1. MAIN FEATURES FOR CALIBRATING DOSEMETERS ORAMED WP5 J.-M. Bordy Laboratoire National Henri Becquerel (CEA/LIST/LNHB), France ORAMED 2011 January 2011

2. 2/16 INTRODUCTION : Depending on the radiation type, photons, beta particles and neutrons, the International Organisation for Standardization (ISO) has published 4 series of standards giving information on (i) the radiation qualities to be used for type test and calibration, (ii) the methods for establishing primary standards and (iii) for calibrating dosemeters in these radiation beams/fields. Those standards are ISO 4037, 6980, 8925 and 12789 for photons beta particles and neutrons respectively. The statements gathered in the following slides are based on those standards. They present advices to help laboratories in performing good calibrations. Here are also presented (i) some features included in ISO DIS 29661 which changes a few points, such as the reference point for personal dosemeters, and (ii) ORAMED proposals for eyes lens dosimetry (in both cases, changes are specially marked).

3. 3/16 DEFINITIONS 1/3 Type Test: Before being available on the market, dosimetry systems are type tested. Type tests are intended to demonstrate the basic performance of the type of the dosemeter. To help the user in choosing his dosemeter depending on the workplace Calibration: When the dosimetry system is used by dosimetry services, it’s calibration MUST be traceable to the international system of units through national or international references (both national and international references being at the same level in the metrological chain).

4. 4/16 DEFINITIONS 2/3 Radiation qualities: Photons: from a few keV to 10 MeV using low and medium X rays, radionuclide sources, high energy accelerator and pool reactor. Beta particles: based on radionuclide sources Neutrons: based on radionuclide sources, accelerators providing quite mono energetic beams and when additional equipments are used “realistic radiation fields” mimicking the radiation fields at workplace. Phantoms: Irradiation of dosemeters are done accordingly to the conditions of use: i.e. free in air for area dosemeters (that means without any scattering material in the radiation field to avoid perturbations), and on phantom for individual dosemeters (the phantom shape and dimensions depend on the wearing condition, on the trunk (slab) and wrist, finger, head (cylinder of different diameters). The “head” phantom has been proposed by ORAMED WP2 as a right cylinder of 20 cm diameter.

5. 5/16 DEFINITIONS 3/3 Point of test in a radiation beam/field: point in the radiation field at which the conventional quantity value is known Reference point of a dosemeter (plot in red on the scheme): point of the dosemeter that is placed at the point of test for calibration and test purposes. Ideally, this point must be stated accordingly to the specification of the manufacturer or in the absence of information chosen by the calibration or testing laboratory and stated on the certificate containing the results. ISO DIS 29661: For personal dosemeters, the reference point, of any personal dosemeter, is at the centre of the front surface of the phantom behind the dosemeter. The personal dosemeter is put on the phantom such that the reference direction of the dosemeter through its geometrical centre hits the reference point

6. 6/16 Calibration coefficient, N, for a radiation quality U and an angle  1/2 conventional quantity value of the dose equivalent at the point of test corrected indication of the dosemeter correction factor for non-constant response (i.e. linearity) correction summands (i.e. background) correction factors (i.e. ambient condition, temperature, pressure, hygrometry … ) indication of the dosemeter

7. 7/16 Calibration coefficient, N, for a radiation quality U and an angle  2/2 The conventional quantity value can be obtained through a secondary or working standard or a monitor device traceable to a primary standard or directly from the primary standard as shown below. Primary quantity : Air kerma Absorbed dose to tissue Fluence Radiation type : photon beta particle neutron Conversion coefficients (values and associated uncertainties for radiation qualities are given in ISO standards) H p (0.07,  ) H p (10,  ) H*(10) H ’(0.07,  )  If irradiation of the standard, realized as a measuring device, and the dosemeter to be calibrated are performed simultaneously, it must be verified that the indication of one instrument is not influenced by the presence of the other one in the beam).

