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

Abstract

Computed tomography (CT) has been widely used in clinical diagnosis. It is important to estimate radiation dose and perform image quality assurance procedures for CT scans. In this study, nMAG gel dosimeters were used to simultaneously measure the 300-mm weighted CT dose index (CTDI) and slice sensitivity profile (SSP) for multiple detector CT (MDCT). Magnetic resonance imaging (MRI) was performed on the irradiated gel to create R2‒dose response curves for the tube voltages of 120 and 140 kVp. The gel dosimeters were loaded in three home-made cylindrical phantoms to obtain CTDI100 and CTDI300. The full width at half maximum (FWHM) for 2, 5, 10, 14.4, and 38.4-mm slice thicknesses was measured and compared with the result obtained by radiochromic films. The difference in weighted CTDI100 obtained by the gel dosimeter and ionization chamber was less than 1%. The CTDI efficiency at 120 and 140 kVp was in the range of 80.1%–82.5%. The FWHM of SSP measured by the gel dosimeter matched very well with the nominal slice thickness. The use of nMAG gel dosimeters combined with the home-made cylindrical phantoms can provide 300-mm weighted CTDI and slice thickness information, showing potential for quality assurance and clinical applications in MDCT.

The Impact of Temporal Changes in Irradiated nMAG Polymer Gels on Their Applicability in Small Field Dosimetry in Radiotherapy

“…It is important to note that this process is extremely fast when the solution is cooled down below 35 °C, but the evolution is much slower in later phases. This process can take up to 30 daysor longer and may cause shrinkage of the gel by losing water, which leads to the density changes in irradiated gels contributing to the evolution/instability in the dose responses [ 10 , 39 , 43 , 44 , 45 ]. Post-irradiation polymerization reactions progress up to 10 h after the irradiation [ 19 , 42 ], however, they do not fully stop due to the presence of remaining long-term radicals.…”

“…Radiation-sensitive polymer gels, whose response to irradiation is based on the radiation-induced polymerization of a monomer (and often co-monomer) species suspended in a gelatin matrix, have the potential to meet these limitations and can be used for the recording of dose profiles and the verification of complicated dose distributions in external beam therapy [ 6 ]. Various techniques, such as magnetic resonance imaging (MRI) [ 7 , 8 ], X-ray computed tomography (CT) [ 9 , 10 ], optical computed tomography (OCT) [ 9 , 10 , 11 , 12 , 13 ] or ultrasound [ 14 , 15 ] can be used for the evaluation of 3D dose distribution changes caused by the polymerization of irradiated polymer gels. Raman spectroscopy may also be considered as a power full tool for investigating radiation-induced changes in polymerized gel dosimeters, since the radiation-induced changes of the vibrational bands of corresponding monomers/polymers in gels correlate with the absorbed dose.…”

“…Both methods indicated an acceptable gamma passing rate (<1) since a voxel agreement of 95% for the target level was achieved between the treatment plan and gel-measured dose distributions, applying 3% dose and 3 mm distance-to-agreement gamma function criteria. Interesting results on the X-ray CT application for the dose response evaluation in polymer gel is provided in paper [ 10 ]. In this study, the nMAG gel dosimeter and the home-made cylindrical phantoms were used for the CT dose and image quality assurance.…”

Head CT dose reduction with organ‐based tube current modulation

“…This method is used as a quality assurance tool in radiation therapy, 23 and to measure slice thickness and CT dose index (CTDI) in CT scans 24–26 . However, since polymer gel dosimeters require MRI for reading, magnetic field inhomogeneities and temperature rise due to radiofrequency pulses may lead to uncertainty 27,28 . In recent years, a leuco crystal violet (LCV) dosimeter with low uncertainty has attracted attention 29,30 (Figure 2a).…”

“…[24][25][26] However, since polymer gel dosimeters require MRI for reading, magnetic field inhomogeneities and temperature rise due to radiofrequency pulses may lead to uncertainty. 27,28 In recent years, a leuco crystal violet (LCV) dosimeter with low uncertainty has attracted attention 29,30 (Figure 2a). We hypothesized that an LCV dosimeter could detect twiceirradiated areas in settings where the PF is < 1.0 and measure them.…”