Risks of Ionizing Radiation in Medical Imaging - Report Example

The Risks associated with Ionizing Radiation in Medical Imaging practice, and the Precautions required for Protection against them. Medical imaging has, of late, revolutionized the field of modern medicine, emerging as an undeniable lifeline for early detection and diagnosis of diseases. Medical imaging coupled with radiation therapy has reduced the need for invasive surgeries and therapies, thereby shortening the time taken for recovery. It has also emerged as an efficient tool for targeted cancer treatment. Medical imaging involves the use of both ionizing and non-ionizing radiation. Medical imaging involving ionizing radiation uses x-rays and gamma rays. As the ionizing radiation passes through the body, it is differentially absorbed by tissues of greater thickness, causing ionization of tissue atoms making them chemically reactive and potentially capable of cell damage (Yale 2011). This raises concern over the frequent use of ionising radiation in medical imaging, and the associated risks to human health. Exposure to ionizing radiation is of concern because evidence has linked exposure to low-level ionizing radiation at doses used in medical imaging to the development of cancer. The National Academy of Sciences’ National Research Council comprehensively reviewed biological and epidemiological data related to health risks from exposure to ionizing radiation, recently published as the Biological Effects of Ionizing Radiation (BEIR) VII Phase 2 report. The epidemiologic data described atomic bomb survivors, populations who lived near nuclear facilities during accidental releases of radioactive materials such as Chernobyl, workers with occupational exposures, and populations who received exposures from diagnostic and therapeutic medical studies. Radiation doses associated with commonly used CT examinations resemble doses received by individuals in whom an increased risk of cancer was documented. For example, an increased risk of cancer has been identified among long-term survivors of the Hiroshima and Nagasaki atomic bombs, who received exposures of 10 to 100 milli-sieverts (mSv). A single CT scan can deliver an equivalent radiation exposure, and patients may receive multiple CT scans over time. (Smith-Bindman et al 2009) Risks involved in the use of Ionizing radiation Since the finding of the first solid tumour that resulted from the effects of ionizing radiation, protection from ionizing radiation used in medical procedures has become a vital issue, particularly in view of the dramatic increase in the number medical procedures involving its use (Davros et al 2007). Because of the public uproar over radiation protection, an International Commission for Radiation Protection was established in 1928. "The International Commission on Radiological Protection (ICRP) estimates that the average person has an approximately 4-5% increased relative risk of fatal cancer after a whole-body dose of 1 Sv. However, other studies on multiple cohorts of radiation workers have largely failed to establish statistically significant cancer risks. When multiple occupational cohorts were combined and evaluated in a somewhat systematic way, a combined excess relative risk of cancer death of just less than 1% was estimated" (Cardis et al 2005). During the 1950s and 1960s, there were an increasing number of indicators that ionizing radiation was dangerous to humans. Experimentation using X-rays on animals, particularly rats, have linked ionizing radiation exposure to impending death, even at low levels. It has been proved that high and more frequent doses of radiation pose greater risks to the patient, causing, for example, skin erythema and other kinds of irritations (Egbe et al 2009). Other side-effects of ionizing radiation include dizziness, nausea, and light headedness. Risks associated with radiation exposure in hepato-biliary scans are quite high. In a study by McCollough et al (2009) it was found that in many cases, the onset of cancer was linked to the area frequently exposed to x-rays. Other studies suggest that "0.4% of cancer cases in the United States are related in some way to ionizing radiation and 1.5 – 2.0% of organ specific cancers are related to the ionizing radiation from medical procedures" (McCollough et al 2009). In another instance, Chau et al (2008) have pointed towards the risk of biological effects of ionizing radiation on pregnant women. Precautionary measures and safety issues In order to avoid the negative health consequences associated with radiation therapies, the patients exposure to radiation must be limited by all means possible. This situation led to the postulation of ALARA, a radiation safety regulation principle. It is an acronym for As Low As Reasonably Achievable, aiming at minimization of the radiation dose by all reasonable measures. It is the mainstay of modern radiology. According to the ALARA regulation, radiologists and medical imagers, while conducting medical imaging involving ionizing radiation, need to take all precautionary steps possible to enable achievement of desired image quality, without exposing the patient to excess, often unnecessary radiation. Exposure is the most important term in radiology (Durham 2007). Another major area of concern is the radiation exposure of the personnel