8. 8/16 Irradiation set up for a personal dosemeter (example of whole body dosimetry) Personal dosemeter Reference point ISO water Slab phantom Direction of radiation incidence Build up layer If required Build up layer If required Reference direction  Reference point  Present situation ISO DIS 29661 D: Distance from the effective emission point of the source D D Reference direction

9. 9/16 The choice of the distance between the source and the point of reference can be a compromise between several parameters, e.g., the geometry of the irradiation facility, the field homogeneity, the dose rate, backscatter radiation from the room walls, etc. It must be pointed out that the whole surface of the phantom has to be exposed to radiation for personal dosemeter and the whole area dosemeter must be exposed too. If not a correction factor could be necessary. Positioning of a whole-body dosemeter at the slab phantom surface Reference point ISO DIS 29661 Reference point ISO DIS 29661 Reference point Present situation Personal dosemeter Personal dosemeter Phantom Stand Spacer D D D D

10. 10/16 Free in air Slab phantom cylindrical phantoms Simultaneous irradiation of several dosemeter (front view) Before the simultaneous irradiation is adopted, it shall be verified that it leads to results identical to or with only small deviations of those obtained when only one dosemeter is irradiated free in air or on the phantom. The amount of deviation deemed acceptable depends on the level of accuracy required. Some effects require additional attention: homogeneity of the radiation field, scattered and attenuation of radiation from adjacent dosemeters.

11. 11/16 Influence quantityReference condition Standard test condition (unless otherwise indicated) Radiation energy (Radiation quality)Stated conditions 1) As reference condition Direction of radiation incidenceStated direction 1) Stated direction  5° Dose equivalent rate for dose equivalent measurements Stated dose rate 1) Stated dose rate  10° Natural radiation background Ambient dose equivalent rate as low as possible but always lower than 0,1 µSv/h Ambient dose equivalent rate of 0,2 µSv/h or less if practical Contamination by radioactive materialNegligible Climate (ambient temperature and relative humidity) + 20 C 50 % +15 C to + 30 C 2) 30 % to 75 % 2) Atmospheric pressure 3) 101,3 kPa86 kPa to 106 kPa Electromagnetic field of external originNegligible Less than the lowest value that causes interference 1) The stated condition shall be contained in the rated range of the dosemeter under test. 2) The actual values of these quantities at the time of test shall be stated. The values in this table are intended for calibrations or tests performed in temperate climates. In other climates, it may be permitted to exceed the ranges of standard test conditions beyond those stated in this table, where instruments are to be used in these climates. 3) In general the atmospheric pressure is uncontrollable. If, in special cases, the measurements can be performed only at an atmos­ pheric pressure beyond the range of the standard test condition, the calibration factor shall be corrected when it deviates signifi­ cantly from its value under reference conditions. In practice, the target uncertainty services as the criterion for accounting for an influence quantity by an explicit correction or for incorporating the effect into the uncertainty. List of reference conditions and standard test conditions (from ISO DIS 29661). If no statement for an influence quantity is given in the table below, the reference and standard test condition shall be stated by the manufacturer of the dosemeter or shall be fixed by the calibration or testing laboratory.

12. 12/16 Summary of some statements following the ORAMED conclusions (1/2). Type test and calibration of APDs: Up to know there is no standard presenting special requirements for the type test and the calibration of APDs in pulsed radiation beams representative of the radiation fields met at workplace i.e. in interventional radiology and cardiology. It is advisable to write such a standard. This standard shall include type test allowing to demonstrate that the dosemeters are able to correctly measure operational quantities in high instantaneous pulsed dose rate and pulse frequency such as those that can be met at workplace in interventional radiology and cardiology. (see ref of WP3 guide line) Basically the calibration of APDs for using them in pulsed radiation fields follows the same rules as for using them in industry. Use of the same phantoms, same positioning on the phantom, etc …As for any application, when it is possible, it is advisable to calibrate the dosemeter in a radiation beams having characteristics close to the one in which it will be used, specially if the variation of the response in terms of energy or linearity do not properly cover the range in which the dosemeter will be used. Thus calibration should be done in pulsed radiation beam accordingly to the characteristics of the radiation field at work place. The choice of the calibration radiation beam(s) must be done in agreement between the calibration laboratory and the users.

