Concerns over radiation dose levels pose threat to CT's future growth

The most important limiting factor for CT in the future is patient radiation dose, and radiologists must consider how to minimize dosage levels, according to Prof. Matthias Prokop of Utrecht University Medical Centre in the Netherlands.

"Dose is our number one enemy, especially as more advanced scanners are introduced," he said during Saturday's special focus session. "It may be reduced by adhering to proper clinical indications and decreasing the size of the exposed region. If correct procedures are followed, dose in multislice CT does not need to be greater than in conventional CT."

The downside of thinner sections is more noise unless dose is increased, but the critical question is determining the noise levels that can be tolerated.

"The honest answer to this question is that we don't really know, but I suspect it's probably more than we think," he said.

Noise can be reduced by reconstructing thick sections (axial/multiplanar reconstruction) and using different reconstruction kernels. New techniques for dose containment, such as improved detector electronics, dose modulation, and adaptive filtering, should also be considered.

Medical procedures account for more than 20% of total radiation received by an average population, said Dr. Keith Harding, an adviser in radiation safety to the European Commission and International Commission on Radiation Protection. Special care must be taken with CT and interventional radiology. The media are paying increasing attention to this issue.

"A photo of a man with a large radiation burn that required skin grafts recently appeared on the Internet. He had had two angioplasties and one angiogram. Such cases are not unique," he said.

Failing to diagnose serious conditions can be expensive, and Harding presented figures based on actual data obtained from the U.K. courts. A missed cerebral abscess may lead to compensation for the patient worth £272,000 (about 370,000 euros), while failing to spot a slipped femoral epiphysis can cost a doctor £131,000. The comparable figure for cervical cancer is £154,000, for cancer of the larynx £5000, and for a prolapsed vertebral disc £500.

Fear of litigation should not lead to the indiscriminate and uncontrolled use of x-ray, however, Harding said. A skull x-ray is not recommended for chronic headache or epilepsy, for instance.

The possibility of litigation due to radiation exposure is lower if a radiology department operates within the relevant imaging referral guidelines, said Prof. Adrian Dixon, head of radiology at the Addenbrookes Hospital in Cambrige, U.K.

Dixon also discussed breast cancer litigation, albeit not for exposure but for missed and/or delayed diagnoses. He estimates that a fifth of all medical litigation in the U.K. concerns breast cancer screening.

"Radiologists are reluctant to go into this area because it is increasingly seen as a minefield. It sometimes feels like you will be sued if you screen and sued if you don't screen," he said.

This raises the question whether women at risk should be offered ultrasound or MRI, which improve mammography's sensitivity and specificity.

Dixon advocates the use of MRI as a follow-up technique for patients with lymphoma or testicular tumors. Other areas that must be looked at closely are hematuria and acute abdominal pain.