The biological effects of diagnostic cardiac imaging on chronically exposed physicians: the importance of being non-ionizing
© Andreassi; licensee BioMed Central Ltd. 2004
Received: 09 November 2004
Accepted: 22 November 2004
Published: 22 November 2004
Ultrasounds and ionizing radiation are extensively used for diagnostic applications in the cardiology clinical practice. This paper reviewed the available information on occupational risk of the cardiologists who perform, every day, cardiac imaging procedures. At the moment, there are no consistent evidence that exposure to medical ultrasound is capable of inducing genetic effects, and representing a serious health hazard for clinical staff. In contrast, exposure to ionizing radiation may result in adverse health effect on clinical cardiologists. Although the current risk estimates are clouded by approximations and extrapolations, most data from cytogenetic studies have reported a detrimental effect on somatic DNA of professionally exposed personnel to chronic low doses of ionizing radiation. Since interventional cardiologists and electro-physiologists have the highest radiation exposure among health professionals, a major awareness is crucial for improving occupational protection. Furthermore, the use of a biological dosimeter could be a reliable tool for the risk quantification on an individual basis.
Over the last 30 years, medical cardiology imaging has rapidly grown, becoming an essential part of the cardiology clinical practice. Imaging procedures include conventional imaging tests such as echocardiography, radionuclide imaging, and angiography as well as a newer imaging techniques such as emission computed tomography and magnetic resonance imaging which promise to expand diagnostic capabilities . These techniques widely differ not only for what concerns costs, availability and technical information, but they also differ in environmental and health hazards.
Many cardiac procedures can deliver high radiation doses to the clinical staff . This exposure may represent a significant health risk, resulting in deleterious clinical implications which can affect not only the personnel involved, but also their progeny [3–5]. Unfortunately, many physicians are unfamiliar with radiation biology or the quantitative nature of the risks and, frequently, ultrasound and ionizing radiation risks are misunderstood [6–9]. The purpose of this paper is to discuss the published evidence on health effects of cardiac imaging procedures employing ultrasound and ionizing radiation.
Summary of studies on genetic effects of medical ultrasounds
Author, Year (Ref)
Miller et al., 1983 (14)
Human lymphocytes exposed in vitro
SPPA intensity 100 W/cm2
Stella et al., 1984 (15)
Human lymphocytes exposed in vitro
1 W/cm2; 0.860 MHz; for 40–160 sec
Barnett et al., 1987 (16)
Human lymphocytes exposed in vitro
SPPA intensities from 15 to 135 W/cm2.
Carrera P et al., 1990 (17)
Chorionic villi exposed in vitro
Chorionic villi from exposed pregnant women
2 MHz at 1, 2, 3 h
Diagnostic US for 20 min (in vivo exposure
Miller et al., 1991 (18)
Human lymphocytes from exposed patients
4 patients underwent therapeutic US
4 healthy persons underwent sham-therapeutic US
Martini et al., 1991 (19)
Lymphocyte and lymphoblastoid cells exposed in vitro
5 MHz for 20 sec, 1 min, 5 min, and 20 min
Sahin O et al., 2004 (20)
Human lymphocytes from exposed patients
10 patients underwent 10 session of US therapy at 1 MHz for 10 min and 10 control subjects underwent sham-therapeutic US
Garaj-Vrhovac and Kopjar, 2000 (22)
Human lymphocytes from cardiologists working with Doppler ultrasound
Unit working with colour Doppler US (transducer frequencies 2.5–7.5 MHz.
SPPA intensity 60–110 W/cm2.
Indeed, ultrasound sources do not transmit acoustic energy into air, and only low level ultrasound reaches medical personnel through handling of the probe . Probably, occupational exposure to ultrasound occurs during training procedures . In fact, medical personnel often apply diagnostic ultrasound to themselves during training or during technique demonstrations . Consequently, ultrasound is not harmful like the other types and sources of radiation. However, a recent investigation indicated that medical personnel from a cardiology unit working with colour Doppler ultrasonic equipment had an increased genotoxic damage compared to the control subjects . Therefore, this observation requires further studies in order to determine if chronic exposure to ultrasound might induce genotoxic effects.
Ionizing radiation is known to cause harm. High radiation doses tend to kill cells, while low doses tend to damage or alter the genetic code (DNA) of irradiated cells. The biological effects of ionizing radiation are divided into two categories: deterministic and stochastic effects. Deterministic effects, such as erythema or cataract, have a threshold dose below which the biological response is not observed [23–25]. Some interventional procedures with long screening times and multiple image acquisition (e.g. percutaneous coronary intervention, radio-frequency ablation, etc) may give rise to deterministic effects in both staff and patients [26, 27].
A stochastic effect is a probabilistic event and there is no known threshold dose. The likelihood of inducing the effect, but not the severity, increases in relation to dose and may differ among individuals.
