In vivo dosimetry for estimation of effective doses in multislice CT coronary angiography

Abstract

In vivo dosimetry represents a technique that has been widely employed to evaluate the dose to the patient mainly in radiotherapy. Considering the increment in dose to the population due to new high-dose multislice CT examinations, such as coronary angiography, it is becoming important to more accurately know the dose to the patient. The desire to know patient dose extends even to radiological examinations. Thermoluminescent dosimeters are considered the gold standard for in vivo dosimetry, but their use is time consuming. A rapid, less labor-intensive method has been developed to perform in vivo dosimetry using radiochromic film positioned next to the patient's skin. Multislice CT scanners allow the estimation of the effective dose to the patient from the dose length product (DLP) parameter, the value of which is displayed on the acquisition console, simply multiplying the DLP by published conversion factors. The method represents only an approximation based on standard size circular phantoms and neglects the actual size of the patient. More accurate evaluations can be carried out using software-based Monte Carlo simulations. However, these methods do not consider possible dose reduction techniques, such as automatic tube-current modulation. For 22 patients effective doses measured by in vivo dosimetry and calculated by software were compared. The technique of using in vivo dosimetry measured with radiochromic film appears a promising procedure for improving the assessment of the effective dose to the patient.

An investigation into factors affecting the precision of CT radiation dose profile width measurements using radiochromic films

“…The primary reason was that the relationship between the optical density of the film and dose is nonlinear in the relevant dose range. 18 In addition, our investigation indicated that narrower beam width was more sensitive to the film calibration (R 2 = 0.68 and 0.85 for FWHM and FWTM, respectively). It is worth noting that, in the subsequent routine measurement of FWHM and FWTM, all the scan parameters should be kept the same from year to year so as not to introduce unnecessary systemic variations.…”

“…23 Previous studies have recommended to conduct film calibration using single channel (usually red) only. 6,18 The reason was that the maximum absorption of Gafchromic films is typically seen at red wavelength. However, single channel dosimetry is very sensitive to background nonuniformity caused by film thickness variation and artifacts caused by document scanners.…”

“…The XR-QA2 films operate in a wide dose range from 1 to 200 mGy. 18 Its effect on the FWHM and FWTM measurements was assessed by measuring the beam widths in the permissible range of the tube current-time product: 50, 100, 200, 300, and 400 mA s. In this experiment, the kVp was held constant at 80 kVp so as to vary only one parameter at a time.…”

Dosimetric evaluation of a 320 detector row CT scanner unit

“…A calibration curve specific for the CT scanner beam quality was then obtained and it was used to convert the pixel values of the film into dose values (Figure 1). 7…”

Abdominal Pediatric Cancer Surveillance Using Serial Computed Tomography: Evaluation of Organ Absorbed Dose and Effective Dose

“…The detailed analysis of ED in this study allowed the assessment of the relationship between dose length product (DLP) and ED 9,10,11,12,13 . The dose length product (DLP) was estimated using the volume computed tomography dose index (CTDI vol ) and the CT scan length 14 .…”