PubMed · 14088008
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
N T WINKLER. 1963. A PRACTICAL WATER PHANTOM.. https://pubmed.ncbi.nlm.nih.gov/14088008/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
PURPOSE: To evaluate effects of varying tube current and voltage on radiation dose, image noise, and image contrast with different phantom sizes and shapes. MATERIALS AND METHODS: Four round lucite phantoms with 8-32-cm diameters were scanned with multi-detector row computed tomography (CT) and 80-120 kVp. Radiation dose was based on CT dose index, image noise, and iodine contrast and measured with constant and variable tube currents that were age appropriate for each tube voltage. Radiation dose and image noise and contrast were compared in round and oval 24-cm phantoms. For various combinations of technical factors and phantom sizes and shapes, percentage differences were calculated for radiation dose and image noise and contrast. Associations between tube voltage and radiation dose, image noise, and image contrast in round and oval phantoms were determined by fitting second-degree polynomials to data. Differences in radiation dose and image noise and contrast, which were attributable to differences in tube voltage, were tested with paired t tests. RESULTS: With 165-mAs tube current, radiation doses with 140- and 80-kVp tube voltages were 103% ([41.9 mGy - 20.6 mGy]/20.6 mGy) and 58% ([10.2 mGy - 4.2 mGy]/10.1 mGy) higher in the 8-cm phantom than in the 32-cm phantom. When tube current was adapted for phantom size, radiation dose at 80 kVp in the 8-cm phantom was reduced by 82% ([10.1 mGy - 1.8 mGy]/10.1 mGy). In the 8-cm phantom, tube voltage was decreased from 120 to 80 kVp and tube current remained at 165 mAs, resulting in a 68% noise increase ([3.1 HU - 1.8 HU]/1.8 HU). With variable tube current, 80-kVp tube voltage in the 8-cm phantom led to a 138% noise increase ([7.3 HU - 3.1 HU]/3.1 HU). With reduced tube voltage, image contrast increased. In the 8-cm phantom, with a constant 165-mAs tube current and a decrease in tube voltage from 120 to 80 kVp, there was a 35% ([333 HU - 217 HU]/333 HU) increase in contrast. No difference was noted in radiation dose or noise between round and oval phantoms (P = .604 and P = .06, respectively), but a small statistically significant difference (1%) in contrast attenuation was demonstrated (P = .025). CONCLUSION: Reduced tube voltage for pediatric contrast material-enhanced CT reduces radiation dose and maintains image contrast. Image noise increases, but the effect is minimal in smaller phantoms. An additional reduction in tube current further reduces radiation dose.
We report on an experimental examination of a new powerful optical source with potential application in radiotherapy treatment simulation. The illuminance, effective source position, and source size have been measured for this new source and, for comparison, for conventional sources on a simulator and a linear accelerator. This new source is considerably brighter than those in common use in radiotherapy. Its effective optical source size is larger than that on the linear accelerator tested but comparable with that on a conventional simulator.
It has been found that in general 10 MV X-ray dose calculation can be made accurately for multi-leaf collimator irregular fields by using the total scatter factor (S(cp)), collimator scatter factor (S(c)), and phantom scatter factor (S(p)) proposed by Khan et al. With respect to the collimator scatter factor (S(c)), we used the field-mapping method of Kim et al. to obtain equivalent square fields of irregular fields (the collimator reverse effect can be accurately dissolved using the field-mapping method). Even for extremely small multi-leaf fields compared with the main collimator opening, X-ray output calculations could be made accurately by introducing the small segment correction (SSC) factor. With respect to the phantom scatter factor (S(p)), highly accurate calculations could be made for irregular field irradiation by applying an F(MLC) (MLC radiation leakage) factor to the equivalent square field (in cases in which the ratio of the multi-leaf equivalent square field side to the main collimator equivalent square field side is less than 0.6). However, it has been found that highly accurate dose calculations can, in general, be performed when the main collimator is limited just at the opening determined by the multi-leaf collimator field.