Dose and slice thickness evaluation with nMAG gel dosimeters in computed tomography

Area of Science:

• Medical Physics
• Radiological Physics
• Imaging Science

Background:

• Computed tomography (CT) is crucial for clinical diagnosis, necessitating accurate radiation dose estimation and image quality assurance.
• Ensuring patient safety and diagnostic accuracy in CT imaging relies on precise measurement of radiation dose and image parameters.
• Multi-detector CT (MDCT) systems require robust quality assurance protocols to maintain diagnostic efficacy and minimize radiation exposure.

Purpose of the Study:

• To evaluate the efficacy of nMAG gel dosimeters for simultaneous measurement of the 300-mm weighted CT dose index (CTDI) and slice sensitivity profile (SSP) in MDCT.
• To establish R₂–dose response curves using MRI for nMAG gel dosimeters at different tube voltages (120 and 140 kVp).
• To assess the accuracy of nMAG gel dosimeters by comparing their measurements with conventional methods like ionization chambers and radiochromic films.

Main Methods:

• nMAG gel dosimeters were employed to measure CTDI (CTDI₁₀₀ and CTDI₃₀₀) and SSP within home-made cylindrical phantoms.
• Magnetic resonance imaging (MRI) was utilized to analyze the irradiated gel and generate R₂–dose response curves.
• The full width at half maximum (FWHM) of the SSP was measured for various slice thicknesses and compared to radiochromic film results.

Main Results:

• The difference in weighted CTDI₁₀₀ between the gel dosimeter and ionization chamber was less than 1%.
• CTDI efficiency at 120 and 140 kVp ranged from 80.1% to 82.5%.
• The FWHM of the SSP measured by the gel dosimeter closely matched the nominal slice thicknesses, validating its accuracy.

Conclusions:

• nMAG gel dosimeters, when used with custom phantoms, provide accurate 300-mm weighted CTDI and slice thickness information for MDCT.
• This dosimetry system demonstrates significant potential for routine quality assurance in MDCT imaging.
• The findings support the integration of nMAG gel dosimetry into clinical practice for enhanced CT quality control and patient safety.