13. 13/16 Typical radiation fields met in IR/IC ParameterRange High voltage60-120 kVp Intensity5-1000 mA Inherent Al equivalent filtration4.5 mm Additional Cu filtration0.2 – 0.9 mm Pulse duration1 - 20 ms Pulse frequency1 – 30 s -1 Dose equivalent rate in the direct beam (table) 2 to 360 Sv.h -1 Dose equivalent rate in the scattered beam (operator – above the lead apron) 5.10 -3 to 10 Sv.h -1 Energy range of scattered spectra20 keV – 100 keV

14. 14/16 Summary of some statements following the ORAMED conclusions (2/2). Eyes lens dosimetry: As it has been mentioned previously, ORAMED proposed to add a new phantom to the ones already included by ISO in its standard and ICRU in its report. This phantom has a shape closer to the shape of the head, it is a right cylinder with 20 cm diameter.  To calculate the conversion coefficients from primary quantities to the operational quantity H p (3) the phantom is made of the 4 elements ICRU tissue.  For calibration purposes, the phantom is a PMMA can having the same dimensions and filled with water. Dosemeters must be fixed on its surface following the same rules as the one written in above mentioned ISO standard. Use of extremity dosemeters in nuclear medicine: Because both photon and beta radiations can be met at workplace, even if the main component of the radiation field is due to photons, dosemeters have to fulfil the requirement of the type test for beta radiations.

15. 15/16 Angle (degree)W 60W 80W 110W 150 01.471.581.651.57 201.461.581.631.54 451.421.531.601.54 601.341.471.541.50 751.201.341.451.40 Resolution % (keV) 48 (29) 55 (44) 51 (56) 56 (84) Monte Carlo calculations (PENELOPE Code), standard uncertainties better than 0.3% Angle (degree) IEC 61267ISO 4037 RQR4 (60 kV)RQR7 (90 kV)RQR9 (120 kV)N30N80N120 01.2391.3761.4611.0191.6651.588 201.2291.3731.4521.0091.6591.584 451.1791.3261.4060.9551.5991.554 601.1081.2531.3470.8751.5461.516 750.9531.1071.2100.6981.4201.424 Resolution % (keV) 73 (27)67 (32)77 (44)32% 27%

16. 16/16 ISO 29661 will reached the last step before being published in next April. It will be published at the beginning of 2012. The possibility of using a phantom like the one proposed by ORAMED WG 2 for calibrating eye lens dosemeters is already mentioned in ISO standards 12794 and ISO DIS 29661 The presentation of the results of a calibration must follow the requirement of ISO 17025 the uncertainty budget must be evaluated following the method presented in the GUM (ISO/IEC guide 98-3:2008) CONCLUSIONS

17. 17/16 ISO 4037 International Organization for Standardization, X and gamma referenceradiations for calibrating dosemeters and dose rate meters and for determiningtheir response as a function of photon energy, Part 3: Calibration of area and personal dosemeters and the measurement of their response as a function of energy and angle of incidence. ISO 4037-3. (ISO: Geneva) (1993). ISO 6980 International Organization for Standardization, reference beta-particle radiation, Part 3: Calibration of area and personal dosemeters and the measurement of their response as a function of beat radiation energy and angle of incidence. ISO 6980-3. (ISO: Geneva) (2007). ISO 8529 International Organization for Standardization Reference neutron radiation, Part 3: Calibration of area and personal dosemeters and the determination of their response as a function of neutron energy and angle of incidence. ISO 8529-3. (ISO: Geneva) (1996). ISO 12789 International Organization for Standardization Reference neutron radiation, Part 2: Calibration fundamentals related to the basic quantities characterising simulated workplace neutron fields. ISO 12789-2. (ISO: Geneva) (2005). ISO 12794 International Organization for Standardization, Individual thermoluminescence dosemeters for extremities and eyes, ISO 12794 (ISO: Geneva) (2000) ISO DIS 29661 International Organization for Standardization, reference radiation fields for radiation protection – definition and fundamentals concepts. To be published in 2012. IEC 61267 standard « medical diagnostic X-ray equipment – Radiation conditions for use in the determination of characteristics » ISO 17025 International Organization for Standardization, General requirements for the competence of testing and calibration laboratories, ISO 17025 (ISO: Geneva) (2005) GUM (ISO/IEC guide 98-3:2008) ORAMED 2011, Radiation Measurement special issue, 2012 A few « papers » to read