[Study of Stability and Sensitivity of Three-dimensional Diode Array Detector].

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Intensity modulated radiation therapy (IMRT) is a standard cancer treatment.
• Patient-specific quality assurance (QA) is crucial for safe and effective IMRT delivery.
• The ArcCHECK (AC) 3D diode array is a common QA device.

Purpose of the Study:

• To evaluate the stability and sensitivity of the ArcCHECK (AC) 3D diode array.
• To assess the impact of positional errors on QA measurements.
• To determine the rate of sensitivity change in the AC diode array over time.

Main Methods:

• Positional accuracy tests were conducted on the AC array with lateral, longitudinal, and rotational displacements (0.5-3.0 mm/°).
• Sensitivity changes were monitored over 230 days using consistent calibration data.
• Volumetric-modulated arc therapy (VMAT) benchmark tests were analyzed using the gamma method (2 mm/2% criteria).

Main Results:

• Gamma pass rates significantly decreased with increasing positional errors.
• A 0.5 mm or 0.5° positional error led to pass rate reductions of 1.0% (lateral), 2.5% (longitudinal), and 4.2% (rotational).
• The AC array showed a sensitivity decrease of 2.2% per 100 days, impacting gamma pass rates.

Conclusions:

• The ArcCHECK (AC) 3D diode array exhibits high sensitivity to positional uncertainties.
• The sensitivity of the AC array degrades over time, necessitating recalibration.
• Regular array calibration is vital to maintain the accuracy of IMRT QA measurements.