SPECIFICATION. Kilovoltage X-ray calibration system for protection and diagnostic level dosimetry. Prepared by

Transcription

1 SPECIFICATION Kilovoltage X-ray Prepared by Igor Gomola, Technical Officer, Project ECU6023, Date 2015-Oct-06 Revision Date Status Comments Oct-06 Draft Igor Gomola Page 1 of 12

2 1. Scope This specification describes the main technical requirements for a kilovoltage X ray calibration system for calibration of equipment used in radiation protection and diagnostic radiology. The procurement of the system is planned for the Secondary Standards Dosimetry Laboratory (SSDL) of Ecuador in the framework of the IAEA Technical Cooperation project ECU6023. Expected outcome of this project is to upgrade calibration services for equipment used in radiation protection to end-users through the SSDL. 2. Applicable documents 1. INTERNATIONAL ATOMIC ENERGY AGENCY, "International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources", Safety Series No. 115, IAEA, Vienna (1996), 2. INTERNATIONAL ATOMIC ENERGY AGENCY, Calibration of Radiation Protection Monitoring Instruments, Safety Reports Series No. 16., IAEA Vienna (2000) 3. INTERNATIONAL ATOMIC ENERGY AGENCY, "Dosimetry in diagnostic radiology: An international code of practice", Technical Reports Series No. 457, IAEA, Vienna (2007), 4. INTERNATIONAL ATOMIC ENERGY AGENCY, "Implementation of the International Code of Practice on Dosimetry in Diagnostic Radiology (TRS 457): Review of Test Results", IAEA Human Health Reports No.4, IAEA, Vienna (2011), 5. INTERNATIONAL ELECTROTECHNICAL COMMISSION, Medical diagnostic X-ray equipment - Radiation conditions for use in the determination of characteristics, IEC 61267, Geneva, Switzerland INTERNATIONAL ORGANIZATION FOR STANDARDIZATION, X and gamma reference radiation for calibrating dosimeters and dose rate meters and for determining their response as a function of photon energy, ISO, Geneva, ISO 4037 (1999) 7. The Consultative Committee for Standards of Ionizing Radiations (CCRI), X-ray beam qualities, Bureau International des Poids et Mesures (BIPM), 3. Abbreviations SSDL: HVL: SDD: FS: CBA: Secondary Standards Dosimetry Laboratory of Ecuador Half Value Layer Source to detector distance Field Size Diameter Central Beam Axis Page 2 of 12

3 4. Requirements 4.1. Functional requirements. The new X ray calibration system shall be able to produce desired radiation beam qualities for calibration of equipment used in radiation protection (narrow spectrum series) and diagnostic radiology (conventional diagnostic beams, except mammography). The calibrations benches are already available at the SSDL, for this reason is important to integrate the existing benches with new kv calibration system Performance requirements All performance specifications and tests shall conform to the relevant standards of the IAEA, IEC and ISO, as specified above Technical specification The X ray calibration system shall include the following components: 4.3. Technical specification The X ray calibration system shall include the following components: X ray tube with HV cables with W anode, for (i) diagnostic, (ii) protection level Shielding cabinet for X ray tube assembly High voltage generator System control panel Beam shutter Beam collimation system Filter assembly HVL (Half Value Layer) measurement system Ancillary eqquipment Safety items X ray tube with HV cables Metal ceramic X ray tube X ray tube voltage range, at least: 20 kv kv Continuous rating power at least 3 kw Target material: Tungsten Thickness of the exit window: max 1 mm Material of the exit window: Beryllium Anode angle: at least 20 degrees Focal spot size: at least 4 mm Cooling medium: preferably water Shielding cabinet Page 3 of 12