and staff involved in medical imaging practices (Tsiklakis et al 2005). Personnel in radiology departments of hospitals and imaging centres are exposed to radiation on a daily basis. For operators working in radiography, the maximum dose limit is 20mSv. It is important that all radiology staff use a dosimeter (Bor et al 2009; delle Canne et al 2006). As a safety procedure, the operator and personnel should wear lead protective aprons, and the dose level should be regularly monitored. Thermo-luminescent dosimeters (TLDs) should be placed under the lead aprons. In case of areas not covered by the apron, like fingers and eyes for example, the dose limit may exceed 20mSv. Operators performing X-rays on a regular basis also tend to exceed the dose limit and may be affected by the accumulated hazards of radiation. Fortunately, these risks can be avoided by regular and closer monitoring of the exposed organs and of the overall health of the operator, in order to make sure that he/she does not exceed the annual dose limit (McCollough et al 2009). In case of fluoroscopy, additional precautionary measures should be implemented, like adjusting a suitable field size, kV and mAs until an acceptable exposure level is obtained (Topaltzikis et al 2008). In order to reduce the risk of over exposure, timing is a very important factor. Moreover, precautions should be taken to protect the eyes from exceeding the dose limit, such as the use of a suspended shield (Muhogora et al 2006). The use of a suitable filter can effectively reduce the hazardous effect of radiation. The effectiveness of a filter is dependent on its type and thickness (Triantopuolou et al 2005). The type and thickness of the filter affects the quality of the image. Copper sheeting filter, for example, processes good quality images, reducing the dose level to the patient at the same time. Nowadays, newer safety techniques concerning radiation exposure have been investigated and implemented. The procedures have become more advanced and more complex. Need for Image optimization and techniques for risk reduction While reducing the risk to patients, personnel and staff is of top-most priority, there is also a need to find ways to improve the quality of the image obtained in medical imaging. Although the exposure level must be minimized to the greatest extent, the quality of the image obtained must also be kept at a satisfactory level. This is known as optimization (Matthews and Brennan 2008). This is especially true for all of the different purposes of ionizing radiation such as dental radiation (Gavala et al 2008). The use of automation control or automatic exposure control, for example, can monitor the quality of the image, minimizing the exposure level at the same time (Imhof et al 2003). There are various techniques that reduce radiation dose without compromising on the image quality. Most imaging techniques produce an unsynchronized image (rate up to 60 frames per second). Synchronized output, however, can considerably reduce dose level but also increases the contrast of the images. For instance, in some cardiac operations, the operator can use a rate as low as five frames per second. This can reduce the radiation dose level to the minimum. But, this technique has a drawback. The amount of noise increases when the frame rate decreases. This drawback can be balanced by adjusting the mA which in turn ensures the quality of the image. Dose level can be greatly reduced if we have a greater tolerance to noise and jerky images. However, this approach is underused because of some misconceptions on image quality. To avoid these issues, a number of theoretical frameworks can be implemented, such as the Quality Function Deployment model (Moores 2006). The dose level can also be reduced by using the dose spreading technique. This is another example of optimization (Triantopoulou et al 2005). The C-arm of the machine is rotated, but at the same time the intervention site is kept in the centre of the field of view. This can minimize the hazardous effects of radiation on skin, especially when used in a longer procedure where higher than normal dose is involved. However, the operator must pay attention to use a small beam in this case. The operator’s procedures will not be interfered by the small movements of the C-arm arm rotation. When larger fields are involved, bigger ratios of movement are necessary. The operators may be affected during some procedures involving movement that can be up to 180 degree. In this case, it is more suitable to divide the dose with negligible interference. Ultra low dose fluoroscopy imaging automation is another possible means to reduce the dose level. However, it is still in a developmental stage. Since the operator is responsible to set the parameters of the machine (kV,mA), the experience of the operator becomes critical in this case. An inexperienced operator provides substandard images in such an examination. The ultra low dose fluoroscopy can be continually controlled using a computer, to be applied to the area of interest during an examination. This minimizes the effects of radiation on staff and personnel. Another technique for reduction of radiation exposure is by the use of digital fluoroscopy, where the image is held on the display (Triantopoulou et al 2005). While the operator is studying the still