Genetic effects are the result of a mutation produced in the reproductive cells of an exposed individual that are passed on to their offspring. These effects may show up as birth defects or other conditions in the future children of the exposed individual and succeeding generation. Indeed, studies with laboratory animals have provided a large body of data on radiation-induced genetic effects . Recently, these effects have been also observed in studies of people exposed to radiation from Chernobyl disaster, radiation workers and medical radiologists who have received doses of radiation [31–33]. However, no conclusive evidence exists yet [34, 35].
Radiation exposure to cardiologists
The use of radiation in medicine is the largest source of man-made radiation exposure. According to the latest estimation of the United Nations, an average of 2.4 mSv/year comes from natural sources . In western countries, the exposure dose from medical radiation corresponds to 50 to 100% of the total natural radiation. In 1997, the German Federal Office for Radiation Protection reported 136 million x ray examinations and 4 million nuclear medicine diagnostic tests, resulting in a mean effective dose of 2.15 mSv per person per year . Cardiac and interventional procedures account for a large percentage of nuclear and radiological examinations . Of all radiological examinations, 28% are arteriographies and interventions. An additional 2% derive from chest X-rays and 37% from CT: many of them are cardiological referrals. Regarding nuclear medicine, 22% are cardiological scan. These percentages are likely higher now, since the use of cardiac and interventional procedures is increasing.
Cardiac ionizing procedures expose both patients and medical staff to the highest radiation levels in diagnostic radiology, and recently, as the number of diagnostic and interventional cardiac catheterisation procedures has greatly increased, serious radiation induced skin injuries and an excess of cataract development have been reported in exposed staff [37–39]. Furthermore, it has been suggested that fluoroscopic procedures may be a health hazard and increase the risk for brain tumours in interventional cardiologists .
Recommended occupational dose limits by International Commission on Radiological Protection (ICRP).
OCCUPATIONAL DOSE LIMITS/YEAR
Lens of the eye
Skin, hands, feet, and other organs
As a matter of fact, the head dose sustained by cardiologists may reach 60 mSv per year, and may in some cases exceed the occupational limit of 150 mSv per year recommended for the lens of the eye .
However, the correlation between occupational doses and staff radiological risks is not simple, and it is very dependent on equipment, the specialist, and protocols followed throughout the procedure . Many factors can influence occupational doses for the same radiation dose imparted during cardiac procedure. One of the most important factors is that protection tools are available in catheterisation laboratories and are appropriately used . In addition, another likely reason is a lack of knowledge, information and training in radiation protection .
Doctors' knowledge of radiation dose and risk for medical ionising testing
Author, year (Ref)
Radiological Awareness Evaluation
Shiralkar S et al., 2003 (6)
Radiation doses for common radiological investigations.
97% of doctors underestimates dose.
5% believes that US use ionising radiation.
8% believes thatMRI use ionising radiation.
Finestone A et al., 2003 (7)
Mortality risk of radiation-induced carcinoma from bone scan scintigraphy
Mortality risk was identified correctly by less than 5% of respondents.
Lee CI et al., 2004 (8)
Emergency department (ED), physicians and radiologists
Radiation dose and possible risks associated with CT scan
Almost all doctors were unable to accurately estimate the dose.
Only 9% ED physicians believed that there was increased risk.
Correia MJ et al., 2005 (9)
Adult and paediatric cardiologists
Environmental impact, individual bio-risks, dose exposure and medico-legal regulation of medical ionising testing
Only 11%, 5%, 29% and 42% of physicians correctly identified environmental impact, individual bio-risks, dose exposure and legal regulation, respectively.
Probably, this unawareness has its root in the difficult perception of a long-term risk associated to radiation exposure. In particular, the perception of cancer risk, which can have a latency period of many years after exposure, is often elusive. Furthermore, the exact risk at very low doses to a specific individual is further complicated by many factors, such as carcinogenic agents in our environment, cigarette smoke, diet and genetic background.
However, a recent study has estimated that from 0.6% to 3% of all cancers are due to medical X-rays . These figures are impressive but may largely underestimate the true risk, since they are referred to radiological data concerning the 1991–1996. Taking into account current radiological activities, medical radiation is likely to account for at least 20% of cancer in developed countries .
With regard to occupational exposure for radiologists and radiotherapists, available epidemiological studies have been recently reviewed by Yoshinaga et al . An excess risk of leukaemia associated with occupational radiation was found among early workers employed before 1950, when radiation exposures were high. In addition, several studies provided evidence of a radiation effect for breast and skin cancer. To date, there is no clear evidence of an increased cancer risk in medical radiation workers exposed to current levels of radiation doses. However, given a relatively short period of time for which the most recent workers have been followed up and in view of the increasing uses of radiation in modern medical practices, it is important to continue to monitor the health status of medical radiation workers .
