VNƯ Journal o f Science, Mathematics - Physics 25 (2009) 179-184 Intercomparison on internal dose assessment for Nguyen Van Hung*’*, Bui Van Loat^ ^Nuclear Research Institute, Nguyen Tu Luc, Dalat ^College o f Science, VNU, 334 Nguyen Trai, Thanh Xuan, Ha Noi Received June 2009 A b s t r a c t , r h e p aper resented the results o f a ss e ss in g internal dose for by the direct m e t h o d for V ie t n a m e s e o b j e c t s that w a s iss u e d in the In te rc o m p a riso n P ro g r a m o f I A E A T h e results on e x p e r im e n ta l m e a s u r e m e n t s , c a l c u la t in g intake (I) o f to thyroid b y the s p e c i l i z i n g s y s t e m for m e a su r in g t h > T o i d a c tiv ity , and c o m n iit te d e f f e c t iv e d o s e E ( ) u s in g the s p e c ia liz in g c o d e o f LUDEP w e r e s h o w n that the results carrying out at the N u c le a r R e s e a r c h Institute (I = 1.48.10^ B q, I ’ ( ) n i S v ) w e r e u o o d a n d w e r e in a c c o r d a n c e w ith th e t h o s e o f th e a u t h o r s in o t h e r la b o to rie s in the w orld Keywords: Occupational exposure Intake, Thyroid dose, Committed effective dose, LUDEP 2.0 I Introduction I'herc have been several intcrcomparison exercises organized already at national and international levels for the assessm ent o f occupational exposure due to intakes o f radionuclides to the body These intcrcomparison excrciscs revealed significant differences in approaches, m ethods and assumptions, and C tin^ equently in t h e r e s u lt s ^f'herefore, TAFA o rgiinizeH ÍÌ n e w in t e r c o m p a r is n n exerrii;p in cooperation with the ID EA S projcct under the 5^** EU F ran.^ j r k P ro g ram m e (EU Contract No Ị- IK R -C T 001-00160) and invited participating contrics C ontent o f intcrcomparison cxercises consists o f assessing intakes o f H TO, ^Co, enrichcd uranium, Pu and The results were recci'^ed from 42 countries with 81 participants and 72 reports, in which there were 63 Ị.arlicipants having the reports o f T h e laboratory code o f N o 50 located at the Nuclear Research Institute attended this intercom parison program also [1] I his new intcrcom parison exercisc focuscd especially on the effect o f the guidelines for harmonization o f internal dosimetry It also considered the followw ing aspects: i) to provide possibihiics for the participating laboratories to check the quality o f their internal dose assessment methods in applying the rcccnt ICRP recom m endations (e.g for the new respiratory tract model); ii) to comparc different approaches in interretation o f internal contam ination monitoring data; lii) to quantify the differences in internal dose assesmcnt based on the new guidelines or on other procedures, respectively; iv) lo provide some figures for the influence o f the input parameters on the monitoring results; and v) to provide a broad forum for information exchange [ 1] IAEA organized a new intcrcom parison exercise in cooperation with the ID EA S project under the ELJ Fram ew ork Program m e (EU Contract No F IK R -C T 0 1-00160) and invited participating ' C o n e c s p o n d in g author E -m ail: n g v h u n g @ h c m v n n v n 179 N.v Hung, B.v Loat / VNU Journal o f Science, Mathematics ~ Physics 25 (2009) Ì79-Ỉ84 180 contrics Several cases have been selected for this exercise with the aim o f covering a w ide rangcc o f practices in the nuclcar fuel cyce and in medical applications T he cases were: i) acute intake o f HỈTO; ii) acutc inhalation o f fission products ‘^^Cs and ^®Sr; lii) intake o f ^ C o ; iv) repeated intakes o f ‘l; v) intake o f enrichcd uranium; and vi) single intake o f plutonium radionuclides and [ 1] Based on the equipm ent on measuring activity o f in thyroid and the C om puter Program i for Lung Dose Evaluation in version o f 2.0 (LƯ D EP 2.0) that have had at the N uclear R esearch Instiitute, the case on internal dose assessm ent o f for the radiation w orkers w orking at the radioisoitopc production laboratory by direct method (in-vivo method) was done [2,3]- Experimental 2.7 C ase description In order to evaluate exactly intem al radiation dose, case description had to be e a rn e d out in dectail In case o f evaluating internal dose o f for the radiation w orkers working at the radioiso^topc production laboratories, case description was follows: 2.7./ The event - Description o f the w orking area (Chemical laboratory in a medical institution): The chermical laboratory (belongs to the C enter for Research and Productm o f Radioisotope, N uclear Resecarch Institute) has been used to produce radiopharm aceuticals o f for thyroid diagnosis and therap->y o f patients in nuclear m edicine o f hospitals It consists o f hot cells and production boxes for prepaaring and handling [5] - Characteristics o f w ork (Preparing and handling radiophaưnaceuticals o f for therapccutic