Technical note: Patient-specific quality assurance for multi-target single-isocenter SRS-A target-specific approach

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiosurgery

Background:

• Advancements in radiotherapy necessitate improved planning for multi-target intracranial stereotactic radiosurgery (SRS).
• Multi-target-single-isocenter (MTSI) planning enhances beam delivery precision and reduces treatment time.
• Current patient-specific quality assurance (PSQA) methods are often impractical for accommodating all targets in a single QA session.

Purpose of the Study:

• To develop and validate a novel PSQA approach for MTSI cases.
• To ensure precise dose coverage for individual targets or neighboring target groups (T-NTG) within MTSI plans.
• To adapt existing QA devices for comprehensive assessment of complex SRS plans.

Main Methods:

• Utilized a custom script to calculate T-NTG coordinates relative to the beam isocenter.
• Created individual QA verification plans for each T-NTG, repositioning the beam isocenter for precise alignment with the SRS MapCHECK (SRS MC).
• Performed gamma-index analysis (GIA) using CBCT images for SRS MC alignment and assessed passing rates (PR) for 75 QA plans using 6MV-FFF beams and Volumetric Modulated ARC Therapy (VMAT).

Main Results:

• Achieved a PR > 95.5% for all QA plans using the 1.0 mm/2.0% GIA criteria, with an average PR of 98.9%.
• 63% of plans achieved PR > 99.0%, and 92% achieved PR > 97.0%.
• Statistical analysis indicated that the PSQA method consistently approaches a 99% PR, demonstrating its reliability for targets, including those in the lateral dose-fall-off regions.

Conclusions:

• The proposed PSQA method, involving T-NTG relocation, is a reliable and clinically acceptable tool for MTSI SRS.
• This approach effectively addresses the limitations of single-session QA for complex multi-target SRS cases.
• The findings support the routine implementation of this PSQA strategy in radiation oncology departments.