Halving radiation dose of whole-body CT trauma scans using single-bolus protocol
Whole body “pan-CT” enables rapid, potentially life-saving diagnoses of trauma patients, but with the tradeoff of high radiation dose exposure. The use of a split-bolus single-pass CT protocol can reduce radiation dose by nearly half compared to conventional two phase protocols.
But does it provide sufficient enhancement? British radiologists conducted a retrospective study published in the October issue of Clinical Radiology that showed it does. They evaluated 151 trauma CT examinations performed during a 5-month period of men over the age of 18 admitted to the emergency department of Royal Stoke University Hospital in Stoke-on-Trent. The majority of patients had been injured in accidents or by falling from heights or down flights of stairs. Seventy-three patients had the two-phase protocol and 78 patients the split-bolus protocol, with the choice of protocol selected by the radiologist in attendance at the time. All of the exams were performed using the same CT scanner.
The objective of the study was to determine if a split-bolus protocol achieved sufficient vascular enhancement while reducing patient dose. The researchers also recorded the rate of vascular and solid-organ injury to assess the benefit of reduced radiation exposure risk compared to the risk of not detecting occult injury.
The protocols
Lead author Vincent Leung, MD, and colleagues used a split-bolus protocol that provides both arterial and venous enhancement with a single pass of the CT gantry using a contrast medium injection. The injection consists of an initial slow injection (65 ml at 2 ml/s) providing solid-organ portovenous enhancement followed 10 seconds later by a second bolus (85 ml at 3.5 ml/s) giving angiographic enhancement. A 30 ml saline flush at 3.5 ml/s completed the procedure.
The conventional two-phase protocol included a bolus-tracking arterial phase acquisition from lung apices to the pubic symphysis triggered at 100 HU in the descending aortal, followed by a manually triggered venous phase from the diaphragm to the pubic symphysis acquired 50 seconds after completion of the arterial acquisition. The contrast medium injection was 100 ml at a rate of 4 ml/s, followed by a saline flush of 50 ml at a rate of 4 ml/s.
Findings and benefits
The two-phase protocol produced significantly higher arterial enhancement and significantly lower radiodensity measurements for the portal vein than the split bolus protocol. The split-bolus protocol had a significantly lower dose length product (420.8 mGycm) than the two-phase protocol (744.6 mGycm), with a mean DLP reduction of 43.5%.The radiologists stated that another benefit of the split-bolus protocol was that only a single series of images needed to be reviewed, reducing reporting time.
Although 14% of the patients sustained a solid and/or vascular injury that did require two-phase imaging, the majority – 86% - did not. And because the radiation dose of the split-bolus protocol was reduced by half, the authors stated that did not feel that the need for an additional CT scan for any such patient who had had the split bolus protocol would be significantly greater than if they had had the two-phase protocol.
In fact, the radiology department converted to 100% use of the split-bolus protocol by the end of the study in May 2014. In 2013 and at the beginning of the study in January 2014, no split-bolus protocols had been used.
REFERENCE
- Leung V, Sastry A, Woo TD, et al. Implementation of a split-bolus single-pass CT protocol at a UK major trauma centre to reduce excess radiation dose in trauma pan-CT. 2015 Clin Radiol.