Simulation-Free Single-Fraction High-Dose Radiotherapy for Non-Spine Bone and Soft Tissue Metastases

We evaluated the feasibility, efficiency, and dosimetric accuracy of a simulation-free, diagnostic CT (dCT)-based workflow for single-fraction radiotherapy to non-spine bone and soft tissue metastases.

This study included a retrospective preclinical validation phase and a prospective clinical implementation phase. Single-fraction plans (8-20 Gy) were generated directly from diagnostic CTs acquired ≤4 weeks prior using 3DCRT, IMRT, or VMAT, with geometric and dosimetric accuracy assessed by CBCT-based dose reconstruction prior to clinical implementation of simulation-free treatment. Feasibility outcomes included plan deliverability, treatment timing, CBCT utilization, and need for simulation. Dosimetric accuracy and acute toxicities were evaluated using dose-of-the-day analysis and chart review.

We generated 18 plans in the preclinical validation phase to demonstrate acceptable geometric and dosimetric agreement between dCT- and CBCT-based delivery. In the implementation phase, 29 patients were treated to 37 bone and soft tissue sites between December 2023 and March 2025. The median single-fraction dose was 10 Gy (range, 6-20 Gy). N=11 lesions (30%) received a single fraction of 12-20Gy stereotactic radiotherapy and 28 lesions (76 %) were treated with IMRT/VMAT. Mean CBCT-to-treatment time was 16 minutes versus 6 minutes for standard simulation-based workflows; simulation was required in two cases. Mean delivered dose deviations were -1.4% for CTV D99% and -3.4% for PTV D95%, no grade ≥3 acute toxicities were observed. Rotational setup error was the primary predictor of reduced target coverage.

Simulation-free, dCT-based single-fraction radiotherapy is feasible and safe for selected non-spine palliative indications, reducing hospital visits and enabling same-day treatment.