ASNC: Techs play lead role in PET, CT dose reduction

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DENVER—As important players within the medical community work to reduce unnecessary radiation exposure from medical imaging, integrating protocols and strategies, such as shielding, can help reduce dose, James A. Case, PhD, of Cardiovascular Imaging Technologies in Kansas City, said during a presentation Sept. 9 at the 16th annual American Society of Nuclear Cardiology (ASNC) meeting.

Case, a director of physics at the practice, outlined safety considerations for PET and CT as well as methods to reduce dose for both patients and technologists. “If you [the technologist] think your role in radiation safety is minor, think again,” Case said.

In fact, Case reverted back to the CardioGen-82 (Bracco) recall, which he said resulted in a $40 million loss and thousands of patients needing to have their PET and SPECT imaging rescheduled simply because sites failed to perform adequate quality control.

Failing to perform quality control on a regular basis is problematic and has the potential to result in penalties. In fact, failure to perform quality control may soon result in civil and criminal punishment, Case offered.

Case urged technologists to follow quality control as described by manufacturers, as this can help thwart these hardships. He added that all staff must be trained on radiation safety and that practices must be able to produce records of radiation use to inspectors.

While Case noted that the aforementioned strategies are critical to lowering radiation exposure and improving care, during the presentation he also outlined various myths within the nuclear cardiology field, such as whether a lower dose is equal to a lower quality.

Imaging exams with lower doses, such as Rb-82 studies or N-13 ammonia studies have even better imaging quality compared to previous studies performed at higher doses of radiation. In fact,  these studies are performed with only 3.3 mSv and 1.7 mSv, respectively.

“Low dose does not equal low quality,” Case said. “It is merely based on how you choose the protocol and how you choose the instrumentation.”

Does a lower radiation dose equal lower efficiency? This too is a myth, Case noted. In fact, dual isotope studies can be performed in 90 minutes or less while stress tests, which also emit lower radiation, can be completed in less than 50 minutes. “Therefore, studies with lower radiations actually benefit workflow and enhance lab efficiency.”

Case compared the radiation risk to the risk of dying from cardiac death, noting that while a coronary CTA exposes patients to 15 mSv per scan and mortality is 15,000/million patients, there is no radiation risk associated with cardiovascular disease (CVD), however, the risk of dying of CVD is much higher—19,000 per one million patients.

“The killer here is not radiation,” Case offered, “it's cardiovascular disease.”

Alongside reducing patient radiation dose, technologists must also look for ways to minimize worker radiation exposure during CT and PET scans. With SPECT, it will be important to look at distance and dosage, while during CT it will be imperative to look at shielding, distance and time. “CT systems have a lot of dosage being emitted but shielding can be a very effective tactic,” Case said. “Stay out of the room during scanning.”

Other ways to minimize patient exposure include: limiting mAs, using appropriate kVps, minimizing slice overlapping and varying tube currents. Additionally, Case said that each imaging study should undergo a risk-benefit model to determine dosage. Attenuation correction during PET and SPECT and calcium screening during CTA angiography is also important.

The most important protocol however, is the use of ECG-pulsed spiral scanning. With this method, tube current can be reduced by up to 80 percent during the systolic phase with up to a 50 percent dose reduction possible. “If your scanner does not have this capability, it is probably not as good of a technology as you think for cardiac imaging."

As for CT, Case said that increasing the pitch can help decrease dose as compared to adding mAs and kVps, which both increase dose.

He added that quality control procedures for the Rb-82 generator will be an “absolutely critical step.” Staff should allow the sample to stand for at least one hour and the activity of the sample should be measured. Additionally, using more filtering can also increase quality. Therefore, filter settings should be set to lower cutoff frequencies (10 percent for gated and non-gated).