First Retrospective QA of FAST-01 Clinical Treatment Fields Using High-Speed Quantitative Scintillation Imaging.

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Proton therapy requires precise dose and dose rate delivery for effective cancer treatment.
• The FAST-01 clinical trial utilizes proton beam scanning, necessitating accurate validation methods.
• Existing validation techniques may lack the spatiotemporal resolution required for complex proton fields.

Purpose of the Study:

• To retrospectively validate the delivered dose and dose rates in the FAST-01 clinical trial.
• To employ submillimeter spatial and sub-millisecond temporal resolution scintillation imaging for validation.
• To assess the accuracy of a novel imaging technique for proton therapy quality assurance.

Main Methods:

• An ultrafast intensified CMOS camera captured scintillation light from a scintillator sheet irradiated by proton pencil beam scanning fields.
• Camera calibration was performed using gafchromic film, and data was compared with EDGE diode detector measurements and log files.
• Dose and dose rate maps were generated from image stacks, with surface images projected to a 5 cm depth for further analysis.

Main Results:

• Camera response demonstrated high linearity with dose (R²=0.9998) and beam current (R²=0.9883).
• Gamma analysis (3%/2 mm) showed a 100% passing rate compared to film, indicating excellent agreement.
• Imaged dose rates at the surface and at 5 cm depth closely matched diode and log file data, with minimal deviations (1-2%).

Conclusions:

• This study presents the first independent validation of dose and dose rate for clinical proton FAST-01 fields with high spatiotemporal resolution.
• The developed scintillation imaging technique provides unprecedented 2D dose rate mapping capabilities.
• Direct 2D dose rate mapping is crucial for future pretreatment plan quality assurance in pencil beam scanning proton therapy.