Equine scintigraphy : assessrnent of the dose - PDF Document

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  1. D01: IO. 105 l/radiopro:2003001 Radioprotection 2003 Vol. 38, no 1, pages 61 i 73 Technical note Equine scintigraphy : assessrnent of the dose received by the personnel J.-F. BOTTOLLIER-DEPOIS ’, F. TROMPIER~ 1. CLAIRANDI, (MuriLiscript recrivrd 12 July 2002, nccrptrd 14 Novemhrr 2002) ABSTRACT Following a request from the Permanent Secretary of the French Commission for Artificial Radiodement3 (CIREA) engaged to investigate a request for a licence related to a new scintigraphy unit dedicated to equidae, a dosimetric assessment concerning the personnel attending the examination was carried out. This scintigraphy unit depends on the Goustranville Centre for lmaging and Research on the Locomotive Diseases of Equidae (CIRALE) in the Calvados region. The dosimetric assessment was carried out for the different operators during the successive stages of the scintigraphic examination. Assuming 150 examinations per year, the annual equivalent dose to the fingers skin is 150 mSv maximum for the technologist and 2 mSv for the veterinary surgeon; the annual effective dose ranges from 0.15 to 0.45 mSv, depending on the operators. RÉSUMÉ Scintigraphie équine : estimation de la dose reçue par le personnel. Suite à une demande du Secrétariat permanent de la Commission interministérielle des radioéléments artificiels (CIREA) amené à instruire une demande d’autorisation relative a une nouvelle installation dédiée à la scintigraphie équine, une évalualion dosimétrique concernant le personnel présent lors de l’examen a été réalisée. Cette installation dépend du Centre d’imagerie et de recherche sur les affections locomotrices des équidés (CIRALE) situé à Goustranville dans le Calvados. L’évaluation dosimétrique a été réalisée pour les différents opérateurs au cours des étapes successives de l’examen scintigraphique. En prenant l’hypothèse de 150 examens par an, l’équivalent de dose annuel i la peau des doigts est au maximum de 150 mSv pour le manipulateur et de 2 mSv pour le vétérinaire ; la dose efficace annuelle est quant à elle comprise entre 0,15 et 0,45 mSv selon les opérateurs. 1. Introduction Following a request from the Permanent Secretary of the CIREA engaged to investigate a request for a licence related to a new scintigraphy unit for equidae, a dosimetric assessment conceming the personnel attending the examination was carried out. The operation took place on March 13, 2001. This scintigraphy unit depends on the Goustranville Centre for Imaging and Research on the Locomotive Diseases of Equidae (CLRALE) in the Calvados region. ‘ l’rance. IRSN. D6partemerit de proteciion de la santé de I’hominc et de dosimitrie, B.P. 17, 92262 Fontenay-aux-Koses Cedex, RADIOPROTECTION - VOL. 18 ~0 EDP Sciences, 2003 hl Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro

  2. 1. CLAIRAND et al. The scintigraphic examination operated in CIRALE is skeletal scintigraphy, the most commonly performed equine nuclear medicine procedure. Skeletal scintigraphy (Hoskinson, 2001 ) offers high sensitivity for detecting diseases of the locomotive system of the horse causing Iameness or poor performance. The injuries sought relate to the bones (fractures, cracks, over-strained sub-chondral osteolysis), the joints (degenerative, traumatic, septic diseases) and the soft tissues (muscles, tendons, ligaments). This scintigraphic examination involves the intravenous injection of a phosphonate compound usually radiolabeled with technetium-99m (99mTc), and subsequent imaging of the distribution of radioactivity within the animal. 99mTc is pure gamma emitter with energy of 140.5 keV and half-life of 6 hours. To perform this type of examination on a horse weighing 400 to 600 kg, the activity of 99mTc administered is usually 4 to 6 GBq (10 MBq kg-’), which is 6 to 8 times higher than the activity commonly used for a human bone scintigraphy which is around 0.7 GBq for a standard adult (Gambini and Granier, 1997). The radiopharmaceutical used here is ”“‘Te-labeled diphosphonate (”mTc-DPD). The day of the operation 4.4 GBq of 99mTc-DPD were administered intraveneously to the external jugular vein of the horse after tïtting a catheter. dicarboxypropane The scintigraphic examination, carried out using a dedicated gamma camera, comprises two acquisition phases. The first phase, known as the “vascular and soft tissue phase”, takes place 15 minutes after injection of the radiopharmaceutical and enables viewing blood vessels and soft tissues. The second phase, known as the “bone phase”, takes place 3 hours after the injection and enables the bones and the joints to be displayed. The duration of each phase may Vary from approximately 10 minutes to 1 hour depending on the aim of the examination and the movements of the horse. Hereinafter, the first and second phases that make up the same scintigraphic examination are respectively noted “phase 1 ” and “phase2”. Between these two phases and during the 48 hours following the examination, the horse remains in a stall situated in an outside building. The examination is marked by several stages during which the personnel is likely to be exposed to the radiation emitted by the 99mTc. These stages are, in chronological order: 1. preparation of the radiopharmaceutical in the preparation laboratory under a fume hood equipped with lead glass Shields, 2. injection of the radiopharmaceutical at time T (Fig. I), 3. phase 1 at T + 15 min (Fig. 2), 4. leading of the horse from the examination room to its stall, 5. waiting phase during which the horse remains in its stall, RADlOPROTECTION - VOL. 38 ~ N” 1 (2003) 62 Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro

