Estimation Of Organ Equivalent And Effective Doses From Diagnostic X-Ray

Project and Seminar Material for Physics

Estimation Of Organ Equivalent And Effective Doses From Diagnostic X-Ray


The radiation dose received by the patient during the radiological examination is essential to prevent risks of exposure.A study was carried out to establish the trend of dose received by patient during x-ray examination in Federal Medical Centre, Keffi in Nasarawa state, Nigeria. Entrance skin doses (ESDs) for a common type of x-ray procedures, namely chest AP/PA (anterior/posterior) were measured. A total of 200 data were collected from patients who were exposed to diagnostic X-ray during their routine chest X-ray examinations. The patent’s skin dose were determined using Edmond’s formula, which is based on the X-ray tube and the radiographic exposure parameters of kVp, mAS, SSD and the total filtration of the beams. The calculated mean skin dose ranges from 0.013 ± 0.01mGy to 0.851±0.023mGy. In general, the ESDs measured for this type of x-ray procedures were found to be lower than or in agreement with the guidance level set by the Nigerian Basic Ionizing Radiation Regulation (NBIRR, 2003) standard and other international bodies and does not pose any significant health risk to the patience or the workers.

Chapter One


In medicine, ionizing radiation is used for two main purposes; diagnosis and therapy. Consequently, individuals and the populace at large receive significant exposure to radiation. Diagnostic radiology is a leading cause of man-made radiation exposure to the population. It was estimated that diagnostic radiology and nuclear medicine contributed 96% to the collective effective dose from man-made sources in the U.K (National Radiology Protection Board, (NRPB, 1993). Similar estimate showed that this contribution was 88% in the U.S.A (National Council on Radiation Protection and Measurement (NCRP, 1987).The health of the population would decline if ionizing radiation techniques were not available to diagnose disease and detect trauma. Nevertheless, there is no excuse for complacency and it is a basic premise of radiation protection practice that any exposure should be justified by weighing the potential harm against the perceived benefit. In view of the significant benefits from properly conducted medical exposures, the principal concern in radiological protection is the reduction of examinations that are either unlikely to be helpful to patient management or involve those that are not as low as reasonably achievable in order to meet specified clinical objectives. In order to do this, there is a need to optimize x-ray equipment and logical techniques (NRPB 1990). Patient dose measurement is an integral part of this optimization procedure (Faulkner, et al 1999). Such measurements will reveal x-ray facilities with doses after which possible dose reduction measures may be specified. Dose measurement is also necessary so as to: establish dose constraints, determine risk to patient and to justify the examination. The current philosophy of the International Commission on Radiological Protection (ICRP) in medical practice is that any use of radiation should be justified. After justification, it is important to optimize the procedure. In radiography this means using as low a dose as reasonable to obtain an optimum image of diagnostic quality.

There are two categories of doses to patient which are important in diagnostic radiology; the effective dose E, which takes into account of dose equivalent to radiosensitive organs and the entrance skin dose. Most interest in diagnostic radiology is concerned with effective dose since this relates to the risk of stochastic effect such as cancer induction.

Drek,(2010) suggested that for public health management of radiation emergencies, one of the essential components of integrated risk assessment is to quickly and accurately assess and categorize the exposure .Radiation safety, monitoring, and assessment have become issues of great concern, since at high doses, ionizing radiation is carcinogenic and clinical symptoms are known to be associated with low-dose exposure. The injuries and clinical symptoms induced by exposure to ionizing radiation include, direct chromosomal transformation, indirect free-radical formation, radiation catractogenesis, cancer induction etc. (Serro, 1992).

Diagnostic X-rays are used for identifying diseases and other problems during medical examinations. The objective of any diagnostic X-ray examination is to produce images of patients with essential details and sufficient image quality so as to guide practitioners for effective and efficient diagnosis and treatment of various disease conditions. Because of the risks associated with the exposure of the patients to X-rays during the diagnostic X-ray examinations, it is suggested that minimum amount X-radiation should be used and the entrance skin dose should be measured and monitored. It has been demonstrated by Edmonds, 1984 that X-radiation to patients depends on the exposure parameters of kVp, mAs, SSD and the filtration.

Standard chest examination consists of Posterior-Anterior (PA) Anterior Posterior (AP) and lateral chest X-ray. The films are read together in radiology department, a chest radiograph commonly called chest X-ray (CXR) is used.
The two fundamental objectives of this research are; first to measure the patient entrance skin dose in order to have a means for setting and checking standards of good practice as an aid to the optimization of patient protection. Secondly, to estimate the absorbed dose to tissues and organs in the patient in order to determine the risk so that diagnostic techniques can be properly justified and cases of accidental over exposure will be properly investigated.