purposes): R adiopharm aceuticals o f w ere produced by irradiating T e O j targets during 100 hrs (from M onday m orning to F riday afternoon in a week) at the “neutron a p ” o f Dalat nuclear rcaictor with thermal flux o f 2.2x10^^ n/cm^/sec A fter that, the iư ad iated products w ere handled in the* hoi cells and the boxes in order to b ecom e the radiopharmaceutical o f ’^*1 [2 ] - Reasons for monitoring; initiating event: During handling highly radioactive material (on M onday o f next week), in type o f elementary iodine was released in the air o f the laboratory w'rhich causcs internal exposure to the radiation w orkers through inhalation Therefore on the following dlays, the workers were routinely m onitored via direct m easurem ents (in-vivo') for thyroid as well as via indirect ones (in-vitro) by urine analysis, but the in-vivo m ethod w as used here [2 ,3,4,5] - Actions taken: Because a high level o f activity was m easured in the thyroid, the measurcrment was repeated on the following days 2.1.2 Additional information - Air monitoring: Measurements for radiol'jtive concentration o f in the air o f the laboraitory could be carried out by using the portable sampler for collection o f iodine through activated charrcoal filters After that, radioactive activities on these filters w ere determ ined by the low b ackground garmma spectrometer with H P G e detector From that, radioactive concenưation o f w o u ld be determiined [3] - Chemical form: E lem entary iodine Physical characteristics, particle size: V apour N ose swab, bronchial slime or similar: N one Non removable skin contamination; None - Wound site activity: N.A N.v Hung, B.v Loat / VNU Journal o f Science, Mathematics • Physics 25 (2009) Ỉ 79-184 181 - A ny intervention used (blocking, chclating, etc.): N one L P erso n a l Data Sex: M ale - Age: 50 - W eight: 54 kg 1.4 M o n ito rin g data f o r organ activity A p p ly in g direct technique by the specilizing system for m easuring activity o f in thyroid (the single-channel sp ectrom eter coupled with N al(Tl) detector and the thyroid calibration blocks) [2-5] The m easured th>Toid activity o f with time was showTi in Table Ỉ Intake a n d d ose estimation F ro m the data in Table 1,values o f intake (I) and com m itted effective dose E(50) for were detcm ined with the internal dose assessm ent code o f L U D E P 2.0 T he calculated results were as follows: 1= 1.48.10^ Bq (1) E(50) = 2.32 m S v (2) Table The measured thyroid activity o f f o r the radiation worker Week days (d) Monday of the first week 'ĩuesday Wednesday Thursday Saturday Monday of the second week Wednesday Ihursday SdtuiUay I ’uesday of the third week Thursday Sunday Friday of the fourth week Time after the first day of handling (d) 10 12 15 17 20 25 Thyroid activity o f '^*1 (Bq) 2.05E+03 1.91E+03 1.74E+03 1.44E+03 1.19E+03 9.89E+02 8.20E+02 O.lVLtOi 5.14E+02 4.39E+02 2.43E+02 1.54E+02 Comment One day for handling 1st day of measurement 2nd day of measurement 3rd day of measurement 5lh day of measurement 7ih day of measurement 9th day of measurement 10th day of measurement 12lh day of incasuicincnl 15th day of measurement 17th day o f measurement 20th day of measurement 25th day o f measurement 2.2 D iscu ssion 2.2.1 G eneration o f data set T he data set was generated artificially assum ing an acute intake o f 40 kBq o f on each day o f the three day w o rking period Thus, these intakes during the three consecutive days (a total o f 120 kBq) would give a com m itlcd effective dose o f 2.40 m S v applying the appropriate dose coefficient o f 2.0.10^ Sv/Bq (IC R P -68 and ICRP-78) [1] The predicted thyroid activities w ere generated with internal dose assessm ent code o f IMBA Uncertainties (i.e scatter o f data) w ere then included by assum ing that the m easurem nts follow a lognormal distribution w ith a geom etric standard deviation (i.e SF) o f 1.2 F rom that, the best estimate o f intake per day w as 43.2 kB q (it m eand that the total intake during the three day working period was 130 kBq) Thus, the com m itted effective dose could be calculated as 1.3.10^ X 2.0.10'^ = 2.6.10'^ Sv = m S v [l] 182 N.v ỉỉung, B V Loat / VNU Journal o f Science, Mathematics - Physics 25 (2()()9) Ỉ 79-184 2.2.2 Overall distribiitioii o f resuits The statistical evaluation o f the results, excluding outliers by IA EA and IDEAS was given in T a b le Table Characteristic parameters of the statistical evaluation (excluding outliers) [1] Parameters Intake E(50) 58 50 N 2.57 mSv Geometric mean (GM) 160133 Bq 1.07 Geometric standard deviation (GSD) 1.39 Arithmetic mean (AM) 169659 Bq 2.58 mSv 0.17 niSv Arithmetic standard deviation (ASD) 62153 Bq Minimum 88000 Bq 2.2 mSv Maximum 329000 Bq 3.0 niSv 3.74 Max/Min ratio 1.36 Outliers 13 The below figures show n frequency distributions and ratios o f all individual results n o rm alized to the geometric mean Fig Frequency distribution o f results without outliers (N = 58) '^*1 normalized to the geometric mean ( GM= 160n Rq G S D = 1.36) n i ũ Fig Ratios o f all individual results normalized to the geometric mean (GM = 160133 Bq, GSD = 1.36, N = 58) The outliers were indicated with blank colunms [1] N V HuníỊ B y Loat / VNLỈ Journal o f Science Mathematics - Physics 25 (2009) ! 