CyberKnife beam output factor measurements: A multi-site and multi-detector study

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Accurate measurement of small field output factors (OFs) is critical for stereotactic radiosurgery.
• New detector technologies offer potential improvements for OF measurements.

Purpose of the Study:

• To conduct a multicenter evaluation of two new generation detectors for OF measurements on CyberKnife systems.
• To compare the performance of microDiamond and plastic scintillation detectors (PSDs) against corrected silicon diodes.

Main Methods:

• PTW-60019 microDiamond and W1 PSD were used to measure OFs on eight CyberKnife units (5-60mm cones).
• Measurements were compared to Monte Carlo (MC) corrected silicon diode data.
• PSD data were corrected for Čerenkov Light Ratio (CLR), with uncertainties estimated.

Main Results:

• Averaged over all centers, differences between MC-corrected diodes and the new detectors were within 1.5%.
• MicroDiamond showed a consistent over-response of 1.3% at 7.5mm and a 0.2% difference at 5mm.
• PSD slightly under-responded (<1%) for smaller cones, while CLR variability impacted OF values by 1.9%.

Conclusions:

• CyberKnife microDiamond OF measurements require corrections below 2%, demonstrating consistency across units.
• PSD shows good agreement with MC-corrected diodes, but CLR determination needs further investigation.
• Multicenter validation is valuable for assessing detector performance in clinical settings.