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RADIATION EXPOSURE IN CATH LAB: HOW TO STAY SAFE?

The cardiac catheterization laboratory is such a place where ionizing radiation is much in use. In this closed atmosphere, the working staffs (i.e. cardiologists, cath lab technicians, nurses, trainees and other support staffs) are at potential risk to radiation exposure almost on a daily basis . Due to some factors, like – configuration of the X-ray equipment, number of cardiac cath cases per day and often long screening needed for the procedures contribute to the relatively high level of exposure to ionizing radiation compared to other such areas (e.g. radiology, urology, gastroenterology, some other operating rooms). Radiation in cath lab comes from two different sources: i) fluoroscopy and ii) cine angiography (cine). Fluoroscopy is used for catheter, guidewire, balloon, stent placement etc. and this mode involves about 95% of the total X-ray operation time, but only causes 40% of the total radiation exposure. Cine, on the other hand is used to acquire diagnostic images and to generate a permanent record of the procedure. Cine mode represents only 5% of the total X-ray tube operation time, but responsible for 60% of the total radiation exposure to staff and patients. It is important that the radiation doses acquired by the cath lab personnel are measured effectively. The International Commission on Radiological Protection (ICRP) recommends the use of effective dose (E) to evaluate the effects of partial exposure to ionizing radiation and relate this to the risk of equivalent whole body exposure. It is expressed in Sievert units (Sv)(1 Gray unit =0.7 Sv). The intensity of the biological effect of X-rays is dependent on the absorbed dose (total radiation energy per unit mass) of sensitive tissue and is expressed in gray units (Gy). The average dose per procedure for the cardiologist is estimated as 0.05mGy.

Potential Hazards of Radiation Exposure: These include: a) Injury to skin. Threshold for transient skin erythema is about 2 Gy. b) Radiation may also interact with and alter cellular DNA. Majority of these interactions are inconsequential since damage can be repaired. c) Damage to eye: Relatively high dose of radiation can damage conjunctiva, iris, sclera and blood vessels of retina. The lens however is the critical site, for it may sustain irreversible damage from a relatively low dose of radiation and subsequently formation of cataract. d) There is a small probability that the DNA damage will remain altered and can potentially cause cancer induction (carcinogenesis) and genetic defects. The incidence of these effects increases with the increasing radiation exposure. The incremental fatal cancer risk is estimated at 4% per Gy unit. Thus a 7.14 Gy unit exposure per year for 30 years will have an incremental risk of 0.6% in addition to 20-22% incidence of cancer in the general population. The organs that have the greatest risk of cancer formation are brain, skin and thyroid. The gonads however are at lower risk of developing cancer.

Methods of Reducing Radiation Exposure: Time: The lower the amount of time spent in a radiation area, the lower the exposure will be. Therefore every effort should be made by the operating cardiologist in the cath lab to minimize the fluoroscopy and cine screening time. Distance: Increasing the distance from the radiation beam decreases the risk of exposure. Doubling the distance between the primary beam and the operator, reduces the exposure by a factor of 4. In addition, the radiation exposure varies according to the angle at which the camera is projected. Oblique views and steep angulations increase radiation exposure (though often used to improve visualization). 60-degree angulation gives up to 3 times the operator dose than 30-degree angulations. Shielding: Lead shields and shielding will significantly reduce the risk of exposure but only if appropriately used and in proper working order. Protective equipment includes lead aprons, thyroid collars and leaded glasses, overhanging lead screens (to prevent radiation exposure to the brain), leaded gloves. All such protective clothing should bear an identifying mark and should be examined at regular intervals. Adhering to guidelines and protocols: Every unit or work place that deals with ionizing radiation should have their own local guidelines and rules for radiation safety, keeping in line with international guidelines. These must be read, understood and strictly adhered to in daily practice.

Minimizing the risk of Exposure to Staff and Patients: Every operator who undertakes a cardiovascular procedure in the cath lab is responsible for the amount of radiation exposure to the patient, his or her co-staff and to themselves. Only essential staff shall be in the cath lab during exposure. All persons not required in the room should leave the room during serial radiographic exposure. The operator shall stand behind a barrier if possible. People who must move around the room during the procedure should wear a wraparound protective garment (lead apron, thyroid collar etc.). If possible, the cardiologist and his team in the room should step back from the table and behind portable shields during cine and serial radiography procedures.

 X-ray Equipment Performance and Calibration

Following requirements are necessary: i) Adequate total filtration to be present. ii) The fluoroscopy timer should terminate the exposure or produce an audible signal at the end of a five-minute accumulative time interval. iii) During fluoroscopy, x-ray field collimation and alignment with the image intensifier is to be appropriate. iv) Fluoroscopic exposure rates should not exceed the regulatory standards.

Pregnancy and Radiation As a general rule, sensitivity of a tissue to radiation is directly proportional to its rate of proliferation. Therefore, one could confer that the human fetus, because of its rapid progression from a single cell to a formed organism in nine months, is more sensitive to radiation than the adult. In humans, the major deleterious effects on the fetus include fetal miscarriage, teratogenicity, mental retardation and the induction of cancers such as leukemia that appears in childhood. Fortunately, not all exposures to ionizing radiation result in these outcomes. Fetal risk is a function of both gestational age at exposure and the radiation exposure. The pregnant staff should generally minimize their time spent in the cath lab and should ideally try to stand in the room where the possibility of radiation exposure is minimum. Although doses to the cath lab personnel are high, they may be minimized by practicing ALARA (As Loe As Reasonably Achievable).By minimizing dose to the mother, the dose and the risk to the fetus will also be minimized.

Conclusion: There have been continuous increases in the frequency of diagnostic and interventional cardiac catheterization procedures. It is of paramount importance that that radiation protection in the cath lab must be a matter of primary concern. Strict measures are to be taken to avoid unnecessary radiation exposure not only to medical staff but also to patients. In our country, concerned authority – both in public and private sectors should play more vigilant role to help the cardiac centers develop and practice such radiation protection measures. Concerned professional body and Government should also monitor such activities in cardiac centers having cath lab facility. Relevant professional body is also responsible for constructing local guidelines. Education on radiation hazard, safety and its prevention is badly needed. Continued training of related personnel and awareness in this direction is equally important.

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