The recent safety investigation by the FDA of “radiation overexposures during perfusion computed tomography (CT) imaging to aid in the diagnosis and treatment of stroke” highlights the importance of carefully evaluating protocols for all CT procedures relative to both radiation dose and image quality.
The process of establishing a set of scan acquisition parameters (generally referred to as a scan ‘protocol’) has become much more demanding in recent years because the available options have greatly expanded, and various CT scanner manufacturers have adopted slightly different implementations. Ideally, each CT scan protocol would be designed to just meet the image quality need for the examination to be conducted on each patient, using the appropriate dose level. The lead radiologist, lead CT technologist, and qualified medical physicist should optimally converge to design and review all new or modified protocol settings, with the goal to ensure that both image quality and radiation dose aspects are appropriate. Additionally, a regular review process should be implemented to consider all protocols on a recurring basis to be sure that no unintended changes have been inadvertently applied that may degrade image quality or unreasonably increase dose.
Due to the complexity of modern CT scanners, there is a plethora of parameter setting combinations possible on each scanner model. The specific set to be used for any single exam is up to the supervising physician to determine. As a general guideline, the ACR has established dose reference levels for three common exams (adult brain, adult abdomen, and pediatric abdomen). Establishing CT dose reference levels for other less common exams, such as the head CT perfusion exam at the core of this recent overexposure incident, is much more difficult due to the nature of those specialty exams and the needs of individual patients.
It is likely that the recent incident of radiation overexposure from CT will promote more attention and resources to be allocated to appropriate CT protocol design, and that generally accepted ranges for radiation dose will eventually be developed for more types of CT examinations. (The ACR’s Dose Index Registry, currently under development for CT, is one such effort that will enable facilities to compare their CT dose indices against national benchmarks for all examinations and help to identify such incidents.) Such guidelines will be very helpful for all CT facilities and would also result in less variability among CT scan results obtained across the nation.
Finally, understanding the increasingly complex nature of CT scanner technology calls for more education on the part of imaging staff. Maintaining CT-specific continuing education is obviously critical to ensuring patient safety. In addition, obtaining ACR accreditation in CT provides an independent check of a facility’s personnel, imaging techniques, image quality and dose. The accreditation process also serves to generally increase the awareness of radiation dose within the facility and to ensure that the CT parameters used are appropriate.
Actions to Minimize Patient Dose in CT
- Together, the lead radiologist, lead CT technologist, and qualified medical physicist should design and review all new or modified protocol settings, to insure that both image quality and radiation dose aspects are appropriate.
- Develop internal radiation dose thresholds during any new CT protocol design.
- If an estimated dose value is above the applicable threshold for any routine clinical CT exam, implement steps to insure patient safety and reduce future risk.
- Institute a regular review process of all protocols to be sure that no unintended changes have been applied that may degrade image quality or unreasonably increase dose.
- Do not disable the CT dose estimate interface option; be sure that the dose information is displayed during the exam prescription phase.
- CT staff should maintain CT-specific continuing education that focuses on patient safety.
- Obtain ACR CT Accreditation for an independent check of a facility’s personnel, imaging techniques, image quality and dose.
See the FDA’s alert.
More information on the ACR's diagnostic reference levels in medical x-ray imaging
More information abut the ACR's CT Accreditation program
For more information abut the ACR's Dose Index Registry.