Radiation Dose Measurements in Routine X ray Examinations

Transcription

1 Tenth Radiation Physics & Protection Conference, 27-3 November 21, Nasr City - Cairo, Egypt Radiation Dose Measurements in Routine X ray Examinations H. Osman *1, A. Sulieman 1, I.I. Suliman 2 and A.K. Sam 2 1 Sudan University of Science and Technology, College of Medical Radiologic Science. P.O Box 198, Khartoum, Sudan. 2 Sudan Atomic energy commission, Radiation safety institute. P.O. Box 31,Post code 11111,Khartoum, Sudan. [email protected] ABSTRACT The aim of current study was to evaluate patient's radiation dose in routine X-ray examinations in Omdurman teaching hospital Sudan.11 patients was examined (134) radiographs in two X-ray rooms. Entrance surface doses (s) were calculated from patient exposure parameters using DosCal software. The mean for the chest, AP abdomen, AP pelvis, thoracic spine AP, lateral lumber spine, anteroposterior lumber spine, lower limb and for the upper limb were; 231±44 μgy,453±29 μgy, 567±22μGy, 311±33 μgy,716±39 μgy, 611±55μGy, 311±23 μgy, and 158±57 μgy, respectively. Data shows asymmetry in distribution. The results of were comparable with previous study in Sudan. Keywords: Radiation Dosimetry/ X-rays/ / Quality Control INTRODUCTION Radiation protection is an important concept in diagnostic radiology. The most important consideration in protecting the patient is to ensure that images of sufficient quality for accurate diagnosis are produced without the need for any repeat (1). The means to achieve this are the design and maintenance of equipment, training and experience of staff, robust operating procedures (1). There is certain practical method for further dose reduction. Collimation should always be to the region of interest, that mean visualization of the collimator edges on the image confirm that there is no unidentified region of the patient being exposed. Secondly supplementary shielding may be used to protect sensitive structures within the field of view. Radiation to patient in radiology can be reduced further using increased filtration to remove soft X-rays that add to patient exposure but do not contribute to the diagnostic image. (1). Patients can undoubtedly obtain enormous benefit from diagnostic X-ray examinations, although the ionizing nature of the X-rays means that their use is not entirely without risks. For this reason, all exposures to diagnostic X-rays need to be justified and optimized in terms of benefit and risk (2), One of the basic requirements for such requirement is the knowledge of patient doses. In Sudan, as in other third world, not much data are available about radiation dose in diagnostic radiology and in conventional examination as particularly. The only available data 287

2 Tenth Radiation Physics & Protection Conference, 27-3 November 21, Nasr City - Cairo, Egypt to the best of our knowledge in dosemetric diagnostic radiology are for pediatric examination in chest and other common X- ray examinations (3, 4, 5). In this study the entrance skin dose ( ) for the chest, the abdomen, the pelvis, the lateral lumber spine, anteroposterior (AP) lumber spine, the lower limb and for the upper limb are determined for the first time. Comparison with reference doses and previous studies should help in optimizing radiographic examinations in selected hospital. The results presented will serve as a baseline data needed for deriving diagnostic reference dose levels (DRLs) for common X-ray examination in that hospital. MATERIALS AND METHODS A sample of 11 patients was examined with a total of 134 radiographs in Omdurman teaching hospital with dual X- ray department and average workload examination per day. X ray unit specification (manufacturer, X- ray generator, X-ray tube output and filtration) are presented in Table 1. Hospital Table 1: X ray units data and specification Machine manufacturer X ray unit model Max kvp Actual Filtration (mm Al) Tube output (mgy) Omdurman (A) Toshiba DRX-3724HD Omdurman (B) Toshiba DRX-3724HD Extensive quality control test to evaluate kvp accuracy (Tolerance: Maximum deviation should not exceed 1%, Good :± 5 % or 5 kvp, which ever is greater.) (6). Timer accuracy, exposure linearity and reproducibility was calculated according to following formula (6). ( mrmax mrmin ) Re producibil ity = ±.5 (1) mr mr Where respectively. mrmax and mrmin ( ) max min are the maximum and minimum exposure (in mr); Filtration check and darkroom evaluation tests were performed as a part of this study. The two X-ray units successfully passed the predefined tolerance levels. The film screen combination used in both departments was Kodak speed 4 and in previous studies (7, 8) was low and medium speed. For dose calculation, patient individual exposure parameters were recorded (tube peak kilovoltage (kvp), milliampere and exposure time product (mas) and Focus to skin distance (FSD). Patient demographic data (age, gender, weight, height) in addition to the clinical indications were also recorded. Table 2 shows clinical indication. 288