To the fatal cancer risk, one must add the risk of non-fatal cancer and major genetic damage transmitted to the offspring. It is relevant to underline that the long-term damage may not include only cancer but also other major degenerative diseases, including atherosclerosis [47, 48]. However, it is important to realize that many difficulties are involved in designing epidemiological studies that can accurately measure the increases in health effects due to low exposures to radiation as compared to the normal rate of cancer. Studies with very large sample size are required in order to quantify the risks of very low doses of radiation. An alternative strategy could be based on the measure of biological effects by using biomarkers as predictors of delayed health outcomes .
Biomarkers in the assessment of radiation exposure
During the last years, the micronucleus assay has become popular since it is fast and inexpensive, and it is considered to be a "biological dosimeter" for exposure to ionizing radiation .
Cytogenetic studies in hospital workers
Author, year (ref)
Exposed Subjects, n
Non-exposed Subjects, n
Correlation with dose (Yes/No)
Bigatti et al, 1988, (54)
63 (physicians, nurses and technicians)
30 (ward nurses and office personnel)
< legal limit.
Barquinero et al, 1993, (55)
26 (hospital workers)
10 (healthy individuals)
Paz-y-Mino et al, 1995, (56)
10 (hospital workers)
10 (healthy individuals)
Vera et al, 1997, (57)
20 (medical staff working at an X-ray department)
20 (general population)
No (Major DNA damage in subjects exposed to both ultrasound and X-ray)
Bonassi et al., 1997, (58)
871 (hospital workers from 4 laboratories)
617 (healthy individuals)
Available only partially and variable.
Rozgaj et al, 1999, (59)
483 (radiologists, pneumologists, technicians)
160 (healthy individuals)
Undeger et al., 1999, (60)
30 (nurses, technicians, office personnel)
50 mSv/ year.
Cardoso et al, 2001, (61)
8 (workers in X-rays, radiotherapy and nuclear medicine sectors)
8 (healthy individuals)
Maluf et al, 2001, (62)
22 (hospital workers)
22 (non-exposed workers)
0.2 – 121. mSv
Maffei et al, 2002, (63)
37 (physicians, technicians)
37 (non-exposed workers
35 mSv /life
Bozkurt et al, 2003, (64)
16 (nuclear medicine)
16 (non-exposed physicians)
Garaj-Vrhovac and Kopjar, 2003, (65)
50 (physicians, 25 technicians, 10 nurses)
50 (healthy students and office employees)
Maffei et al, 2004, (66)
34 (physicians, technicians)
35 (non-exposed workers)
Zakeri et al., 2004, (67)
71 (cardiologists, nurses and technicians)
36 (healthy individuals)
Andreassi et al, 2004, (67)
31 interventional cardiologists
31 clinical cardiologists
As matter of fact, our results and a recent monitoring of personnel working in angiocardiography laboratories in Iranian Hospitals showed a high frequency of chromosome aberrations in cardiologists s and technicians compared to unexposed subjects [68, 69].
Taken together, these evidences highlight that the use of a biological dosimeter could complement the data obtained by physical dosimetry and reduce the uncertainties of low-dose radiation risk assessment . The analysis of chromosome aberrations is the gold standard endpoint for radiation biological dosimetry. Limitations and strengths on biodosimetry have been fully discussed in the IAEA Report 405 . A possible limitation is the response to high radiation dose (> 4 Sv) where cell death and delays in progression through the cycle represents a pitfall for estimation of acute irradiation particularly when non-uniform or partial body irradiation have occurred.
Moreover, the method is laborious, time consuming and requires expert skills. Scoring of micronuclei has been proposed as an alternative to conventional chromosome aberrations analysis, being more sensitive and faster . Although micronuclei method has been improved, inter-laboratories discrepancies have emphasized the need for better standardization .
Occupational exposure can occur in cardiological procedures which employ ultrasound and ionizing radiation. Today, there are no consistent adverse biological effects on operators caused by exposures to ultrasound. However, it is clearly necessary to continually monitor both the potential risks and safety of ultrasound exposure. In contrast, exposure to ionizing radiation may result in adverse health effect on both cardiologists directly and on their progeny. Although the current risk estimates are clouded by approximations and extrapolations, most data from cytogenetic studies have reported an enhanced DNA damage in hospital workers exposed to chronic low doses of ionizing radiation. The occupational dose of interventional cardiologists, and electrophysiologists tend to be higher compared to other medical specialists as a result of the recent increasing use of interventional techniques. On the other hand, physicians are dramatically unaware of dose, long-term risks and populations health impact caused by the use of medical ionizing radiation. Thus, a major awareness appears to be crucial in order to improve both one's knowledge on the appropriateness of protective tools and also in trying to reduce the number of unnecessary procedures. The use of a biological dosimeter could be a reliable tool for risk quantification on an individual basis.
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