Assessment of Beam Alignment, Collimation and Half Value Layer of Some Selected X-Ray Machines in Plateau State, Nigeria

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1 International Journal of Innovative Scientific & Engineering Technologies Research 5(4):-5, Oct.-Dec., 07 SEAHI PUBLICATIONS, 07 ISSN: X Assessment of Beam Alignment, Collimation and Half Value Layer of Some Selected X-Ray Machines in Plateau State, Nigeria M. I. Ike-Ogbonna, D. I. Jwanbot, E. E. Ike, U.A.I. Sirisena, I.A. Joseph Department of Physics, University of Jos, Nigeria Radiology Department, Jos, University Teaching Hospital, Nigeria of corresponding author: ABSTRACT To optimize radiation dose received by patient undergoing x-ray examination, the parameters of x-ray machine need to be assessed to ascertain their functionality. The status of the beam alignment of the x-ray tube, collimator of the light field and the Half Value Layer (HVL) were studied, using a Gammex 6B collimator test tool, Gammex beam alignment test tool model 6A,Gammex 5A HVL set and with a diavolt kv meter. Five x-ray machines 50% (M, M, M, M5 and M9) were all found to be within the tolerance limit of.5 o for the beam alignment test, while 50% (M4, M6, M7, M9, M0) were above the required tolerance limit. Collimation of light field test showed that, M, M, M4, M5, M7, M9, M0 and M were all misaligned within the allowed limit of ±cm, while M and M8 was above the limit. The observed values of HVLs test varied between.4mm and 4.5mm with the recommended value of.5mmal. 50% machines were within the range of the recommended value while 50% were above the recommended value. This implies that maintenance check is required on some of the machines studied in order to improve image contrast and protect patients from unwanted exposure. Keywords: x-ray machine, beam alignment, collimation, tolerance limit, image contrast. INTRODUCTION Medical exposure remains the largest artificial source of exposure of humans to ionizing radiation, hence there is need for maintenance and evaluation of the exposure parameters of the x-ray machines to ensure radiation protection and radiation dose optimization. X-ray images must meet a certain level of quality; to minimize errors of interpretation and allow an accurate diagnosis with low radiation dose. Bad quality image causes the repetition of imaging, duplication of radiation dose to the patient, and also additional costs. (Ai-Kinani, 0). Accurate collimation and beam alignment helps in reducing the amount of scattered radiation arriving at the area under examination and hence prevents other parts of the body from unwanted exposure which minimizes repeat of examinations. Tube filtration is necessary to remove low energy photons from the x-ray beam which could add to the patient s dose. HVL is that thickness of absorbing material that reduces the intensity of X-ray beam to one half its original values and is a function of X-ray tube age, voltage waveform and kvp. (Rehani, 995). HVL Value of the X-ray beam is used to judge the adequacy of filtration and this reflects the penetration power of the beam. Too low filters will allow low energy X-ray to fall on the patient which increases the patient-dose without any enhancement of diagnostic information (ICRP, 007). Too high X-ray reduces the contrast leading to loss of details. It is recommended that beam alignment test and collimator test done within the period of 6months and half value layer test be done annually or after replacement of the X-ray tube assembly (AAPM,988).

2 Degrees of beam alignment Ike-Ogbonna et al.. Int. J. Inno. Scientific & Eng. Tech. Res. 5(4):-5, 07 MATERIALS AND METHOD Beam Alignment, Collimation and Congruence Using a Gammex 6B collimator test tool and Gammex beam alignment test tool model 6A.The tools are placed on a loaded film cassette which is then placed on the radiographic table and the beam alignment test tool is placed at the centre of the collimator test tool with steel balls at both ends aligned. With a fixed kvp and mas which depended on the chemical strength of the developer at a focus to film distance of 00cm, an exposure was done on a well collimated light field at the marked rectangle of the collimator test tool. When radiographic film is developed the collimation on the marked etching surface was seen on the radiographic film and the positions of the two steel balls. The beam alignment, if the image of the two balls overlaps the beam is 0.5 o, if the top ball intercepts the first circle, the beam is.5 o away from perpendicularity and if on the second circle, the misalignment is o. Half Value Layer (HVL) The half value layer was measured using Gammex 5A HVL set for each x-ray machine at a focus field distance (FFD) of 00cm on a fixed kvp and mas which depends on the frequently used kv. The diavolt kv meter was placed on a grid placed on the radiographic table. The x-ray beam was centered on the meter and the light field was collimated to the kv meter. An initial measurement is done and recorded with no aluminum attenuator filter covering the light field. Sequent readings are then taken by varying the alloy aluminum attenuator filter from,,, 4 and 5mm by taping the filter at the face of the collimator. With the kv meter in place a deceasing value of radiation dose was measured. The HVL of the x-ray beam is determined by plotting dose verse aluminum thickness filters. RESULTS The results of three quality control test which was conducted on x-ray machines with two machines having faulty collimator light is shown in tables - and figures - Table : Beam Alignment Test Result M M M M4 M5 M6 M7 M8 M9 M0 M M.5 o 0.5 o 0.5 o.0 o.5 o NA.0 o.0 o.5 o.0 o.0 o NA Legend: M x-ray machines, NA- not available, greater than M M M M4 M5 M6 M7 M8 M9 M0MH X-ray machines Figure : A Bar Chart of Beam Alignment (.5 o ) for X-ray Machines M-M