image, no radiation is used on the patient. The image can also be used as a reference image by transferring it to another monitor. In this way, the dose level can be reduced to the minimum. The still image can also be used in the road mapping technique. In difficult angiographic digital fluoroscopy, a reference image is used to compare with the image obtained from pulse fluoroscopy. This can increase the visibility of vessels of interest. Here, the reference image is used as a mask, resulting in an effective navigation through the vascular system, while simultaneously enabling dosage reduction. Interventional angiographic procedures, which use a high quality moving image, do not need to use the full field of view. Dose level can be reduced by using appropriate positioning of the aperture, together with higher intensity beam, and with a lower quality reference image. A phantom image is used as the reference when a region of interest is required for long term use of fluoroscopy. The focus on the region of interest prevents the entire area from long term exposure to radiation. However, this technique still has room for improvement, as it may not be able to provide images of the same quality as the techniques mentioned above. In conclusion, I would like to state that, though various techniques and safety procedures have been investigated and used in order to minimize the danger of radiation exposure, no technique can replace the importance of the experience of an operator. When the staff and patients adhere to all the safety procedures, norms and regulations, valuable medical information can be obtained through radiography, at a much lower risk. The implementation of safety standards is vital in the use of medical imaging, which has proved to be a boon for diagnosis of innumerable diseases and treatment of cancers. The importance of further development of technologies that provide better images at lower radiation doses cannot however be undermined. Such technologies are the need of the hour, more so, in practice than in theory. Reference List Bor, D., T. Olgar, T. Toklu, A. Caglan, E. Onal and R. Padovani. 2009. "Patient doses and dosimetric evaluations in interventional cardiology." Physica medica 25(1):31-42. Canne, S., A. Carosi, A. Bufacchi, T. Malatesta, R. Capparella, R. Fragomeni, N. Adorante, S. Bianchi and L. Begnozzi. 2006. "Use of GAFCHROMIC XR type R films for skin-dose measurements in interventional radiology: Validation of a dosimetric procedure on a sample of patients undergone interventional cardiology." Physica medica 22(3):105-10. Chau, A., and K. Fung. 2008. "Comparison of radioation dose for implant imaging using conventional spiral tomography, computed tomography, and cone-beam computed tomography." Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontology 107(4): 559-565. Davros, W. 2007. "Fluoroscopy: basic science optimal use, and patient/operator protection." Techniques in regional anesthesia and pain management 11: 44 - 54. Durham, J. 2007. "Concepts. Quantities, and dose limits in radiation protection dosimetry." Radiation measurements 41 S28- S35. Egbe, N., S. Inyang, D. Eduwem and I. Ama. 2009. "Doses and image quality for chest radiographs in three Nigerian hospitals." European journal of radiology 1, 30-36. Gavala, S., C. Donta, K. Tsiklakis, A. Boziari, V. Kamenopoulou and H. Stamatakis. 2008. "Radiation dose reduction in direct digital panoramic radiology." European journal of radiology 71(1):42-8. Matthews, K., and P. Brennan. 2008. "Optimisation of X-ray examinations: General principles and an Irish perspective ." Radiography 15(3): 262-26 McCollough, C., A. Primak, N. Braun, J. Kolfer, L. Yu and J. Christner. 2009. "Strategies for reducing radiation dose in CT." Radiol clin N Am 47(1): 27–40. Moores, B. 2006. "Radiation safety management in health care- The application of quality function deployment." Radiography 12:291-304 Muhogora, W., A. Nyanda, W. Ngoye and D. Shao. 2006. "Radiation doses to patients during selected CT procedures at four hospitals in Tanzania". European journal of radiology 57 :461-467 Smith-Bindman, R., Lipson, J., Marcus, R., Kim, K., Mahesh, M., Gould, R., Berrington de Gonzalez, A., & Miglioretti, D. 2009. "Radiation Dose Associated With Common Computed Tomography Examinations and the Associated Lifetime Attributable Risk of Cancer" Archives of Internal Medicine, 169 (22):2078-2086. Accessed April 20, 2011. doi:10.1001/archinternmed.2009.427 Topaltzikis, T., C. Rountas, R. Moisidou, I. Fezoulidis, C. Kappas and K. Theodorou. 2008. "Radiation dose to patients and staff during angiography of the lower limbs. Derivation of local dose reference levels." Physica medica 25:25-30. Triantopoulou, C,. I. Tsalafoutas, P. Maniatis, D. Papavdis, G. Raios, I. Siafas, S. Velonakis and E. Koulentianos. 2005. "Analysis of radiology examination request forms in conjunction with justification of X- ray exposures." European journal of radiology 53:306-311 Tsiklakis, K., C. Donta, S. Gavala, K. Karayianni, V. Kamenopoulou and C. Hourdakis. 2005. "Dose reduction in maxillofacial imaging using low dose cone beam CT." European journal of radiology 56:413-417. Yale Univ. 2008. “Diagnostic imaging modalities - Ionizing vs non-ionizing radiation.” Accessed April 20. http://www.yale.edu/imaging/techniques/ionizing_vs_nonionizing/index.html Read More