To demonstrate the feasibility of our simulation CT omitted treatment strategy, we used a pre-clinical release version of Ethos Emulator 2.0 treatment planning system and ART emulator. In our study, the prescriptions were 14Gy in one fraction to the vertebral body with simultaneous integrated boost to 20Gy. The constraints for the spinal cord were maximum dose less than 14Gy and V10Gy<=0.35cc. Plans were normalized to 95% to a planning structure using 20Gy PTV subtracting spinal cord with 3mm expansion. All pre-plans were using the same 12 equally spaced IMRT beams and Ethos pre-planning template. Five thorax test patients with Hypersight CBCTs are selected for this study. A library patient with similar immobilization device and anatomy was searched and paired for each test patient. The simulation CTs of library patients were used for pre-planning in Ethos TPS. Ethos emulator 2.0 was used to generate online adaptive plan on the test patients’ CBCT using the pre-plans from the library patients. During the online ART, library patients PTVs were adjusted to match to actual test patients anatomy on CBCT. The PTV coverages and spinal cord doses were evaluated. Results: All five test patients meet PTV coverage goals and spinal cord dose constraints. The average PTV V20Gy = 93.6% (90.2-95.2%). The average PTV V14Gy = 93.1% (92.0-95.4%). All cord maximum doses are less than 14Gy and the V10Gy less than 0.35cc. The online adaptive plans and pre-plans present similar dosimetric metrics. The average difference in the coverage of PTV 20Gy and PTV 14Gy are 0.88% (0.1-3.1%) and 1.38% (0.2-3.8%), respectively. The average difference in spinal cord dosimetry are: 0.43Gy (0.09-0.61Gy) for maximum dose and 0.02cc (0-0.05cc) for V10Gy. Conclusion: This study lays the groundwork for future investigations on feasibility of treating spine SAbR patients without needing simulation CT. The online adaptive plans generated through our workflow achieved similar quality as the preplan of the library patients. This study provides and demonstrates the feasibility of an efficient yet reliable and reproducible strategy to treat spine SAbR patients. This strategy is achieved by online ART using library patients’ simulation CTs, thus omitting the CT simulation for actual patients.