79-184 183 E (5 )/G M ỈMg F r e q u e n c y d istrib u tion o f r e su lts w it h o u t o u tlie r s ( N “ ) V a lu e s o f c o m m it t e d e f f e c t iv e d o s e d ue to n o r m a liz e d to the g e o m e t r i c m e a n ( G M = m S v , G S D = ) [1] 10 - 66 Ifl I'''"**"*" 0.1 ID Ig Ratios o f all in d iv id u a l resu lts n o r m a l i z e d to the g e o m e t r i c m e a n ( G M = m S v , G S D = 1.07, N = 50) T h e o u t li e r s w e r e in d ic a t e d w it h b la n k c o l u m n s [1] Laboratory cod e o f V ietnam w a s 50 T h u s the calculated values o f intake and E(50) from the code o f 50 were good and not belon ged outliers 2.2.Ỉ Identification o f outliers Outliers w ere identified by the statistical c n te ria described in the Table Total num ber o f submitted results from the participants w ere 63 for intake and 63 for E(50), and num ber o f identified outliers were for intake and 13 for E(50) 184 N V Hung B V Loat / VNU Journal o f Science, Mathematics - Physics 25 (2009) 179-184 2.2.4 Softw are used A ltogether 20 different internal dosim etry software were used by the participants The most frequently used software code w as IM BA, but other program m es were also used by m ore participants Twelve participants used IM BA, six used LU D EP, four used M O N D A L , w hereas three participants used IMIE o r AIDE, two indicated the use o f IDEAS D V 0102 and M athem atica - Excel, w hile one participant used other 13 codes As m any as 17 participants declared that they used no softw are but manual evaluation methods In the used softw are o f LU D E P , intake retention fractions and dose coefficients w ere based “ Human Respiratory I'ract M o d el”, “Gastrointestinal Tract M o del” , and “Systemic Biokinetic M o d e l” in ICRP-66, ICRP-30, and ICRP-54, respectively [2-5], Conclusion The laboratory on internal radiation dosimetry o f N uclear R esearch Instate had attended the intercom panson on internal dose assessm ent for intake o f through inhalation by the direct method (in-vivo method) The m easured and calculated results o f intake (I = 1.48.10^ Bq) and com m itted effective dose (E (50) = 2.32 m Sv) for w ere shown that they w ere good (w ith error o f 10% in com parison with the reference values) and were in accordance with the results o f other authors attending the research cooperation project Thus, they were also issued in the specialized book nam ely as IA E A -T E C D O C -1568 (Intercom parison Exercise on Internal Dose A ssessm ent, Final report o f a joint lA E A -ID E A S project, IAEA, Sept 2007) [1], This w ork IS financially supported by Joint lAEAIDEAS Project, IA E A -T E C D O C -1568 and QG 09-06 Project References [ij lA b A , in te rc o ỉn p a n so ti exercise on inlcnal d o se a ssessm eni, h in a l re p o rt o l a jo i n i lA b A - lD b A S p ro jc c i, lA h A - TECDOC-1568, September 2007 [2] Nguyen Van Hung, R esearch in in tern a l se íỉosim eírỵ b a sed on m eth o d s o f w h o lc-h o d y m ea su rem en t a n d Ịỉum an urine analysis, PhD thesis in physics (in Vietnamese), MOET, September 2003 [3] Hoang Van Nguyen, Nguyen Van Hung cl al Som e resea rch es ỉn the fi e l d o f d ia tio n dosim etry' Final report o f ihc ministry’s research project for 1998-1999 (in Vietnamese), MOST, March 2000 [4] Nguyen Van Hung et al., in te rn a l radiation d o sim etry f o r so m e o f g a m tn a em ittin g d io n u clid es by a chair-type w hole-body cou n ter u sin g a scin tillation detector Final report o f the institute’s research projcct for 2003 (in Vietnamese), VAEC, August 2005 [5] Nguyen Van Hung ct al., R esearch in internal dosim etry' f o r radiation w o rkers f o r so m e o f g a m m a em itting radionuclides hy d irect m eth o d w ith using a ch a ir-typ e w iiole-hody countcr Final report o f the institute’s research project for 2002 (in Vietnamese), VAEC, March 2003 ... [2-5], Conclusion The laboratory on internal radiation dosimetry o f N uclear R esearch Instate had attended the intercom panson on internal dose assessm ent for intake o f through inhalation by... the thyroid, the measurcrment was repeated on the following days 2.1.2 Additional information - Air monitoring: Measurements for radiol'jtive concentration o f in the air o f the laboraitory... was done [2,3]- Experimental 2.7 C ase description In order to evaluate exactly intem al radiation dose, case description had to be e a rn e d out in dectail In case o f evaluating internal dose