Comparison of computed tomography dose index in polymethyl methacrylate and nylon dosimetry phantoms

Abstract

The use of computed tomography (CT) scanning has been growing steadily. Therefore, CT dose measurement is becoming increasingly important for patient protection and optimization. A phantom is an important tool for dose measurement. This paper focuses on the evaluation of a CT dosimetry phantom made from nylon, instead of the standard polymethyl methacrylate (PMMA), which is not readily available or is too expensive in some countries. Comparison between phantoms made from the two materials is made in terms of measurements of the CT dose indices (CTDI). These were measured for four different beam widths and kVp settings at the center and periphery in head and body phantoms made from both materials and weighted CTDIs (CTDIw) were calculated. CT numbers along the z-axis of the phantom were also measured at the center and four peripheral positions of each scanned slice to check phantom homogeneity. Results showed that values for the CTDIw measured in the nylon phantoms were slightly higher than those from the PMMA while CT numbers for nylon were lower than those of PMMA. This is because the mass attenuation coefficient of the nylon is higher. Nylon could be used as a substitute material for CT dosimetry phantom to enable measurements and adjustment factors are given which could be used to estimate PMMA values for making comparisons with displayed values.

Development of a head CT dose index (CTDI) phantom based on polyester resin and methyl ethyl ketone peroxide (MEKP): a preliminary study

“…This material reduced the production cost to about one-fifth of that of the standard PMMA phantom. The results demonstrated that the CT number of the nylon phantom was 20 HU lower than that of the standard PMMA phantom [20], yet the findings of this study have provided convincing results.…”

“…Hence, the differences in CT number measured between the polyester resin and the standard PMMA phantom were less than 10 HU. This indicated that the polyester resin is more suitable than nylon as an alternative phantom [20].…”

“…Thus, efforts to find an alternative cheaper material with similar results to the standard PMMA phantom are essential. An alternative material for the phantom has been developed previously [20]. Sookpeng et al used nylon as a material for head and body phantoms for CTDI measurements, and reported that the values of CT number are about 20 HU lower than those of the standard PMMA phantom [20].…”

“…An alternative material for the phantom has been developed previously [20]. Sookpeng et al used nylon as a material for head and body phantoms for CTDI measurements, and reported that the values of CT number are about 20 HU lower than those of the standard PMMA phantom [20]. In addition, nylon also reduced production costs to about one-fifth compared to the PMMA phantom [20].…”

Simulação Monte Carlo do processo de aquisição de imagens de um tomógrafo de dupla energia

“…The HUs were obtained for both 80 and 140 kV spectra, and for the number of histories of 10 9 and 10 10 . Sookpeng et al (Sookpeng et al, 2016). In this case, the authors found CT numbers for nylon from 60 HU to 117 HU for different phantom sizes and energies.…”