Tissue Reactions in Cardiologists and Cardiology Patients
There are two main biological effects of radiation: stochastic effects, which include carcinogenetic and genetic effects, and tissue reactions (previously called deterministic effects), which cause an immediate and very predictable change to the tissue. Tissue reactions happen when the dose exceeds a specific threshold. The two most frequent examples of tissue reactions (deterministic effects) of cardiological interest are cataract formation (in doctors) and skin injury (in patients).
Cataract, or opacification of the lens, is often associated with visual impairment and may be classified into three main categories: nuclear, cortical, and posterior subcapsular, according to their anatomic location. Of the three major categories of age-related cataracts, posterior subcapsular is the least common but it is the one most frequently associated with ionizing radiation exposure. Because of their location along the lens' visual axis, relatively minor posterior subcapsular cataracts can have great impact on vision. The estimated eye dose is around 0.5 mGy/procedure, in cardiac catheterization laboratories when no eye protection is used. Until recently, the dose threshold for radiation-induced lens opacities were considered 2 Gy for a single dose or 5 Gy for fractionated dose. However, several epidemiological studies among Chernobyl clean-up workers, A-bomb survivors, astronauts, residents of contaminated buildings, and surveys of staff in interventional rooms indicate that there is an increased incidence of lens opacities at doses below 0.5 Gy and even suggests a stochastic hypothesis (non-threshold effect). Whether deterministic or stochastic in nature, lens opacities have been documented in up to 50% of interventional cardiologists. The reasons for this high prevalence are three fold: first is that operator's eyes are exposed to scattered x-rays; second (avoidable) is the frequent failure of some cardiologists to use protective leaded eyewear; and probably third, that the permitted occupational dose limits were too high even to provoke a mental alert. On April 21, 2011, ICRP slashed the earlier dose limit of 150 mSv in a year for the lens of the eye to the present 20 mSv in a year, averaged over a defined period of five years, with no single year exceeding 50 mSv.
When fluoroscopic procedures require more than 20 minutes using high-contrast fluoroscopy mode or 60 minutes in low level fluoroscopy, there may be a possibility of patient skin injuries. Significantly, injuries are not limited solely to the use of older equipment, but can occur when poor technique is employed with newer and digital equipment capable of delivering higher doses. Radiation burns remain asymptomatic and often go unrecognized. This is quite contrary to the familiar thermal burn, which is associated with a recognizable source of heat and instantaneous pain. They usually occur on the patient's back (where the x-rays are delivered) and since they develop several weeks after the procedure their association with cardiac interventions may not be considered, and many severe cases come to light through litigation. A case is filed in US courts every 4–5 weeks by patients who have suffered such injuries. In almost every country around the world, reporting significant radiological incidents and accidents that occur during, or as a direct result of using ionizing radiation for a medical procedure is a legal requirement. But in practice, such reporting hardly ever occurs. Very few countries have a functioning reporting system because no one wants to be blamed for patients' radiation related burns, hair loss or skin injury. However, this information is essential if lessons are to be learned. The IAEA has set up its own international reporting system called SAFRAD (SAFety in RADiological procedures). Because the SAFRAD system is anonymous and the IAEA will not supply identifiable data to governmental authorities or other third parties, there will be no fear of blame.