Intravenous iodinated contrast used during chest CT exams has been shown to increase DNA damage from radiation, according to a study recently published in the Journal Radiology in early February. “Because of X-ray exposure, the risk of developing cancer is increased as a result of additional DNA damage, primarily in the form of DNA double-strand breaks,” wrote the study’s authors.

Risks from iodinated contrast agents have been well-studied previously, they noted. But these were considered to be mostly in the form of kidney damage and cytotoxic — the impact on DNA was little understood. To determine its effects, the researchers zeroed in on the development of doublestrand breaks in DNA in those who underwent chest CT scans.

For the study, 245 patients (96 women and 149 men) were recruited from December 2009 to October 2011. Of the total, 66 underwent CT with no contrast. The other 179 had exams with contrast material — an intravenous administration of an average of 18.651 mg of iodine per patient.

To determine possible DNA damage, the average number of phosphorylated histone HSAZ (yH2AX) foci lymphocyte was followed with fluorescence microscopy. CT scans elevated yH2AX foci levels in both contrast and non-contrast groups but for those who had been given contrast the levels rose by a significantly larger amount, approximately 107 percent, a sign of increased DNA radiation damage.

Their findings, wrote the researchers, imply two salient points: that the dose-length product with CT does not properly measure the potential risk of X-ray radiation damage unless contrast’s impact is taken into account. This is of particular import when exams are repeated, during follow-up, for example, suggesting the use of iodinated contrast agents should be weighed even more carefully.

HCBN went to editorial advisory board member and professor of radiology at University of Pennsylvania, Abass Alavi, to get his thoughts on the report. Alavi is a pioneer in molecular imaging and one of the key individuals behind the introduction of F18-Fluorodeoxyglucose (FDG) for use with positron emission tomography.

“Over the past two decades, it’s become increasingly apparent that contrast agents may not add more information than what we can gain these days from non-enhanced FDG-PET/CT. The information provided by administering contrast agents is very limited in nature and only relates to the vasculature of the lesion which is proven to reveal indirect evidence for disease activity” Alavi says.

“So the need for contrast enhancement may disappear if we combine either CT or MR with PET which is becoming the powerhouse in medical imaging. By adopting this approach, you are combining the benefits of structural imaging without contrast with those of imaging at molecular-cellular level. You’re using PET with FDG which is quite safe and the balance radiation-wise is not substantially different (but lower) from that delivered from CT with contrast enhancement.

However, the significant risks associated with iodinated contrasted agents are eliminated. There is really no single report that describes that FDG itself has caused any side effect in the millions of people who have received this diagnostic agent. The body doesn’t recognize this preparation as a true drug, it’s just a spy that goes inside our body and lets us to get to the information we need to properly manage our patients,” he says.

According to Alavi, it’s not just the risk of a relatively rare but serious problem, like an anaphylactic reaction, or significant renal damage. The real risk comes with not having the needed level of sensitivity and specificity with CT or MR alone to manage serious diseases like cancer and heart disease effectively. The latter according to Alavi stands as a counter to the cost-versus-benefit argument of the use of standalone contrast-enhanced CT rather than PET/CT or PET/MR in the near future. “It turns out CT costs maybe half to one-third the cost of PET, but in reality, the story changes,” he says, “When you look at the impact of standalone contrast-enhanced CT versus FDG-PET in disease outcome.” The low sensitivity and specificity of CT and or MR result in under-over treating of many serious diseases which results in enormous suffering of affected patients and significant costs to the health care system.

For an example, if the cancer has already spread to the lymph nodes or the other sites in the body, but based on CT findings that indicate the disease is confined to the primary site an operation is performed on that assumption, then six months and $100k later, the cancer appears at the spots that were missed by CT on the original scan. It is horrible for the patient to go through this surgery and then end up with a disaster that could have been avoided by performing PET imaging at the outset.

Furthermore, CT is non-specific and about 20 to 30 percent of the lesions visualized are false positive finding and as such should be left alone. The non-specificity of CT can lead to more tests and sometimes surgeries/treatments which increase the potential for needless suffering and even death.”