  3. EQUINE SCINTIGRAF'HY ASSESSMENT OF THE DOSE RECEIVED BY THE PERSONNEL Figure 1 - Intravenous injection of the radiopharmaceutical (99mTc-DPD). Injeclion intraveineuse du radiopharmaceutique Pym Tc-DPD). Figure 2 -Phase 1 o f fhe sciniigraphic examinution. Phase 1 de I'euirnen sciniigraphique. 63 ~ VOL. 38 - N" 1 (2001) RADIOPROTECTION Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro

  4. 1. CLAIRAND P I ul. TABLE I Details of the successive stages of the scintigraphic examination. Caractéristiques des étapes successives de l’examen scintigraphique. Fume hood with lead Stage 1 Preparution of /tir radioplirirmaceuiir.u/ T 15 Preparation of the radiophdrmaceutical glass shield Tungsien ayringe shield Plicrs, etc. Sbge 3 Phase 1 (rascular and soft tis.sue phrwe) Gamniü-cainera operation T Lead scrccn, distance 1s V Positioning of the horse Lead glovea, distance Rigid Icading rein ( 1 m) L a d glovea, lead screen S Oc Ihe Movemenr of accessories Stage 7 Pha.w 2 (hune phase) w Lead scrmn, disiüncç A 45 Stage 5 Waii hetween p h u w ~ l I 180 I (the horw wnuirns in i i ~ (*) T tcchnologi\t, V vetennary rurgeon, S stall lad, A a\ai\tdnt 6. leading of the horse from the stall to the examination room, 7. phase 2 at T + 3 hours, 8. leading of the horse to its stall where it remains for 48 hours. The contaminated loose straw is removed at least 5 days after the examination and is stored in a dedicated place for decay during several months. Four persons are present during the examination: the technologisi, the veterinary surgeon, the stall lad and the assistant. Each operator wears at least latex gloves, a 0.5 mm thick lead apron and a thyroid shield. Table 1 details each stage RADIOPROTECTION ~ VOL. 38 ~ N” 1 (203) 64 Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro

