Characterization of MOSFET Dosimeter Angular Response Using a Spherical Phantom for Fluoroscopic Dosimetry.

Area of Science:

• Medical Physics
• Radiological Dosimetry
• Biomedical Engineering

Background:

• Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) dosimeters are standard for organ dosimetry in medical X-ray imaging.
• Fluoroscopy and cardiac catheterization involve variable X-ray projection angles, potentially affecting detector accuracy.
• Accurate dosimetry is critical for patient safety during complex interventional procedures.

Purpose of the Study:

• To characterize the angular response of MOSFET dosimeters under fluoroscopic irradiation conditions.
• To evaluate dosimeter performance at various angles relevant to pediatric cardiac catheterization.
• To establish angular correction factors for improved X-ray dosimetry in fluoroscopy.

Main Methods:

• Simulated biplane fluoroscopy beam quality using a biological X-ray irradiator.
• Fabricated a custom acrylic spherical scatter phantom for 3D angular response measurement.
• Measured MOSFET dosimeter response (mV) at 30° increments on axial and normal-to-axial axes and four common oblique angles.

Main Results:

• Axial rotation showed isotropic response (within ±10% deviation).
• Normal-to-axial rotation was largely isotropic, except at ψ = 270° (83 ± 9% relative response).
• Oblique angles showed minimal deviation: 102 ± 3% (90° LAO), 90 ± 3% (70° LAO/20° Cranial), 92 ± 3% (20° LAO/15° Cranial), 95 ± 3% (30° RAO).

Conclusions:

• MOSFET dosimeters exhibit predictable angular responses relevant to fluoroscopic procedures.
• Established angular correction factors will enhance dosimetry accuracy in pediatric cardiac catheterization.
• The spherical phantom is a versatile tool for comprehensive 3D dosimeter angular response characterization.