3 Tenth Radiation Physics & Protection Conference, 27-3 November 21, Nasr City - Cairo, Egypt Table 2 shows clinical indication Clinical Indication Gender Male Female Total Trauma TB 2 2 Abdominal pain F.B 1 1 Rheumatic disease Chest infection Osteoporosis 8 8 Renal stones Total Entrance surface doses (s) in this study were calculated using Dose Cal software developed by the radiological protection centre of Saint George Hospital, London, this software is extensively used to calculate patient dose in diagnostic radiology (3). For dose measurement using the software, the relationship between X-ray unit current time product (mas) and the air kerma free in air was established at a reference point of 1 cm from tube focus for the range of tube potentials encountered in clinical practice, the X- ray tube out put were measured in (mgy/mas) using Unfors Xi Dosimeter (Unfors Inc., Billdal, Sweden) with accuracy better than 5%. was calculated according to the following formula (3) : 2 2 = (2) OPx kv 8 xmasx 1 FSD xbsf where( OP) is the output in mgy/ (ma s) of the X-ray tube at 8 kv at a focus distance of 1 m normalized to 1 ma s, (kv) the tube potential,( ma s) the product of the tube current (in ma) and the exposure time(in s), (FSD) the focus-to-skin distance (in cm) and (BSF) the backscatter factor. The normalization at8 kv and 1 ma s was used as the potentials across the X-ray tube and the tube current are highly stabilized at this point.bsf is calculated automatically by the Dose Cal software after all input data are entered manually in the software. The tube output, the patient anthropometrical data and the radiographic parameters (kvp, ma s, FSD and filtration) are initially inserted in the software. The kinds of examination and projection are selected afterwards. The study of Davies et al (7) shows that s calculated using Dose Cal software are within 2% compared with s measured using thermo luminescence dosimeters (TLDs). Another reason for using DosCal software is that the working procedures in crowded emergency department and non co-operative patient to wear TLDs envelope is some what difficult. RESULTS AND DISCUSSION Table 1 shows the X-ray equipment data and specifications. Antiscatter radiation grid was used in all examinations except in upper limb imaging, where the tube voltage is less than 6 kvp and the organ to be examined has small thickness (1). Before data collection extensive quality control test has been performed to evaluate kvp station accuracy, and reproducibility as shown in Table 3(a-d). 289

4 Tenth Radiation Physics & Protection Conference, 27-3 November 21, Nasr City - Cairo, Egypt Table 3(a) kvp accuracy in Omdurman hospital department A Cu sheet thickness (mm) kvp displayed (console) kvp Measured Error of accuracy ( kvp) Error of accuracy % Accepted Yes / No Table 3 (b) kvp accuracy in Omdurman hospital department B Thickness or No of cu sheet kvp displayed kvp Measured Error of accuracy( kvp) Error of accuracy % Accepted Yes / No Table 3(c) reproducibility test in hospital department A Reading Number Exposure mgy Measured Variance (IPEM) Guideline Acceptance Yes.6 ±5% Y NO Table 3 (d) shows reproducibility test in hospital department B Reading Number mgy Measured Variance (IPEM) Guideline Acceptance Yes NO ±5% Y 29

5 Tenth Radiation Physics & Protection Conference, 27-3 November 21, Nasr City - Cairo, Egypt Correlation between and body mass index BMI BMI y = x R 2 =.5484 Linear ( µgy) correlation between and BMI in hospital bfor chest examinations y = x BMI (Kg) R 2 =.4836 Linear ( µgy) Figure 1(a-b) correlation between entrance skin dose (ugy) and body mass index BMI (Kg/m 2 ) of patients undergoing chest X-ray in department A and B respectively. correlation between and patient weight for patient undergoing chest indepartment a y = x R 2 = patient weight(kg) 291

6 Tenth Radiation Physics & Protection Conference, 27-3 November 21, Nasr City - Cairo, Egypt correlation between patient weight (Kg) and for patient undergoing chest examination in department b y = 9.848x patient weight(kg) R 2 =.648 Linear ( µgy) Figure 2 (a-b) correlation (μgy) and patient weight (kg) in department A and B respectively. 1 y = x R 2 = Linear () Kvp Figure 3 correlation between (ugy) and kvp set by operator in both department for different examinations correlation between and Kvp in hospital a for different examination y = x R 2 = Kvp 292

