Methodology adopted to establish diagnostic X-ray beam qualities
Introduction
There has been an exponential rise in the use of diagnostic procedures in clinical applications, especially the use of Computed Tomography (CT), Nuclear Medicines and Interventional Fluoroscopy (IF). With the advent of new and specialized diagnostic tools, concern has been raised regarding the radiation dose received by patients and the health care providers involved in these procedures (R and 2000 report; “So, 2000). Although, the risk of developing radiation associated cancer by medical imaging is very small, the cause of concern is the increase in per capita dose as the number of people undergoing these diagnostic procedures is increasing. In view of the importance of patient dose in radiological procedures, there is a need to control patient dose by the principle of optimization along with regulatory control. Many standards and reports have been published internationally to regulate diagnostic radiology, ICRP73 (Publication 73; “Rad, 1996), ICRU 74 (Report 74; “Patient, 2005), IEC 61267 (C 61267 and “Medical diagn, 2005) and IAEA TRS 457 (Technical Reports Series, 2007) and help establish Diagnostic Reference Levels (DRLs).
DRLs are based on dosimetric quantities and are values which ensure no compromise on the intended purpose of diagnosis with optimal radiation dose to the patients. For the successful implementation of diagnostic reference levels, dosimetry in the clinical setup is a must. Physical measurement of the dose delivered to the patients undergoing diagnostic procedures is the first step in this direction and is achieved by measuring the dose delivered in the diagnostic procedures using dosimeters calibrated against a standard measuring system.
Owing to the increased demand for dosimetry measurements in diagnostic radiology, it is important that traceable calibration of instruments used in this field is provided. IEC 61267 and IAEA TRS 457 have recommended the establishment and use of reference beam qualities for the calibration of instruments used in diagnostic radiology.
Radiation Standards Section is recognised by International Atomic Energy Agency as a Secondary Standard Dosimetry Laboratory (SSDL) to provide dosimetry support to radiotherapy centres in India. SSDL-BARC has established standard reference beam qualities Radiation Qualities in Radiation ‘RQR’, Radiation Qualities based on Aluminium added filter ‘RQA’, Radiation Qualities based on Copper added filter ‘RQT’ and Radiation Qualities in Radiation beams for Mammography ‘RQR-M’ using Aluminium filters as recommended by IEC 61267 and IAEA TRS-457. RQR beam qualities are established for measurements to be carried out free in air and it does not include scattered radiation. RQA includes scattered radiations arising from the patients and RQT simulate the unattenuated beam used in CT with measurements done free in air. For mammography applications, one beam quality of RQR-M is simulated for Tungsten target.
ISO-4037 (ISO 4037: 1996(E), 1996) specifies four series of reference radiation for the calibration of protection level dosimeters where mean energy, resolution, homogeneity, typical air kerma rates and the additional filtration required to generate the beam qualities is specified. In the case of diagnostic beam qualities, IEC 61267/IAEA TRS 457 has recommended only the required half value layer (HVL) and homogeneity coefficient to generate beams. Additional filtration required to generate the beam qualities have to be determined for the X-ray machine used. In this paper, documentation of the methodology adopted in establishing the beam qualities in India is given.
Section snippets
Material and methods
Diagnostic beam qualities were established using an industrial X-ray machine, shown in Fig. 1, manufactured by YXLON International, Germany, model MG 325, 15-320 kV with a constant potential generator system. Table 1 gives the technical features of the X-ray machine.
X-ray beam is specified by its practical peak voltage, additional filtration, the half value layer and the homogeneity coefficient. Non-invasive technique was used to measure the Practical Peak Voltage (PPV) of the X-ray machine
Results and discussions
For the determination of the practical peak voltage, measurements using the Black Piranha was carried out at a distance of 66 cm from the focal spot of the X-ray machine. The X-ray meter was operated in the CT and mammography modes and measurements carried out with the X-ray machine current fixed at 2 mA. The practical peak voltage for the range (25kV-120kV) displayed agreed within ±1.4% of the measured value. The inaccuracy quoted by the manufacturer of the X-ray meter is ±1.5%. Table 2 gives
Conclusion
The present study on establishing diagnostic X-ray beam qualities will facilitate to disseminate air kerma quantity to the users in the field of diagnostic radiology. The work is the first step in the direction to establish diagnostic reference levels in the country.
The established diagnostic beam qualities RQR, RQA, RQT and RQR-M can be used to calibrate instruments which are used to characterise diagnostic X-ray machines. The beam qualities have conformed to IEC61267 and IAEA TRS457
Acknowledgment
Authors would like to thank Dr.Pradeep Kumar K.S, Associate Director, Health, Safety & Environment Group for his support and encouragement. Authors are also thankful to Ashish D Raut, Sachin P Bobade and Dipali Mhadeshwar for their help in arranging the setups and carrying out the experiments.
References (10)
Medical Diagnostic Equipment – Radiation Conditions for Use in the Determination of Characteristics
(2005)Medical Electrical Equipment - Dosimeters with Ionization Chambers And/or Semi-conductor Detectors as Used in X-Ray Diagnostic Imaging
(1997)Implementation of the International Code of Practice on Dosimetry in Diagnostic Radiology (TRS 457): Review of Test Results, Human Health Reports No. 4
(2011)X and Gamma Reference Radiation for Calibrating Dosimeters and Dose Rate Meters and for Determining Their Response as a Function of Photon Energy
(1996)Establishing IAEA TRS-457 diagnostic X-ray beam qualities at the Australian primary standard dosimetry laboratory
Australas. Phys. Eng. Sci. Med.
(2017)
Cited by (1)
Establishment and dissemination of radiological standards in the field of diagnostic radiology in India
2021, Journal of Medical Physics