Type:
Educational Exhibit
Keywords:
Radioprotection / Radiation dose, Radiation physics, Radiographers, CT-Angiography, CT, Dosimetry, Radiation safety, Dosimetric comparison
Authors:
M. Kato1, K. Chida2, T. Moritake3, F. Sasaki4, T. Oomura4, N. Takahashi5, H. Oosaka4, H. Toyoshima4, T. Kinoshita4; 1Akita, Akita/JP, 2Sendai/JP, 3Kitakyusyu/JP, 4Akita/JP, 5Akita, Japan/JP
DOI:
10.1594/ecr2018/C-0406
Background
Coronary computed tomography angiography (CCTA) is widely used for noninvasive cardiac imaging to evaluate coronary artery disease (Fig.1).
As CCTA examination delivers higher radiation doses compared to other types of computed tomography (CT) examinations,
it is crucial to manage the radiation exposure.
High radiation doses have the potential to cause deterministic effects and stochastic effects in patients.
Furthermore,
according to ICRP Publication 105,
the tissue weighting factor,
which is a relative measure of the risk of stochastic effect,
for the breast was increased from 0.05 to 0.12 in order to assess the carcinogenic risk effectively.
Characteristics of the dosage index value of CT
Recently,
CCTA is increasingly being adopted for the pre-operative examination and post-operative assessment of percutaneous coronary intervention (PCI).
However,
various CT protocols do not provide procedures to evaluate the patient’s entrance dose.
Although CT dose index (CTDIW) and dose length product (DLP) are provided as the radiation dose structure report,
they do not take the patient's body weight into consideration and do not have a clinically direct relation to the patient’s exposure dose.
The CTDIW represents the average absorbed dose at a point on a patient’s body undergoing CT scan.
It is measured using a 10-cm long CT chamber and a cylindrical polymethylmethacrylate phantom (Fig.2).
The DLP is calculated as the product of the CTDIvol and scan length (in centimeters).
The DLP does not represent the volumetric dose,
but has a relatively strong association with the effective dose.