  5. EQUINE SCINTIGRAPHY: ASSESSMENT OF THE DOSE RECEIVED BY THE PERSONNE1 (from 1. to 8.) of the scintigraphic examination, specifying its duration, the role of each operator and the additional radiological protection for certain operators. This article presents the results of the study camed out by the TRSN, which consisted in assessing the dose received by the personnel based on measurements performed on site during the successive stages of the equine scintigraphic examination. 2. Material and methods This study consisted in canying out a spectrometric analysis of the gamma radia- tion, measurements of the dose to the fingers and to the whole body of the person- nel exposed, and measurements of dose rate in air. The personal dosimetry and the determination of the dose rate in air were performed by assessing the operational quantities Hp(0.07), Hp(l0) and H*( IO), as defined by the International Commis- sion on Radiological Protection (TCRP, 199 1) and by the International Commis- sion on Radiation Units and Measurements (ICRU, 1992). The quantities Hp(0.07) and Hp( 1 O) correspond to the personal dose equivalent respectively for 0.07 mm and 10 mm in depth and the quantity H*( 1 O) corresponds to the ambient dose equivalent. The dosimetric assessment was carried out under normal operating conditions, that is, the risk of accidental contamination was not taken into account given the measures implemented for packaging and handling of the radionuclide. 2.1. Spectrometric analysis Spectrometric analysis of the gamma radiation emitted by the 99mTc was made using a nanoSPECTM spectrometer (Target) consisting of a scintillator (NaI(T1)) connected to a multi-Channel analyser. Spectrum acquisition was performed in the nearby environment of the injected horse first in the examination room with and without a lead protection screen and second, at the entrance to the stall where the horse remains when the acquisition phases of the scintigraphy examination are not being carried out (Fig. 3). The aim of this measurement was to obtain the spectrum shape and to determine the average energy of the photons in order to make sure of the good response from certain dosemeters that may depend on the energy. 2.2. Persona1 dosimetry Several types of personal dosemeters were fitted to the operators throughout the ex.amination. The dose to the fingers was determined using passive thermoluminescent detectors (TLDs) consisting of lithium fluoride (FLi), calibrated in terms of kerma in the tissue (kermatiSsu). These TLDs were fitted onto the thumb and index finger of each hand (over the latex gloves, under the lead RADIOPROTECTION ~ VOL. 38 ~ No I (2003) 65 Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro

  6. 1. CLAIRAND eral. Figure 3 - Measurement of the m e r , spectrurn af staIl enb-ance, using ihe nanoSPECT'" (TurgetJ specfrometer. Mesure du specfre en énergie à l'entrée du box ù l'aide du specfromèfre nanoSPECM (Target). gloves when the operators wear them) for the veterinary surgeon and the technologist. In addition, active electronic dosemeters. calihrated in terms of Hp(lO), of type DOSICARDTM (Eunsys Mesures), EPDTM (Siemens), Stephen- 6000TM (Stephen) were fitted onto the chest of the four operators. The technologist and the vetennary surgeon were weanng a DOSICARDTM and an EPDTM over the lead apron and a DOSICARDTM under the lead apron; the stall lad and the assistant were each wearing a Ste~hen-6000~~ DOSICARDTM dosemeter under the apron. The values of Hp(l0) indicated on the electronic dosemeters were recorded at the end of phase 1 and phase 2. dosemeter over the apron and a 2.3. Ambient dose equivalent rates Amhient dose equivalent rates were measured during each stage of the examination, in the preparation laboratory, in near proximity (0.5 m, 1 m and 2 m) RADIOPROTECTION - VOL. 38 ~ N" 1 (2003) 66 Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro

  7. EQUINE SCINTIGRAPHY: ASSESSMENT OF THE DOSE RECEIVED BY THE PERSONNEL hindquarters \ bladder rear Figure 4 - Points of measurements for the ambient dose equivalent rates H*(lO). Points de mesure des débits d’équivalent de dose ambiant H*(lO). and in contact with the injected horse at several specific anatomical locations (Fig. 4) using two radiation monitors 6150 AD 6 (Befic/Saphymo), calibrated in terms of H*( 10). 3. Results 3.1. Specîrometnc analysis Figure 5 shows three gamma fluence spectra collected near to the injected horse first in the examination room behind a lead screen, second in the examination room without lead protection and last in the stall in which the horse remains. The number of pulses per Channel has been normalized to 1 for the energy of the photon emitted by the 99mTc, i.e. 140.5 keV. The analysis of the gamma spectra first of al1 reveals a large proportion of photons which energy is much lower than 140.5 keV, this is due to the attenuation of photons in the body of the horse as well as their scattering by the walls of the examination room and by the animal itself. The proportion of radiation attenuated and scattered increases behind a lead screen. The mean energy of the fluence spectrum is around 100 keV in the examination room as well as in the stall. Besides this, behind a lead screen, as the spectrum is modified, the mean energy is 95 keV. RADIOPROTECTION - VOL. 38 ~ No 1 (2003) Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro 67

