Adaptive-driven CT simulation-free multi-fraction SBRT radiotherapy: Initial clinical experience.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Diagnostic CT for radiotherapy (RT) planning bypasses traditional CT simulation but poses challenges in patient positioning and Hounsfield unit (HU) fidelity, impacting dose accuracy.
• A Varian Ethos adaptive-driven CT direct-to-treatment (DtT) multi-fraction stereotactic body radiation therapy (SBRT) workflow is presented to address these challenges.

Purpose of the Study:

• To validate the accuracy of using diagnostic PET-CT images for Ethos treatment planning.
• To assess the feasibility and efficiency of an adaptive-driven DtT SBRT workflow using diagnostic PET-CT.
• To evaluate the performance of the Ethos system with Hypersight (HS) for HU and dosimetric accuracy compared to helical CT simulators.

Main Methods:

• Institutional diagnostic PET-CT images were used to create initial Ethos treatment plans.
• HU and dosimetric accuracy were validated across PET-CT, Ethos CBCT (with/without HS), and helical CT simulators.
• The workflow involved initial planning on diagnostic PET-CT, with the first fraction delivered using an adaptive plan on HS CBCT, which then served as the reference for subsequent fractions.

Main Results:

• The DtT adaptive SBRT workflow was successfully implemented and demonstrated feasibility.
• The Ethos system, particularly with HS, maintained HU fidelity and dose calculation accuracy comparable to helical CTs.
• On-table adaptive sessions averaged 37-51 minutes, and subsequent non-adaptive fractions were completed efficiently in 7-27 minutes.

Conclusions:

• Diagnostic PET-CT can be feasibly used for DtT adaptive-driven multi-fraction SBRT.
• This workflow reduces the need for pre-treatment patient presence and expands planning lead times.
• The approach enhances overall radiotherapy efficiency for selected patients.