Doctors use cesium chloride salt, which contains the cesium-137, to blood before it is given to patients in blood transfusions. The radiation is aimed at preventing transfusion associated graft-versus-host disease (TA-GVHD), a rare but nearly always fatal complication to blood transfusions, in which transfused white blood cells attack the recipient’s tissue.  This treatment helps to save lives, and in the United States alone, 500 blood irradiators irradiated almost 2 million blood units in 2013. 
Unfortunately, cesium chloride salt also poses significant health and security risks if misused by accident or by an intentional act of terrorism. The material is highly dispersible (like talcum powder), soluble in water, highly radioactive and binds easily to surfaces like concrete. Additionally, the cesium-137 in cesium chloride salt has a half-life of 30 years, meaning it will stay around for a long time and pose a serious danger if inappropriately handled. If terrorists or other non-state actors acquire the material, it can be employed in a radiological dispersal device or RDD (one type of RDD triggered with conventional explosives is commonly known as a “”). Weapons employing cesium chloride salt could kill or injure people directly exposed to the material, contaminate large areas for a long time, cause widespread panic and require very expensive decontamination efforts. Therefore, use of cesium-137 in cesium chloride salt for blood irradiation is a double-edged sword. On the one hand it can be used to help save lives, but on the other hand it could be used to do widespread harm. Phasing out the use of cesium-137 in favor of non-radioactive alternatives, while still maintaining the capability to help patients who need access to irradiated blood, would do much to eliminate this dilemma.
There have been several global incidents involving various forms of cesium-137, illustrating the serious safety and security risks of this radioactive isotope. In Goiana, Brazil, four people died and hundreds were hospitalized after a capsule containing cesium-137 ruptured, resulting in one of the worst radiological disasters in history. The source was not a blood irradiator, but the incident highlights the risk this isotope poses. Mass contamination resulted in the demolition of many buildings, and roughly 112,000 people sought medical attention out of fear they might have been exposed to radiation, overwhelming the healthcare system, and preventing people who needed other medical attention from receiving it.
One way to counter the risk that cesium-137 sources could be misused would be to secure all locations where the material is used, such as hospitals and research centers. However, ongoing security expenses could be considerable, and securing blood irradiators still in medical use would not necessarily prevent their long-term improper disposal. Many of the worst accidents involving radioactive materials like cesium-137, including the Goiana incident, occurred because a source was abandoned or improperly disposed of in a scrapyard. So, heightened security would serve to reduce the threat but it would not permanently eliminate it.
A better solution would be to substitute non-radioactive materials for cesium-137, which are capable of providing the same societal benefits without significant safety or security risks. In blood irradiation, there are alternatives that do not require the use of radioactive materials. These alternative technologies include x-ray technologies, linear accelerators (LINACs) and dedicated photochemical (“UV”) sterilizers. However, such alternative technologies have been slow to be adopted in the United States. According to a 2008 survey conducted by the American Association of Physicists in Medicine (AAPM), 85% of U.S. respondents used cesium-137 irradiators, 9% used x-ray tube containing devices and 6% used LINACs (none used “UV” sterilizers because at the time of the survey the technique had not yet been approved by the U.S. Food and Drug Administration).  A 2016 survey of 34 doctors conducted by the National Institutes of Health found that more than half were willing to switch immediately to, or at least test, alternative technologies, but the remainder were unwilling to switch to alternative technologies. 
Blood irradiation occurs predominantly in the more advanced medical systems of high-income countries, but several of these countries have been curtailing the use of cesium chloride blood irradiators to reduce the risk that the materials could be misused. France and Denmark have banned the use of cesium-137 sources for blood irradiation, Sweden and Finland strongly encourage the use of x-ray tube containing technology and Japan only allows the use of x-ray technology. Norway stated at the 2016 that since 2015 it has successfully converted all of its blood irradiators to x-ray technology.  Not only does this replacement x-ray technology provide the same blood sterilizing medical benefits as did the cesium chloride blood irradiators, it also eliminates the risk the machines’ materials could be intentionally or inadvertently misused.
The United States has been slower to respond to the threat posed by cesium chloride blood irradiators. However, the U.S. federal government has evolved in its thinking about the urgency of the problem. After the National Academy of Sciences published a report on the feasibility of replacing high-risk radioactive sources with non-isotopic alternatives, an interagency Task Force on Radiation Source Protection and Security was formed and issued reports in 2010 and 2014.  While the 2010 report was circumspect about conversion, the 2014 report established an Interagency Working Group on alternatives coordinated by the Department of Energy.
In 2014, the Department of Energy started the Cesium Irradiator Replacement Program (CIRP), which gives end-users of cesium-137 irradiators a financial incentive to exchange them with x-ray irradiators. X-ray irradiators have been approved by the FDA since 2005, but are not in wide use in the United States.  At the 2016 Nuclear Security Summit, the U.S. government pledged to partner with industry to replace 34 cesium-137 blood irradiators with alternative technologies by 2020, a task that has already started with several conversions in New York and Atlanta.  Top California policymakers, including Gov. Jerry Brown and Sen. Dianne Feinstein, have urged hospitals and blood banks in their state and nationwide to consider conversion.  However, more work needs to be done to engage with policymakers and industry on the threat and to educate them about effective alternative technologies; hundreds of cesium-137 blood irradiators still remain in place today in the United States – and globally—many of which are not slated for near-term replacement.
 Michael D. O'Hara, Ph.D., FDA/CDRH/OIVD/DRAD, Radiological Devices Advisory Panel Meeting, April 12, 2012, www.fda.gov.
 Department of Health and Human Services, "The 2013 AABB Blood Collection, Utilization, and Patient Blood Management Survey Report," 2015, 63, www.aabb.org.
 Gerald A. White, Jr., to Michael Lesar, FAAPM, October 15, 2008, Subject: Request for Comments on the Security and Continued Use of Cesium-137 Chloride Sources and Notice of Public Meeting, www.aapm.org.
 Interagency Working Group on Alternatives to High-Activity Radioactive Sources, "Transitioning from High-Activity Radioactive Sources to Non-Radioisotopic (Alternative) Technologies," Office of Science and Technology Policy, December 2016, pp. 21, 35, https://obamawhitehouse.archives.gov.
 Prime Minister Erna Soldberg, National Statement: Norway, Nuclear Security Summit, Washington, D.C., April 1, 2016, www.nss2016.org.
 Radiation Source Protection and Security Task Force, "The 2010 Radiation Source Protection and Security Task Force Report," August 11, 2010. Radiation Source Protection and Security Task Force, "the 2014 Radiation Source Protection and Security Task Force Report," August 14, 2014, www.nrc.gov.
 C. Brogdon, Center for Devices and Radiological Health, to Ross Kachaniwsky, Director, Quality and Regulatory Affairs, May 26, 2005, Department of Health and Human Services, Food and Drug Administration, www.accessdata.fda.gov.
 Nuclear Threat Initiative, "Preventing a Dirty Bomb: Effective Alternative Technologies for Radiological Security," April 4, 2017, www.nti.org.
 Nuclear Threat Initiative, "NTI and State of California Partner to Reduce Radiological 'Dirty Bomb' Risks," May 3, 2017, www.nti.org.