  8. 1. CLAIRAND rial . . - examinahon r o m - behind a lead screen - - examinahon room -wmout lead protection 1 8 - !\ ', O 1 O0 250 50 300 150 200 Energy (keV) Figure 5 -Gamma specîra collected in the exmination room behind a lead screen, without a lead protection, and ut the stall encrance. Spectre gamma recueilli dans lu salle d'examen derrière un écran de plomb, sans protection plombée, et à l'entrée du box. The spectrometric analysis enabled the overresponse of the FLi to be corrected at low energy and the under-estimation of the electronic dosemeters to be corrected for the photons of energy less than 60 keV. 3.2. Persona1 dosimeîry 3.2.1. Dose to thejïngers skin expresscd in Hp(0.07) Since the calibration of the TLDs leads to the assessrnent of the dose in tenn of kermati,,,, the conversion factors in dose equivalent Hp(0.07)/kermatiss, of 1.43 (ISO, 2000) and Hp(lO)/kerma,issu of 1.68 (KRU, 1992) corresponding to photons of 100 keV, that is the average energy of the fluence spectrum, have been used. The results, given with a global uncertainty of approximately rr 20%, are shown in Table II. The overresponse of FLi in the order of 25 % at low energy was taken into account. The results confirm that, conceming the fingers skin, the most exposed person is the technologist Who prepares the radiopharmaceutical. At the end of the scintigaphic examination, the dose equivalent Hp(0.07) measured on the fjngers RADIOPROTECTION ~ VOL. 38 ~ N" 1 (2003) 68 Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro

  9. EQUiNE SCINTIGRAPHY: ASSESSMENT OF THE DOSE RECEIVED BY THE PERSONNEL TABLE II Skin dose equivalent Hp(0.07) (pSv) meaîurai with FLi. Équivalent de dose à la peau Hp(0,07) (pSv) mesuré à l'aide des FLi. Right ihumb 4 450 Righr index finger 980 Left thumb 320 Left index h g m 750 TABLE III Dose equivaient Hp(l0) (pSv) measured with electronic dosemeters. Équivalent de dose Hp(l0) (pSv) mesuré par les dosimètres électroniques. Under the lead apron ((11 ihr end ofpiiux IJ I I I /('! Over the lead (al the m d u f p h e 1) 1.2 2 8 0.4 Under the lead apron (rit the end of phusr 2 ~ rurnplui5e I + ptuiae 21 Il*! I 2 3 Over the l d (at the end o f a w n phase 2 - suni @se 1 +pfruîe 2) 4 5 17 4 / ( f ) (*' Not recordcd due to technical probleni\ of the technologist ranges from 320 pSv to 980 pSv. The right hand (dominant hand) is on average 1.4 times more exposed than the left one. It should be noted that the preparation time for the radiopharmaceutical here is 15 minutes; given the lack of practice of the technologist on the day of the operation, this will probably be much lower in routine operation. As for the veterinary surgeon, the dose equivalent Hp(0.07) on the fingers skin ranges from 4 to 14 pSv. Taking the maximum value of Hp(0.07) and considering the realistic hypothesis of 150 examinations of this type per year, the annual dose equivalent to the fingers skin of the technologist and the veterinary surgeon is respectively about 150 mSv and 2 mSv. 3.2.2. Dose equivalent Hp(l0) and effective dose Table 1 1 1 shows the dose equivalent Hp( 10) measured using the electronic dosemeters worn on the chest of the operators at the end of phase 1 and at the end of phase 2. These latter correspond to Hp( 10) integrated during the total time of the scintigraphic examination. RADIOPROTECTION ~ VOL. 38 ~ N " Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro 1 (2003) 69

