PET/CT worth extra radiation for those with high risk of lung cancer

While combination PET/CT imaging is one of the best ways to detect lung cancer, some are concerned about patient dose when using the modality on a large scale. However, researchers from Singapore optimized a low-dose PET scan while maintaining reliable cancer detection, according to a study published in the Journal of Nuclear Medicine.

Low-dose CT has supplanted x-ray as the modality of choice for cancer screening, but CT is by no means perfect. With a false positive rate of 96 percent, there’s clear room for improvement. 

“Specificity is poor, and the additional information from PET has the potential to improve [the scan’s] accuracy,” wrote lead author Joshua D. Schaefferkoetter of the University of Singapore and his colleagues. “If PET is to become a screening tool for patients at risk, however, the dose should be kept as low as practically possible. Investigative efforts must focus on defining the lowest reliable limits of PET.”

Researchers scanned 20 patients using a thresholding approach, finding uptake of the PET tracer was relatively stable until the “true count” (a measure of PET resolution) was decreased to one million. However, for human exam readers, performance was optimized around 10 million true counts. 

This is equivalent to a patient undergoing a PET scan for around 20 minutes resulting in an effective patient dose of 0.4 millisieverts—nearly half of the yearly dose limit for the general public. That may sound high, but for people with a high risk of lung cancer such as heavy smokers, the improved resolution provided by PET outweighs the risk posed by the additional radiation.