Dosimetric evaluation of a 320 detector row CT scanner unit

Abstract

BackgroundThe technologic improvements in Multislice scanners include the increment in the X-ray beam width. Some new CT scanners are equipped with a 320 detector row which allows a longitudinal coverage of 160 mm and a total of 640 slices for a single rotation. When such parameters are used the length of the traditional pencil chamber (10 cm) is no more appropriate to measure the standard weighted computed tomography dose index (CTDIw) value.Materials and methods.Dosimetric measurements were performed on a 640 slices Toshiba Aquilion One CT scanner using common instrumentation available in Medical Physics Departments.ResultsFor the measurements in air, two different ionization chambers were completely exposed to the beam. Dosimeters showed an acceptable agreement in the measurements. To evaluate the actual shape of the dose profile strips of Gafchromic XRQA film were used. Films were previously calibrated on site. From the graphic response of the scanned film it is possible to evaluate the full width at half maximum (FWHM) of the dose profile which represent the actual beam width.ConclusionsComputed Tomography Dose Index (CTDI) and Dose Length Product (DLP) need to be changed when the beam width of the CT scanner is over 100 mm. To perform dose evaluation with the conventional instrumentation, two parameters should be considered: the average absorbed dose and the actual beam width. To measure the average absorbed dose, the conventional ionization chamber can be used. For the measurement of the width of the dose profile, Gafchromic XRQA film seemed to be suitable.

Does body mass index outperform body weight as a surrogate parameter in the calculation of size-specific dose estimates in adult body CT?

“…CTDI vol is calculated based on a 10-cm pencil chamber and therefore SSDEs might not be applicable on these scanners. 20 In conclusion, a good correlation between body weight and effective diameter as well as BMI and effective diameter in adult chest and abdominal CT examinations was shown in the presented study. BMI demonstrated a significantly better correlation with D eff for abdominal CT, whereas weight showed a significantly better correlation in chest CT. On average, SSDE value per patient calculated with one of the two surrogate parameters for abdominal and chest CT, respectively, differed ,6% from those calculated with the reference standard.…”

Estimation of primary radiation output for wide‐beam computed tomography scanner

“…5 Because the _ K 0Àw=oÀA and _ K 0ÀwÀA indicate only the primary radiation output detected by the ionization chamber, the dose gradient along the zaxis is not accommodated. 5 Because the _ K 0Àw=oÀA and _ K 0ÀwÀA indicate only the primary radiation output detected by the ionization chamber, the dose gradient along the zaxis is not accommodated.…”

“…2,5 Because these measurements are carried out with little scattered radiation, they are utilized not only for the determination of _ K air , but also for characterization of the half-value layer (HVL) 6,7 and the bow tie filter profile. 2,5 Because these measurements are carried out with little scattered radiation, they are utilized not only for the determination of _ K air , but also for characterization of the half-value layer (HVL) 6,7 and the bow tie filter profile.…”

Application of a color scanner for 60Co high dose rate brachytherapy dosimetry with ebt radiochromic film

“…Radiation dosimetry is essential for quality assurance in diagnostic and therapeutic radiology 1,2. One of the most frequent tools for dosimetry are radiochromic films (RCF) because (1) they have nearly a tissue equivalent base material, (2) their spatial resolution is high, (3) they have a minor energy and dose rate dependency, and (4) they do not require a darkroom and developing 3–5.…”