  10. 1. CLATRAND ef al. The results are given with a global uncertainty of 20% for the values around 10 pSv. Below this value, the uncertainty is higher as the minimum detectable dose is about 1 pSv. Besides, the electronic dosemeters under-estimate the dose for low energy photons (< 60 keV); in this case, this under-estimation, about 15% with regards to the meaçured spectrum, has been taken into account. Based on the electronic dosemeters worn on the chest of the operators under the lead apron, the dose equivalent Hp( 10) integrated throughout the examination ranges from 1 to 3 ySv. The highest dose corresponds to that received by the veterinary surgeon Who frequently remains close to the home dunng the examination. Considering 150 examinations per year, the annual effective dose is thus ranging from O. 15 to 0.45 mSv, depending on the operators. It should be noted, however, that the dose rates behind the lead apron being very low, the uncertainty linked to the measurement using this type of dosemeter is high. Based on the electronic dosemeters fitted to the chest of the operators over the lead apron, the dose equivalent Hp( 10) ranges from 4 to 17 ySv. For 150 exam- inations per year, the annual effective dose without the lead apron would therefore range from 0.6 to 2.6 mSv. Phases 1 and 2 lead to very comparable dose equivalents since the longer duration of phase 2 compensates the physical decay of the 99"Tc. 3.3. Ambient dose equivalent rates Table IV shows the ambient dose equivalent rates H*( IO) measured during the various stages of the scintigraphic examination. The ambient dose equivalent rates are given with an uncertainty of k 20%. The ambient dose equivalent rates are very low (< 1 pSv h-') if the radiation is attenuated by lead shield (screen, glass, syringe-shield or transportation box) including in the preparation laboratory. This indicates the benefit of this type of shielding in this application. The ambient dose equivalent rate measured a few meters from the horse or from the fume hood ranges from 1 .5 to 8 pSv hK'. Injection of the radiopharmaceutical leads to ambient dose equivalent rates ranging from 10 to 35 ySv h-' for the stall lad and the veterinary surgeon, respectively. in close proximity to the horse, during the first phase of the examination, the ambient dose equivalent rates may reach levels of about hundreds of pSv h-' 50 cm away from the horse up to 350 pSv h-' in contact with certain anatomical areas like kidneys, which concentrate more than 30% of the radiopharmaceutical 70 RADIOPROTECTION VOL. 38 No 1 (2003) Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro

  11. EQUINE SCINTIGRAPHY: ASSESSMENT OF THE DOSE RECEIVED BY THE PERSONNEL TABLE 1V Ambient dose equivalent rates H*(10) measured during the various stages of the scintigraphic examination. Débits d’équivalent de dose ambiant H*(10) mesurés au cours des différentes étapes de l’examen scintigraphique. Contact with thc fuine hood lcnd gla\s shield syringe (+ syringe-shield) out «f the dose calibrntor Contact with the rume hood lead glass shield. syringc (+ syringe-shicld) out of the dox calihrator I 50 Amhicncc 7 Contact with the transpri box containing the syringe (+ syflngc-shield) In the area ufttœ veterinary surgeon during the injection In €he ilrea of Ihe sratl k d during the injection Control panel for the gamma cilmeril (protected hy a lead screen) O 1 Stage 2 Injection o f the radiqihameu ticu! 35 10 0 4 Bchind lead screcn in ihe exilniinaiion rwm 0 9 50 cm from the flnnk of the horse I 1 1 1 from ihe flenk of thc horse IO7 14 2 m rrom the flank OC ihc horse 25 In contact with the horw: shouldcr‘”) 220 116 357 II6 In convilci with the horsc: hl;idder‘*) In contact wiih ihe horse: kidncysf*’ ln Contact with ihc horse: hindquarters(*’ In contact with the horsc: rear leg‘”’ 43 Ambiencc 8 0.7 Contact wifh the stall. hurse in the centre of the stall Contact wiîh the stall, hom near the stall bars In the middle of the couidor (1 m from the stall) near full Wall, hone against the stall bars In the mtddie of the corridor (1 m from the si&) near thcbars, hwse against the stall bars Bchind lead screcn in the examinaiion room 50 cm frorn the flank or ihe horse 4.5 Stage 5 Waiting phare inside the stnlt 0.7 3 . 5 os 34 1 m froni the flank of thc horse 2 rn from the flank of the horse 17 6 85 In contact with the horse: shoiilder‘:” In Contact with the hase: hladdcr(:’:’ In contac( with the horse: kidneys‘”’ In contnci with the horsc: hindquariers‘*) 85 1 02 5s Amhiencc - 1 5 (*’ See Figure 4. RADIOPROTECTION -VOL. 38 ~ N ” Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro i (2001)