1.1 Background of the Study

Nowadays human organ imaging is performed by different systems and methods. As the new diagnostic methods including conventional radiography, fluoroscopy, and computed tomography (CT) procedures will continue to provide tremendous benefit to modern health care, radiography is expected to be in progress as well, because it is still a powerful tool with enough benefit for the patients undoubtedly. Therefore, patients’ exposure to radiation has been increased all over the world due to this radiography (The 2007 Recommendations of the International Commission on Radiological Protection, ICRP publication 103, 2007; European Commission, European Guidance on Estimating Population Doses from Medical X-Ray Procedures. Radiation Protection N.154, 2008; Fazel et al., 2009; Hart et al, 2010; United Nations Scientific Committee Effects Atomic Radiation, 2010). A wide range of radiation absorbed doses is delivered to patients by the various diagnostic imaging modalities that use ionizing radiation. Even though these procedures are assumed to produce a net benefit, the potential for radiation-induced injuries to the patient exists (The AAPM/RSNA Physics Tutorial for Residents Typical Patient Radiation Doses in Diagnostic Radiology 1, 1999). Since using ionising x-rays is associated with some risk of developing cancer, the basic radiation protection concept or philosophy ALARA states that all exposures must always be kept ‘As Low As Reasonably Achievable’ (National Council on Radiation Protection and Measurements, 1990).

So, the knowledge of the radiation dose received by the patient during the radiological examination is essential to prevent risks of exposures that involve a great number of people. Various indicators are used to estimate detriment from cancer and genetic effects of radiation. According to ICRP 60, the basic quantity associated with the risk of deleterious effects on health is the effective dose that is the valuable and central quantity for dose limitation in the field of radiological protection of the patient (International Commission on Radiological Protection, 1991). This dose descriptor is being increasingly used to determine the quantity of radiation dose received by patient undergoing diagnostic x-ray examinations (Brenner and Huda, 2008; Kharita et al., 2010; Mettler et al, 2008; Osei and Darko, 2013; Shahbazi-Gahrouei and Baradaran-Ghahfarokhi, 2013; Teles et al., 2013). Whereas effective dose (ED) is affected by patient structure and radiological method, as such, the calculation of this quantity is of utmost importance. Because it is almost impossible to directly measure effective dose during clinical procedures, it must be determined indirectly.

In general, indirect estimate of effective dose starts from incident air kerma (Ka,i) measurement as input parameters and uses dedicated conversion coefficients (European Commission, European Guidance on Estimating Population Doses from Medical X-ray Procedures, Radiation Protection N.154, 2008; International Atomic Energy Agency, 2007; International Commission Radiation Units, 2005). Entrance skin dose (ESD) is also an important parameter in accessing the dose received by a patient in a single radiographic exposure. The European Union has identified this physical quantity as one to be monitored as a diagnostic reference level in the hopes of optimizing patient dose (Bushong, 2001 and ICRP, 1991).

1.2 Aim of Study

The aim of this work is to study the estimation of organ equivalent and effective doses from diagnostic x-ray.

1.3 Scope of Study

This research work is carried out to establish the trend of dose received by patient during x-ray examination in Federal Medical Centre, Keffi in Nasarawa state, Nigeria.

1.4 Problems of Study

The problems associated with this work were mainly financial constraints encountered during the execution of this project, limited sources of materials and difficulties in acquiring data for analysis.

Chapter Five

5.0 Conclusion and Recommendation

5.1 Conclusions

The results presented in this research work indicate that the ESDs received by patients undergoing x-ray examination in medical centreKeffi were within the guidance levels of 0.4mGy set by radiation protection bodies. Considering the condition of the machine used for this examination, a reference skin dose of 1mGy can still be compared with the skin doses evaluated in this research. It is possible that the x-ray machine is properly maintained, although all x-ray machines have to pass through quality control evaluations after each three months before it be allowed to operate. Owing to the fact that the maximum absorbed dose recorded in this research is 0.851mGy which is a bit higher than the guidance level, we therefore have to make the following recommendations.

5.2 Recommendation

Under age patients undergoing radiological examinations should be given special considerations by cutting down doses using high kilovolt technique and lower mAs. The ALARA (as low as reasonably achievable) principle should be used when carrying out x-ray activities. Consistency in Quality Assurance program and training of personnel will go a long way in reducing the radiation doses received by the patients. The estimation of stochastic risk to Keffi population as a result of X-ray diagnostic procedures and the establishment of dose reference levels in Keffi Medical Centre Radiological Unit are guide for future monitoring and studies.

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