3 Ike-Ogbonna et al.. Int. J. Inno. Scientific & Eng. Tech. Res. 5(4):-5, 07 Table : Light Field Collimation (±cm or ±%) for x-ray machines M M Machines Right Left Up Down Congruence Remark Code In out In out In out In out M % Fail M % Pass M % Pass M % Pass M % Pass M6 NA NA NA NA NA M % Pass M NA Fail M % Pass M % Pass M % Pass M NA NA NA NA NA NA- Not Available, M- X- ray machines

4 Values of HVLs(mmAl) Ike-Ogbonna et al.. Int. J. Inno. Scientific & Eng. Tech. Res. 5(4):-5, 07 Table : Half Value Layers for Machines M-M (.5.5mmAl) Al M M M M4 M5 M6 M7 M8 M9 M0 M M thickness dose(μgy) Hvl /mmal M M M M4 M5 M6 M7 M8 M9 M0 M M X-ray machines Figure : A Bar Chart of Half Value Layers (HVLs) for M-M. DISCUSSION Table and figure show that beam alignment test for M, M, M, M5 M9 were all within the recommended tolerance limit of.5 o (Rehani, 995) while M4, M7, M8, M0, M were above the required tolerance limit. Table shows collimation with M, M, M4, M5, M7, M9, M0 and Mall misaligned within the tolerance limit of ±% ( AAPM, 00) while M and M8 were above the tolerance limit. The Half Value Layer result from table shows an appreciable decrease in absorbed dose with increase in filter thickness for all diagnostic x-ray machines studied. The observed values varied between.4mm and 4.5mm with the recommended value of.5mmal at 70kVp and.mmal at 80kVp[(APPM, 988). 50% of the x-ray machines M, M4, M6, M7, M0 and M were within the range while 50% (M,M,M5,M9,M andm) were above the range. It may be caused by the shift in the position of the light field, reflecting mirror and anode focal spot. The test was not done for two x-ray machine because of the state of the machine at the time of the study. In comparison with pervious works done on assessment of quality control tests on beam alignment, collimation and x-ray beam filtration by Ismail et al., 05, Okeji et al., 06, Sungita et al., 006, Akagerger et al., 06 and Al-kinani & Yassin.,0, result of some of the studied hospitals (Ismail et al and Akagerger et al.,) have good level of compliance with the recommended standard for most of the x- ray machines,while other studies (Okeji et al and Al-kinani & Yassin et al) show a high level of machines non compliance to the recommended standard. 4

5 Ike-Ogbonna et al.. Int. J. Inno. Scientific & Eng. Tech. Res. 5(4):-5, 07 CONCLUSIONS The aim of the study to assess the beam perpendicularity, collimation and half value layers of the x-ray machines was achieved. The misalignment of the x-ray machine above the tolerance limit should be checked as it affects the patient s dose and image quality. Some of the x-ray machines may need manual adjustment for the x-ray beam to become perpendicular to the image receptor and regular quality control test to be implemented. REFERENCES American Association of Physicists in Medicine.(989). Protocols for the radiation safety surveys of diagnostic radiological equipment. (Report 5).New York: Author. American Association of Physicists in Medicine. (00). Quality control in diagnostic radiology. AAPM Report 74. New York: Medical Physicists Publishing. Available from: medicalphysics.org. Akaagerger, N.B., Agba, E.H., & Ige, T.A. (06): Diagnostic x-ray machines quality control parameters analysis in some major hospitals in Benue State Nigeria. International Journal of Research, (), Available online at hhttps://edupediapublications.org/journals. Al-kinani, A.T., & Yassin, M. (0). Study of the quality assurance of conventional x-ray units at medical city in Baghdad. Merit Research Journal of Medicine and Medical Sciences, (5), Available online at International Commission on Radiological Protection (007). International Commission on Radiological Protection, the 007 Recommendations of the International Commission on Radiological Protection, Publication 0, Elsevier. Ismail, H.A., Ali, O.A. Omer M.A., Garelnabi, M.E., & Mustafa, N.S. (05). Evaluation of diagnostic radiology department in term of quality control of x-ray units at Khartoum State Hospitals, Sudan. International Journal of Science and Research, 4(), Okeji, M.C., Idigo, F.U., Anakwue, A.C., Nwogu, U.B., & Meniru, I.O. (06). Status of Light Beam Diaphragm and its implication in radiation protection in some government and private radiology departments /centres in Enugu State. World Applied Sciences Journal, 4 (7), Rehani, M.M (995). Diagnostics imaging quality assurance. India: st edition Jaypee Brothers medical publishers Ltd Sungita, Y. Y., Mdoe, S. S.L., and Msaki, P. (006). Diagnostic x-ray facilities as per quality control performances in Tanzania. Journal of applied clinical medical physics,7 (4)