4 The shielding cabinet shall (i) totally enclose X ray tube with the shutter and cables (ii) provide mechanical support for the remote controlled filter changing device The enclosure shall have a door to access the tubes and the shutter The enclosure door shall be with an interlock that disables the power when opened The shielding cabinet surrounding X ray tube shall provide sufficient shielding from the scatter and leakage-radiation created by the X ray tube in use The design shall ensure that the leakage radiation complies with the International Basic Safety Standards [1] The X ray tube head shall be mounted in a holder allowing geometrical alignment with desired central radiation beam axis (CBA) The height of CBA above the floor level shall be 110 cm High voltage generator Unipolar system, high frequency, constant potential type, the ripple less than 0.5% Output voltage range, at least: 20kV kv (0.1 kv steps). The accuracy of the high voltage shall be better than ± 1% and the repeatability better than 0.05 kv Output current, at least: from 0.5 ma to 40 ma (possible to change in 0.1 ma steps). The accuracy of the current shall be better than ± 1% and the repeatability better than 0.05 ma Output power (at least): 3kW The performance of the generator shall not be affected by ± 10 % fluctuation of the mains input voltage The HV generator shall operate at mains input 110 V single phase (available power line conditions to be confirmed by the counterpart in advance) Cooling unit for X ray system shall have sufficient capacity to allow safe and stable operation of X ray unit at maximum power for several hours. The cooling unit with close circuit for the cooling medium is preferable X ray control panel Preselection of high voltage in steps of 0.1 kv Display actual value of HV (at least 3 digits) Preselection of tube current in steps of 0.1 ma Display actual value of current (at least 3 digits) Preselection of exposure time in steps of 1 sec Display actual value of exposure time (at least 5 digits) Remote control of the beam shutter (On/Off) by selected exposure time Memory for setup of X ray tube parameters Digitally assigned limit data (high voltage, current, anode power dissipation) Warm up programme for X ray tube (manual and automatic mode) Warm up history Emergency stop button Indication X ray beam Off/On Connection to various safety interlocks (door switch, door eye beam, radiation monitor signal) to avoid unintended exposure of staff Page 4 of 12

5 As an option, the control unit shall be equipped with a PC interface allowing remote control X ray beam shutter A shutter shall be mounted inside the shielding cabinet in the front of the exit window of the X ray tube (preferably behind the primary collimator) The shutter must be thick enough to attenuate the transmitted air kerma rate of the primary radiation beam to 0.1% on the CBA for the radiation quality with the highest mean energy The shutter shall be remotely controlled from the X ray control panel The actual shutter status (Open/Close) shall be indicated on the control panel The shutter transit time shall be less than 100 msec The actual value of the shutter transit time together with its uncertainty (Δt, %SD(Δt)) shall be measured in the factory. The report from the measurement shall be provided to the end-user Beam collimation system Primary collimation system shall be made preferably from tungsten in the shape of a conical aperture, which is positioned between the X ray output window and the beam shutter Secondary collimation system is used to define a reference filed size at the given calibration conditions. The secondary collimator shall be placed between the filter assembly and the monitor chamber The diameter of the second conical aperture (collimator) determines the field size at the reference point. There shall be provided a set of easily exchanged collimators with various diameters to obtain field sizes matching various irradiation conditions. At least, the following irradiation conditions shall be possible set-up SDD=200 cm, FS=30 cm SDD=100 cm, FS=10 cm HVL measurements: SDD=100 cm, FS=5 cm The design shall allow easy exchange of the secondary collimators with no need to dismount a monitor chamber Behind the secondary collimation system shall be placed a rigid holder for mounting a monitor ionization chamber (e.g. PTW type 34014). The geometrical centre of the monitoring chamber shall be positioned in the central radiation beam axis Behind the monitor chamber shall be placed the third conical aperture with diameter bigger than radiation field size. The purpose of this aperture is to reduce backscatter radiation The distance between the focal spot of the X ray tube and the end point of the third aperture shall not exceed 40 cm Page 5 of 12

