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 Xray 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.
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.
At the General Hospital Dutsin-Ma, large numbers of diagnostic x-ray radiology are conducted yearly for various purposes. However, most examinations carried out do not have records of doses received by the patients. Therefore, adequate radiation dose (patients` organ equivalent and effective dose) management is hindered and difficult. While methods to calculate effective doses have been established, they depend heavily on the ability to estimate the dose to radiosensitive organs from radiological procedure(s). The determination of the radiation dose to these organs is very difficult and direct measurement is not possible. Therefore organs doses are estimated from measurable quantities such as the dose-area product (DAP) or entrance surface dose (ESD) associated with the radiological examination and normalised organ doses data. The exposure to high level of diagnostic x-ray may lead to cancer. There is therefore the need to estimate the organ equivalent and effective dose in order to know whether it poses a health risk to the inhabitants. The imaging procedure should be judged to do more good (e.g., diagnostic efficacy of the images) than harm (e.g., detriment associated with radiation induced cancer or tissue effects) to the individual patient. Therefore, all examinations using ionizing radiation should be performed only when necessary to answer a medical question, treat a disease, or guide a procedure. The clinical indication and patient medical history should be carefully considered before referring a patient for x-ray examination.
1.2 Aim and Objectives
The aim of this study is to investigate patients’ doses from radiological examinations. The objective of this study includes:
To establish some reference and guidance dose values for radiological examinations performed at the hospital.
To monitor any changes over time that might arise from aging equipment or changing protocols, and
To compare the patient’s examinations with that of other hospitals and regions as reported in literature.