Amid a campaign of terror that has included beheadings and suicide bombings, recent reports from the Middle East that Islamic State extremists may now have stolen enough material for a radioactive "dirty bomb" are chilling — but should not be shocking.

This new threat originates overseas, but the potential for disaster posed by dangerous radiological materials here at home is just as serious. Radiological materials used in medical equipment and scientific research are at risk. Concerns have been brewing for years because the very same isotopes that can make lifesaving blood transfusions and cancer treatments possible — such as cesium-137, cobalt-60 and iridium-192 — could be used to build a bomb that would spread radioactive material and contaminate significant portions of a major U.S. city. We are exposed, and the clock is ticking.

Unlike a nuclear weapon, a radioactive dirty bomb would not cause catastrophic levels of death and injury, but depending on its chemistry, form and location, it could leave billions of dollars in damage due to the costs of evacuation, relocation and cleanup — and the inevitable follow-on threats could have severe economic and psychological repercussions. Buildings would likely have to be demolished and the debris removed. Access to a contaminated area could be denied for years as a site is cleaned well enough to meet even minimum environmental guidelines for protecting the public.

The materials that could be used to wreak such havoc are dispersed across thousands of sites in more than 100 countries, and many of them are poorly secured. Concerns about the Islamic State are a powerful reminder of what's at stake — and should provide impetus for governments, the medical community and industry globally to immediately secure all such materials or replace them with alternative technologies.

At home, there are a number of steps we should put on the front burner:

• First, although securing the materials is crucial, a better option exists for some isotopes that would result in permanent threat reduction. Thanks to recent technological advances, it is no longer necessary to use one of the most dangerous materials, cesium-137, in medical and scientific equipment. Cesium-based blood irradiators at hospitals can and should be replaced with technologies approved by the U.S. Food and Drug Administration that don't use radiological material but that achieve equivalent medical outcomes. All hospitals should replace these irradiators to reduce their risks and potential liability if their dangerous materials harm others. This risk reduction is a high-priority national security matter, and governments should render appropriate assistance when required.

• Second, liability and insurance gaps must be carefully reviewed by those possessing and responsible for the security of radiological sources. A hospital, for instance, could be financially devastated if required to pay huge damages in the wake of a dirty-bomb attack using its materials, unless the hospital specifically has insurance that covers such losses. Hospital officials should evaluate their current coverage; they likely will find that eliminating their radioactive sources is more cost-efficient than paying high premiums for expanded coverage and funding proper security. In addition, publicly traded companies that use radiological sources should provide more specific information about the associated risks in response to Securities and Exchange Commission disclosure and reporting obligations.

• Third, we need to strengthen the regulatory framework for the security of radiological sources. As noted in a 2012 Government Accountability Office report, security requirements put forth by the U.S. Nuclear Regulatory Commission (NRC) are too broadly written. The NRC should provide medical facilities with specific steps they must take to develop and sustain a more effective security program.

• Fourth, states should immediately be allowed to go beyond a federal minimum security standard if they choose. As it stands, even if a state wants to voluntarily increase security for its radiological sources beyond federal minimums, the NRC regulations don't allow it. State regulators' hands are tied because state regulations for the majority of U.S. radiological material essentially must be identical to those established by the NRC. One size does not fit all, however. New York City has a higher risk profile than Kansas City, Mo., or New Orleans.

• Finally, the international community should do more. Last year, 23 countries at the Nuclear Security Summit agreed to secure their most dangerous radioactive materials. Other countries should join this pledge. Next year's summit offers governments a valuable opportunity to announce their fulfilled commitments and launch a major new initiative to replace all cesium blood irradiators and other dangerous radiological sources where alternatives exist.

Given the stated interest by terrorist groups and the widespread availability of potentially dangerous radiological sources, it is nothing short of a miracle that we have not yet seen a dirty-bomb terrorist attack. We must act before our luck runs out.

Sam Nunn is co-chairman of the Nuclear Threat Initiative (NTI) and a former Democratic senator from Georgia. Andrew Bieniawski is vice president for material security and minimization at the NTI. They wrote this article for the Washington Post.