CHAPTER ONE
INTRODUCTION
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).
Patient doses in diagnostic x-ray examinations can be best estimated in terms of entrance surface dose (ESD) per radiograph or dose area product (DAP) for the complete examination (European Commission, 1996). On the other hand, the effective dose is the best quantity for estimating radiation risks to the patients. The major benefit of using the effective dose is that this parameter accounts for the absorbed doses and relative radio-sensitivities of the irradiated organs in the patients and, therefore, better quantifies the patient risks (ICRP, 1991). Studies aimed at achieving low patient doses with sufficient image quality have continue to be of interest in research (ICRP, 1991 and United Nations Scientific Committee on the Effects of Atomic Radiation, 2000). With the challenges enumerated above, it is therefore important to study the organ equivalent and estimate the effective doses for different diagnostic x-ray projections at General Hospital, Dutsin-Ma Local Government Area, Katsina State