Diagnostic Imaging for Vertebral Metastases (DIVERT): A Simulation-Free VMAT Pilot Patient Study
Abstract
Purpose
We assessed the dosimetric and workflow feasibility of using a previously acquired diagnostic CT (DICT) for palliative VMAT planning of vertebral metastases in a prospective pilot patient study.
Methods
Thirty patients were enrolled and a total of 43 disease sites along the thoracic, lumbar, and sacral spine were treated as part of this study. Patients followed the conventional radiotherapy pathway, though for treatment planning CT (TPCT) simulation were aligned to replicate their DICT positioning. Parallel treatment plans were created on both DICTs and TPCTs, following independent target contouring. At the time of treatment, patients were positioned using anatomic landmarks, with CBCT verification. Setup and treatment time were recorded. Offline, the DICT and TPCT scans were registered at the level of the target, and the plan created on the DICT was recalculated on the TPCT. Conventional dose-volume and segment comparison metrics were recorded to evaluate plan quality and contour similarity.
Results
Using the TPCT as ground truth and the registered DICT as a surrogate for patient alignment on the treatment couch, recalculating the DICT on the TPCT led to TPCT PTV coverage of, on average, V95% > 97%, and D95% > 97% of the prescription dose. On average, target volume D2% did not exceed 108% of the prescription dose. The mean±SD of the Dice Similarity Coefficient and Hausdorff Distance of registered DICT and TPCT CTVs was 0.86±0.08, and 2.1±1.4 mm, respectively. Most commonly, a single CBCT was acquired at the time of treatment, and average patient in-room time was within the standard twenty-minute booking slot for a single disease site.
Conclusion
This study demonstrates that DICT can be used for the planning and delivery of palliative VMAT radiotherapy to the spine without loss of target coverage or increase in OAR toxicity, omitting the need for a dedicated TPCT.