  12. 1. CLAIRAND efrri (Attenburrow et al., 1984). The second phase leads to ambient dose equivalent rates in the vicinity of the horse on average three times lower due to the physical decay of the C)9mTc and the biological elimination of the radiopharmaceutical. 4. Discussion The mean dose to the fingers skin of the technologist Who prepares the radiopharmaceutical is 150 pSv GBq-'. This value is relatively high when compared to the data published in the literature. Some measurements performed using TLDs during the preparation of the 99mTc in human nuclear medicine refer to doses to the fingers skin on average about 70 pSv GBq-' (Williams et al., 1987; Harding et al., 1990; Hastings et al., 1997: Mackenzie, 1997). The dose to the fingers skin here is therefore twice higher than the usual doses in human medicine. This is explained by the lack of practice of the technologist; the preparation time for the radiopharmaceutical will no doubt be greatly reduced in routine operation. There is no specific remark to be made concerning the dose to the fingers of the veterinary surgeon Who injected the radiopharmaceutical as this is very low. about 2 pSv GBq-'. For information, the dose annual limit for the skin is 500 mSv averaged over any 1 cm2 (ICKP, 1991). The dose rates in air measured during this equine scintigraphy are fully comparable to the data published in the literature (Attenburrow and Vennart, 1989: Whitelock, 1997) within the framework of measurements taken under conditions similar to those for this study. Despite the relatively high values of the dose rates in air, the use of appropnate radiological protection during the examination leads to an annual effective dose of less than 1 mSv. Finally, the time scale of 48 hours prior to the horse leaving, which was the subject of a consensus amongst the various teams Who work in this field (Voute et al., 1995; Attenburrow and Vennart, 1989: Whitelock, 1997), seems to be a wholly acceptable compromise from the radiation protection point of view. 5. Conclusion Assuming 150 examinations per year, the annual dose equivalent to the fingers skin of the technologist is at maximum 150 mSv and 2 mSv for the veterinary surgeon: the annual effective dose ranges from 0. 15 to 0.45 mSv, depending on the operators (the maximum dose corresponding to that received by the veterinary surgeon). In the hypothesis where there would have no lead apron, the effective annual dose would range from 0.6 to 2.6 mSv. RADIOPROTECTION - VOL. 38 -No 1 (2003) 72 Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro

  13. EQUINE SCINTIGRAPHY: ASSESSMENT OF THE DOSE RECEIVED BY THE PERSONNE1 This type of installation needs to keep in mind the three main means of protection against external exposure: distance, time and screen. During the operation, the good practices implemented in relation to the radiological risk were noted, both in the use of appropriate protective equipment and in the optimisation of the distribution of roles for each person. Acknowledgments. The authors would like to thank Professor J.M. Denoix's team for its co-operation, which has contributed to the success of this operatioii. REFERENCES Attenburrow D., Bownng C.S., Vennart W. (1984) Radioisotope hone scanning in horses, Equine Ver. J. 16, 121-124. Attenhurrow D., Vennart W. (1989) The application of radioisotope scanning and iinaging in general veterinary practice, Ver. Ann. 29, 15-28. Gambini D.J., Granier R. (1997) Munuelprutique de rudioprorecrion (2e Ed.). E : . Minter, Paris. Harding L.K., Moatafa A.B., Thomson W.H. (1990) Staff radiation doses associated with nuclear me- dicine procedures - a review of some recent measurements, Nucl. Mrd. Commun. 11, 271-277. Hastings D.L., Hillel P.G., Jeans S.P., Waller M.L. (1997) An assessment offinger doses received by staff while prepanng and injecting radiopharmaceuticals, Nud. Med. Commun. 18,785-790. Hoskinson J.J. (2001) Equine nuclear scintigraphy, indications, uses and techniques, Ver. Clin. North Am. Equine Pruct. 17, 63-74. ICRP Publication 60 (1991 ) 1990 Recommendations of the International Commission on Radiological Protection, Ann. fCRP 21( 1-3). ICRU ( 1992) Meusurement of dose equivalenrs ,from external photon und electron radiations, Report 47, ICRU Publication, Bethesda. ISO (2000) Intemational Standard Organisation, NF ISO 4037-3, Rayonnement X et gamma de réfé- rence pour l'étalonnage des dosimètres et des débitmètres et pour la détermination de leur répon- se en fonction de l'énergie des photons. Mackcnk A. (1 997) Reduction of extrernity dose in the radiopharmacy, Nurl. Med. Commun. 18,578- 581. Voute L.C., Wehbon P.M., Whitelock R. (1995) Rules, regulations and safety aspects of scintigraphy, Equine vet. Educ. 7, 169-172. Whitelock R.G. (1997) Radiation hazards froin horses undergoing scintigraphy using technetium-99m, Equinr Vet. J. 29, 26-30. Williams E.D., Laird E.E., Forster E. (1987) Monitoring radiation dose to the hands in nuclear medici- ne: location of dosemeters, Nucl. Med. Commun. 8, 499-503. RADIOPROTECTION - VOL. 38 ~ N " 73 1 (2003) Article published by EDP Sciences and available at http://www.edpsciences.org/radiopro