Effect of the introduction of helical CT on radiation dose in the investigation of pulmonary embolism

Abstract

The aim of this study was to assess the change in patient radiation dose in the radiological investigation of pulmonary embolism since the introduction of helical CT pulmonary angiography (CTPA) in a large teaching hospital. All radiological investigations performed as an integral part of the imaging protocol in the investigation of clinically suspected pulmonary embolism (PE) were retrospectively reviewed. The protocol for the investigation of PE changed in our institution after the introduction of CTPA. Protocols 1 and 2 were the protocols in place before and after the introduction of CTPA, respectively. An in-depth evaluation was made of the imaging records and radiation dose for 30 consecutive patients investigated for clinically suspected PE in 1995 (protocol 1) and 2002 (protocol 2). Radiation doses were then extrapolated for the total number of patients investigated in each year. The number of radiological investigations performed per patient decreased from a mean of 1.17 in protocol 1 to 1.06 in protocol 2. There was a 44% increase in the total number of patients investigated. The effective dose per patient increased from 1.30 mSv to 1.35 mSv with the introduction of CTPA into the imaging protocol, an increase of only 4%. First line investigations showed a significant decrease in indeterminate examinations from 25.7% to 8.5%. Two different imaging protocols are reviewed with respect to type and number of procedures required for the investigation of PE and the resulting patient effective dose incurred. Results demonstrate an increase in the number of patients being investigated for suspected PE and a small increase in effective dose per patient since the introduction of helical CTPA. Although CTPA in itself incurs a higher effective dose, this is offset by the significant decrease in the number of non-diagnostic and total number of investigations per patient. In addition the ventilation component of lung scintigraphy was not required in protocol 2, thus reducing the dose further. We believe this small increase in effective dose is justified by the decrease in non-diagnostic studies and the reduction in total number of investigations per patient. We hope this paper will serve as a stimulus for the radiology community to examine current protocols in all areas of diagnostic imaging. We stress the importance of assessing new and established imaging investigative protocols to maximize the benefit and reduce any risk to patients.

How I diagnose acute pulmonary embolism

“…[31][32][33] Concerning acute PE, an alternative to CTPA is ventilationperfusion (V-Q) lung scintigraphy, which involves the simultaneous scintigraphic imaging of the pulmonary arteries and airways, with exposure to a radiation dose of 1.2 mSv. 34,35 A normal V-Q scintigram, one with no perfusion defects, virtually rules out PE with a 3-month failure rate of 0.9% (upper 95% CI, 2.3%). 35,36 A V-Q scintigram showing at least 1 segmental perfusion defect combined with a normal ventilation scan, the so-called highprobability lung scan, has a 85% to 90% predictive value for PE.…”

Cardiac CT for acute chest pain in the emergency department: advantages of prospective triggering

“…unpublished data, 2005; [26]). Other studies have quoted effective doses for a CT pulmonary embolism study to be *13.0-40.0 mSv [23,[27][28][29][30], particularly when taking into account the combined CT pulmonary angiography and CT venography study, with an average effective dose of 15 mSv based on a survey of the literature by Mettler et al [22,23]. In contrast, the effective radiation dose for diagnostic percutaneous coronary angiography ranges from 2.0 to 22.7 mSv with a typical dose of 2-7 mSv, and for stress-rest scintigraphy 9.4-40.7 mSv, depending on the protocol used, with doses in the higher range if thallium is used for any portion of the study [23,31,32].…”

A guide to foetal dose minimisation in computed tomography pulmonary angiography of the pregnant patient

“…5 One signifi cant aspect of multislice CT is the potential increase in patient, and hence foetal, radiation dose, due to the lower eff ective pitch used. 19 Using a 16-slice CT scanner Doshi, et al 4 measured a foetal radiation dose level for CTPA of up to 230 μGy. Th is proved to be comparable to the current VQ results.…”

“…One additional consideration in the CTPA versus VQ debate for foetal radiation dose stems from the fact that up to 60% of VQ examinations are indeterminate and require further investigations to confi rm a diagnosis. 19 Th is usually results in a CTPA scan being performed at a later date, delivering extra radiation to the foetus.…”