Cherenkov imaging for linac beam shape analysis as a remote electronic quality assessment verification tool

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Quality Assurance (QA) in radiation therapy is critical for patient safety.
• Accurate measurement of radiation beam shape is essential for effective treatment delivery.
• Traditional methods for beam verification can be time-consuming and labor-intensive.

Purpose of the Study:

• To evaluate a remote Cherenkov emission imaging system for quantitative measurement of linear accelerator (linac) beam shapes.
• To verify the system's capability for Quality Audit (QA) at the irradiation surface.
• To assess the system's potential for simplifying conventional QA procedures.

Main Methods:

• A Cherenkov camera captured 2D dose images on an ABS plastic phantom for various 6 MV photon beam sizes (5x5 cm² to 20x20 cm²).
• Measurements were performed at a source-to-surface distance (SSD) of 100 cm and compared with GaF film and linac light fields.
• Interreader comparisons and measurements on two different Clinac2100 machines were conducted.

Main Results:

• Cherenkov image widths closely matched GaF film and light field measurements within ±1 mm standard deviation.
• Discrepancies were within the tolerance of standard linac QA procedures.
• The system enabled quantitative extraction of radiation field shapes at the SSD.

Conclusions:

• The Cherenkov imaging system offers a valid method for remote radiation field size confirmation.
• It provides comparable information to traditional linac light fields or GaF film estimates.
• Automated analysis and potential for dynamic beamlet verification present significant advantages for future QA.