6 Filter assembly The filter assembly is used to modify the photon spectrum of radiation beams produced by the X ray tube to meet the characteristics of radiation beam qualities required for calibration of equipment A set of metal filters shall be provided to produce desired radiation beam qualities characterized by 1 st HVL, as described in Tables 1, 3, 4 and The metal filters (Al, Cu, Pb, Sn) used for the establishment of required radiation beam qualities shall have certified purity of 99.9%, at least The metal filters for all beam qualities shall be placed in removable and remotely controlled carrousels It shall be possible to remotely change filter wheel position to get the required filtration within each series (N series, RQR, RQA, RQT series). It means, for example, that changing the filters to the desired position during the calibration with RQA series (2,3,4,5,6,7,8,9,10) shall be done remotely without need to enter the irradiation room The carrousel to be constructed as a rotational disk with several holes located between the centre of the disk and the radius All holes in the disk shall have the same diameter and shall be designed to hold the metal filters. Each radiation beam quality may require combination of various metal filters therefore the each hole shall allow to install more than one metal filter (see Appendix 1 and 2) The each hole and the each disk shall be uniquely coded to assure correct setup of selected filters during calibration The metal filter (beam code) selected during the irradiation shall be indicated in the control panel of the device The carrousel shall be mounted between the shutter and the secondary collimation system in a way that the centre of the holes in the disk is on the CBA On the radiation beam axis (between the X ray tube output and the primary collimator) shall be included manual or automatic filter insert system allowing to add additional filters into the beam (i.e. N series above 40 kv require inherent filtration adjusted to 4 mm of Aluminium, see Table 1, Appendix 1) The thickness of added filtrations given in Tables 1, 3, 4, 5, are representing the nominal values and shall be adjusted individually with the given X ray tube to obtain desired HVL values within required tolerances [5, 6] HVL measurement system Manual insert system including removable attenuators (sheets of various metals) shall be possible to place on the calibration bench. The centre of the metal sheets shall be located on CBA The minimum distance from the focus of the X ray tube to the position of removable attenuators shall be 50 cm The desired thickness of the attenuator is adjusted by adding different thicknesses of attenuating material until the required attenuation of radiation beam is achieved The set shall include aluminium and copper sheets made of various thicknesses to determine the desired HVLs Each metal filter shall be accompanied with a certificate stating (i) purity of the material (ii) thickness, including the measurement uncertainty The required purity of the material used for attenuation shall be at least % The collimator assuring narrow beam geometry required for measurement of HVLs shall be included Page 6 of 12

7 Optionally, automatic HVL measurement system shall be offered. In this case, the change of filter material thicknesses is remotely controlled so the full set of measurements is performed without entering the irradiation room Ancillary equipment Spare parts and tools used for on-site preventive maintenance of X ray system. More details are required. Spare part and tools list shall be provided Safety items Radiation monitor for workplace monitoring to be installed in the calibration room. The display shall be located outside of the irradiation room (in the control room) and indicate radiation exposure in terms of Sv/hr. A visual and audible alarm signals shall be initiated, when the radiation source is in the irradiation position (exposure rate in the irradiation room is elevated) Video color surveillance system: 2 cameras with wide-angle lenses and wall mounts (each camera to survey 2/3 of the irradiation room) and 2 monitors located in the control room The X ray system shall be connected to the radiation safety infrastructure already installed in the irradiation and control room (see Appendix 3). 5. Accompanying documents 5.1. Performance specifications 5.2. Operating instructions 5.3. Installation instructions 5.4. Preventive maintenance manual 5.5. Service manual with schematic circuit diagrams of electronic circuits of the X ray system 5.6. Installation requirements 5.7. Acceptance testing protocol 6. Marking The X ray system shall have the safety marking as required by international standards given in section 2 Applicable documents. 7. Packing The X ray calibration system shall be packed in accordance with international standards that are applicable for the shipment of this type of equipment. 8. Installation The Contractor shall install and test the X ray calibration system at the SSDL of Ecuador 9. Testing (Factory and Site) and Acceptance 9.1. The X ray calibration system shall be tested in the factory before the shipment (FAT - Factory Acceptance Testing) to assure that the system is in working conditions and fulfil all technical requirements. The FAT results shall be submitted to the IAEA (attn. to Technical Officer of the TC project) before shipping the system to end user. The FAT results shall include at least the following parameters: - radiation beam profiles for all collimators measured at the distance of 1 m with at least one beam quality energy Page 7 of 12

