J. Javor1,2, C. J. Tsai3, B. J. Cummings3, A. Mesci4, P. Wong2, V. C. Kong3, B. A. Millar5, L. A. Dawson3, R. K. Wong3, K. Del poso-Lee2, A. H. Safavi1, D. J. Valmonte6, S. Mheid3, T. Tadic7, and E. Taylor6; 1University of Toronto, Toronto, ON, Canada, 2Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, 3Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, 4Princess Margaret Cancer Centre, University Health Network, University of Toronto, Toronto, ON, Canada, 5Department of Radiation Oncology, University of Toronto, Toronto, ON, Canada, 6Princess Margaret Cancer Centre, Toronto, ON, Canada, 7Department of Radiation Oncology, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada
Purpose/Objective(s):Single-fraction stereotactic body radiotherapy (SBRT) for bone metastases results in better pain relief compared to conventional multi-fraction radiotherapy.However, the interval between simulation scan and commencement of SBRT can span from days to weeks.The aim of this studyis to assess the feasibility and efficiency of a simulation-free single-fraction SBRT for non-spine bone metastases by utilizing patient’s recent diagnostic CT (dCT) scans in place of CT simulation fortreatment planning. Materials/
Methods: The study is structured into two phases: 1) the development and validation of preclinical planning workflow, and 2) the application of the workflow for prospective delivery of simulation-free single-fraction SBRT. For the preclinical planning phase, simulation CT scans of patients who had completed palliative radiotherapy for non-spine bone metastases were imported and fused using translation-based shifts alone to mimic cone-beam CTs (CBCTs). Clinical Target Volumes (CTVs) were contoured and isotropically expanded to 10mm to generate Planning Target Volumes (PTVs). Plans were then created on the dCT and target coverage and organ-at-risk (OAR) doses were evaluated. Each plan had standard in-house physics quality control checks performed. Pre-clinical process development involved creating IGRT workflows, treatment and planning protocols. Radiation therapist and physicist education sessions were conducted. Actual target volume coverage and OAR doses were retrospectively compared with planned metrics using dose accumulation and compared using descriptive analyses. Results: For the first phase, 18 preclinical plans were created retrospectively utilizing patient’s dCT to four non-spine bone sites (pelvis (n=3), hip/upper femur (n=7), sternum (n=5) and scapula (n=3)) planned for 12-20 Gy in 1 fraction. Using standard IGRT thresholds for rotations based on bone-matched CBCT, simulated treatment PTV D95% and CTV D99% were within 6% (range: -6% to 2%; mean: -1%) and 4% (range: -4% to 4.1%; mean: 0%) of planned values, respectively. For the second phase, 4 patientshave been treated clinically thus far (sternum (n = 1), scapula (n=1), extremities (n=2)).Using CBCT-based dose reconstruction, PTV D95% and CTV D99% were within 8% (range -7.1% to -1.8%; mean: -3%) and 5% (range: -5% to 3.6%; mean: -1%) of planned values, respectively.Maximum dose to critical organs-at-risk was not significantly different compared with planned dose and tolerance was not exceeded.Average in-room time was 39 minutes (range: 30-57 minutes). Conclusion: Utilizing dCT for high dose single fraction palliative bone metastases patients is feasible and efficient.Future work includes collecting patient reported outcomes, patient and staff satisfaction with this new process and expanding on body regions included.