7 Tenth Radiation Physics & Protection Conference, 27-3 November 21, Nasr City - Cairo, Egypt correlation between and Kvp in department b for different examination (ugy) y = x R 2 = Kvp Figure 4 (a-b) correlation between (ugy) and KVp in department A and B for different examination respectively. As shown in Figure 1(a-b) there is linear correlation between (ugy) and body mass index BMI( Kg/m 2 ) of patients undergoing chest X-ray in department A and B with determination coefficient (R 2 ) of.55 and.48 ;respectively. Also figure 2 (a-b) showed linear correlations between (ugy) and patient weight (Kg) undergoing chest X-ray examination in department A and B with determination coefficient (R 2 ) of.81 and.65, respectively. Chest examination was chosen for showing the correlation between and BMI because it s the most frequent exam in both departments and even worldwide. Figure 3 shows a linear correlation between (ugy) and kvp in both departments for selected different examinations. Figure 4(a-b) shows also a linear correlation between µgy) and kvp in both department A and B with determination coefficient (R 2 ) of.4 and.7 respectively. This is a clear indication that kvp values were consistent with as expected. Table 4 comparison between mean (mgy) in different examination and previous study [ 7, 8, 9 ] Examination Present study Kepler.K et al (8) Henner Anja (9) Olivera Ciraj et al (7) PA chest.23 ± ±.14 Thoracic spine and inlet.3±33 N.A N.A.9±.5 AP pelvis.56± ±.9 Lateral lumbosacral spine.71± ±1. AP lumbosacral spine.61± ±1. AP abdomen.45±29 N.A 5 N.A Upper limb.16±57.33 N.A N.A N.A Lower limb.31±23 N.A N.A N.A N.A =no data available The for chest radiographs are comparable to those reported in previous studies (7, 8, 9). Despite that s for AP thoracic in the present study was 66% lower that those reported in Brazil (9). Also present study lower for AP pelvis by 88% and 67% for AP pelvis 293

8 Tenth Radiation Physics & Protection Conference, 27-3 November 21, Nasr City - Cairo, Egypt performed by Olivera Ciraj et al and Henner Anja (7,9) respectively. And for lumbosacral spine AP and lateral it is also reduced by factor of 59%, 9%, 132%, 93% for study of Olivera Ciraj et al (7) and Kepler.K et al (8) respectively. The results of the current work are comparable with previous studies in Sudan [ 3, 7, 8,1 ] CONCLUSION Data shows asymmetry in distribution due to the different patient characteristics. The results of this study were comparable with previous study in Sudan. The usages of slow intensifying screen increases the radiation dose to the patient while increase the image quality by comparison with the previous studies. Further studies are required in order to optimize radiation dose and establish local diagnostic reference level DRL. REFERENCES (1) P. Allisy-Robert, J. Willams; Farr s Physics for Medical Imaging, 2 nd edition, Saunder;43-61(28). (2) International Commission on Radiological Protection, Recommendations of the ICRP. (Publication 6). Annals ICRP 21(1991). (3) I.I. Suliman, E. H. A. Elshiekh; Radiat. Prot. Dosim; 132 (1) (28). (4) O. Ciraj, S. Marković, D. Košutić; the Journal of Preventive Medicine; 12 (3-4): (24). (5) K. E. M. Mohamadain, L. A. R.,Da Rosa, A. C. P. Azevedo, M. R. N. Guebel, M. C. B. Boechat, and F. Habbani. Phys. Med. Biol. 49, (24). (6) Jeffrey PAPP; Quality management in imaging sciences Mosby, New York, (1998). (7) M.Davies, H. McCallum, G. White, J. Brown, M. Helm; Radiography, 3, (1997). (8) K. Kepler1, A. Servomaa,A,. Filippova,I; Preliminary reference levels for diagnostic radiology in estonia. IFMBE proceeding.13 th Nordic Baltic Conference on Biomedical Engineering and Medical Physics(13NBC 25),Umea,Sweden,!3-17 june,pp.29-3.(28). (9) A. Henner; Radiographer students learning dose management of the patients, Proceedings of Third European IRPA Congress 21 June 14 18, Helsin ki, Finland,(21). (1) I. I. Suliman, N, Abbas, and F.I. Habbani. Radiat. Prot. Dosim.123 (2), (27). 294