8 - radiation beam output in terms of air kerma rate (mgy/min) measured on CBA at the distance of 1m with at least one beam quality per beam series (i.e. N100, RQR5, RQA5, RQT9). The used kv x ma shall be close to 1.5 kw. - air kerma vs irradiation time (1 sec 60 sec range ) for selected beam quality to verify shutter functionality 9.2. The X ray calibration system shall be tested after installation at the SSDL in accordance with the applicable standards mentioned in chapter 2 by the Contractor together with the staff of the SSDL to demonstrate that: the performance meets the manufacturer s performance specifications and the minimum requirements specified herein as determined by the IAEA the functionalities of the whole system is maintained 9.3. The results of the testing of the X ray calibration system shall be documented by the Contractor in Acceptance Protocol that shall be signed by the representative of the SSDL 10. Training The Contractor shall provide the training in the operation and first line maintenance of the X ray calibration system at the SSDL of Ecuador immediately after the installation. Type of training with the detailed program and expected duration shall be provided. 11. Warranty and service A complete warranty shall be offered for at least 1 year, starting after formal acceptance testing Time of installation, included all the requirements shall be provided Local or regional representation for services shall be provided, CV of the local/ regional representations, answer time, type of penalties in case of no complies shall be provided An option for maintenance contract (starting after the warranty period) shall also be included in the offer Training for in-house engineers on first line maintenance The Contractor shall guarantee that replacement parts are available for at least 10 years after installation of the X ray calibration system The Contractor shall ensure that service support and further upgrades of the system are available As an option, a proposal for service training shall be included in the offer. Page 8 of 12

9 APPENDIX 1 BEAM QUALITIES FOR PROTECTION LEVEL CALIBRATIONS Table 1. Characteristics of narrow-spectrum series ISO-4037 [6]. The minimum range of established beam qualities for the SSDL is in the range from N40 to N200 Page 9 of 12

10 APPENDIX 2 BEAM QUALITIES FOR DIAGNOSTIC LEVEL CALIBRATIONS TABLE 2. RADIATION QUALITIES FOR CALIBRATIONS OF DIAGNOSTIC DOSIMETERS (IAEA TRS- 457) Radiation quality RQR Radiation origin Radiation beam emerging from X ray assembly Material of an additional filter no phantom Application General radiography, fluoroscopy and dental applications (measurements free in air) RQA Radiation beam with an added filter Aluminum Measurements behind the patient (on the image intensifier) RQT Radiation beam with an added filter Copper CT applications (measurements free in air) TABLE 3. CHARACTERIZATION OF RADIATION QUALITY SERIES RQR Radiation quality X ray tube voltage **Added filtration Nominal 1 st HVL (kv) (mm Al) (mm Al) RQR RQR RQR RQR 5* RQR RQR RQR RQR RQR *This value is generally selected as the reference radiation quality for non-attenuated beams for general radiography applications. ** The fixed filtration consists of 1.0 mm Be + monitor chamber. The values of added filtration are informative only and shall be adjusted to achieve desired HVL values within ± 5%. Page 10 of 12

11 APPENDIX 2 CONTD. BEAM QUALITIES FOR DIAGNOSTIC LEVEL CALIBRATIONS TABLE 4. CHARACTERIZATION OF RADIATION QUALITIES SERIES RQA Radiation quality X ray tube voltage **Added filtration (kv) (mm Al) (mm Al) Nominal 1 st HVL RQA 2 40 RQR RQA 3 50 RQR RQA 4 60 RQR RQA 5* 70 RQR RQA 6 80 RQR RQA 7 90 RQR RQA RQR RQA RQR RQA RQR *This value is generally selected as the reference radiation quality for attenuated beams for general radiography applications. ** The fixed filtration consists of 1.0 mm Be + monitor chamber. The values of added filtration are informative only and shall be adjusted to achieve desired HVL values within ± 5%. TABLE 5. CHARACTERIZATION OF RADIATION QUALITY SERIES RQT Radiation quality X ray tube voltage Added filtration Nominal 1 st HVL (kv) (mm Cu) (mm Al) RQT RQR RQT 9* 120 RQR RQT RQR *This value is generally selected as the reference radiation quality for computed tomography. ** The fixed filtration consists of 1.0 mm Be + monitor chamber. The values of added filtration are informative only and shall be adjusted to achieve desired HVL values within ± 5%. Page 11 of 12

12 APPENDIX 3 Layout of the premises at the SSDL of Ecuador Fig.1 Current X-ray system installed at the SSDL of Ecuador Fig.2 X-ray and gamma calibration room at the SSDL of Ecuador Page 12 of 12