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ESTIMATION OF ORGAN EQUIVALENT AND EFFECTIVE DOSES FROM DIAGNOSTIC X-RAY

ABSTRACT

The radiation dose received by the patient during the radiological examination is essential to prevent risks of exposure. The aim of this work is to study organ equivalent and effective dose s for common diagnostic radiographic examinations at General hospital Dutsin-Ma local Government Area, Katsina State, Nigeria. We estimated the entrance surface dose received by patients undergoing diagnostic X-ray examinations, including the entrance surface dose and effective doses for 20 patients in six types of X-ray examinations. The entrance surface dose was determined indirectly via measurements and from knowledge of X-ray output factors. We entered measurement parameters such as X-ray dose output, backscatter factor, and focus to skin distance as well as physical parameters such as mAs and kV in mathematical model. The mean for entrance surface doses and effective doses for chest (PA, AP), abdomen (AP) and skull (AP, Lateral) are 0.2432 mGy, 0.2857 mGy, 0.6331 mGy, 0.7553 mGy, 0.3220 mGy and 0.01216 mSv, 0.01428mSv, 0.07597 mSv, 0.00755 mSv and 0.00322 mSv respectively. The results obtained were compared with those published by some national and international agencies. The entrance surface dose and effective dose reported in this study are generally lower than the comparable reference dose values published in the literature. On the basis of the result obtained in this study, one can conclude that proper use of radiological parameter such as the large distance between patient and X-ray source, high tube potential and low tube current can significantly reduce the absorbed dose which has been shown in this work. When technical and clinical factors are optimized or properly used, patient doses will reduce substantially. Further studies are required for minimization of radiation doses to sensitive organs.

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).