Assessment of entrance skin dose and effective dose of some routine x-ray examinations using calculation Technique

Abstract

Introduction X-rays play an important role in diagnosing and treating many kinds of diseases. This important medical X-ray role is always associated with biological effects and risks to the patients and medical staff. The growing concern regarding medical X-ray exposure and their possible risks, has resulted in the initiation of quality control programs and patients dose survey and assessment in many countries. Patients dose have been always measured using thermoluminesence dosimeter (TLD) or transmission ionization chamber (TIC). These two dosimeters though highly accurate, are expensive time consuming and may intervene with patient exposure. A much easier and costless method of dose assessment can be done using calculation methods. Aims The aims of the current work were to survey different entrance skin dose (ESD) calculation methods and then use the most accurate calculation method to assess patients’ entrance doses for selected X-ray exams at the Security Forces Hospital in Riyadh. Different organs doses resultant from different X-ray scans will also be assessed. Methods The study was conducted at Security Forces Hospital and was divided into three stages: Stage 1: In this stage survey of all published calculation methods for ESD was conducted. The accuracy of these published methods in comparison with the method that is based on direct measurement of machine output (method 2) was then performed. During this stage, modelings of different parameters necessary for different ESD calculation methods were also done. Stage 2: In this stage the most accurate method (method 2) was used to survey patients ESD for selected general X-ray examinations. Stage 3: In this stage calculation of organs doses that resulted from different X-ray examinations were performed using XDOSE software. Results and discussions The literature review revealed 7 equations for ESD calculation. Five of these equations were adopted in this work, because they depend on parameters that could be known from the measured exposure parameters, results of quality control test or from modeling of published data. The performance of all other methods in comparison with method 2 was assessed in the studied 2470 patients (views). It was noted that apart from method 1, all other methods performed are well compared with method 2. It was also noted that among the other methods (other than method 1), method 3 was superior to methods 4 and 5 (R2=0.9285, P>0.001 for method 3, R2=0.917, P>0.001 for method 4, and R2=0.9266, P>0.001 for method 5.). A new method was also devised and was found to perform better compared to all other methods (R2=0.9985 and P=0.00267). It was also noted that (a part from chest scan) the calculated ESD (using method 2) for most x-ray examinations was less than that published or recommended in other countries. Although, the ESD found in this study was less than that found in other countries, it was noted that (for most scans) the variation in ESD can not be explained by the variation in organ thickness and this may be attributed to the fact that automatic exposure control is not routinely used by the technologists. This was also reflected on the statistical distribution of the ESD. The results of organs doses follow the same patterns as that of ESD. Organs that are within the scanning field receive the highest dose. The ovaries receive the highest dose from LSS ii (0.52 mSv for AP) and pelvic (0.25 mSv for AP) scans. The other scans have no (or minimum) dose burden on ovaries. The testes on the other hand, receive the highest dose from pelvic (0.95 mSv) and LSS (0.1 mSv forr AP) scans. Other scans deliver much lower doses to the testes. The thyroid receive the highest dose from C-spine (0.25 mSv) and chest (0.04 mSv for AP) scans. Other scans deliver variable range of dose to the thyroid. Bones receive the highest dose from the LSS (0.12 mSv for AP) scans. All other scans deliver variable doses to the bones. Uterus receives the highest dose for LSS (0.69 mSv for AP), pelvic (0.34 mSv) and KUB AP (0.02 mSV). Other scans deliver minimum doses to the uterus. On the whole body, the maximum radiation burden was from LSS scan (0.19 mSv for AP). Conclusion All the assessed ESD calculation methods were comparable. The newly suggested method performed is better compared to other methods. The calculated ESD in the current work was found to be (in general) less than that published in other countries. The high dose found in chest scan need reduction from radiology technologists. Neglecting the use of AEC resulted in bad distribution of ESD that can not be explained by variation in organ or patient thickness in most of the studied scans. A new method for ESD estimation was developed and found to perform well compared to other calculation method and software was developed to calculate the ESD (using the new method) and the organ doses using the Monte Carlo pre calculation data.