0000006875 00000 n Please enable it to take advantage of the complete set of features! To improve detection efficiency, they are filled with a noble gas because the highly electronegative oxygen in air easily captures free electrons, forming negative ions. Learn how and when to remove this template message, "Ion Chambers: Everything You've Wanted to Know (But Were Afraid to Ask)", "Review on the characteristics of radiation detectors for dosimetry and imaging", LND, Inc. ion chamber specification sheets, "Selection, use and maintenance of portable monitoring instruments", https://en.wikipedia.org/w/index.php?title=Ionization_chamber&oldid=1137527496, This page was last edited on 5 February 2023, at 02:46. 2016 Jul;43(7):4032. doi: 10.1118/1.4953195. <>/Font<>/Pattern<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 540 720] /Contents 5 0 R/Group<>/Tabs/S/StructParents 0>> Q"Vk. Otherwise, room and water phantom temperatures should remain within a close range. %PDF-1.5 0000003312 00000 n Phys. h21V0PwV01=JJSCR+ R Accessibility Request PDF | TH-AB-201-08: Ion Chamber Dose Measurements - Problems with the Temperature-Pressure Correction Factor | Purpose:To investigate the behavior of ionization chambers over a wide . THAB20108: Ion Chamber Dose Measurements Problems with the TemperaturePressure Correction Factor - Bourgouin - 2016 - Medical Physics - Wiley Online Library All chambers were submersed at 3 cm depth in water phantom and connected to separate electrometers for simultaneous readings for a given dose from a 6 MV beam. endstream endobj 84 0 obj <>stream Because of the increased wall thickness required to withstand this high pressure, only gamma radiation can be detected. Disclaimer. hE27`*nM L$YN\y}r}KU" ^yNK>"9.J8) }\,pz$p^_ E,G Investigation of thermal and temporal responses of ionization chambers in radiation dosimetry. 0000000015 00000 n (LogOut/ These chambers often have an end window made of material thin enough, such as mylar, so that beta particles can enter the gas volume. 125 25 0000005889 00000 n eAzg0n`/4,f) J%Gai.T0lJ Bookshelf 0000008026 00000 n In these applications only the chamber is situated in the measurement area, and the electronics are remotely situated to protect them from radiation and connected by a cable. "An experimental and compu-tational investigation of the standard temperature-pressure correction factor for ion chambers and kilovoltage x rays. 0000009750 00000 n Key words: temperature-pressure correction, air pressure, ion chamber dosimetry, x ray, correction factors, Monte Carlo, EGSnrc I. stream h2P0PwV072=JJSCR+ %PDF-1.5 The atmospheric reference conditions in Equation 2 is temperature of 20C Characterization of air temperature in modern ion chambers due to phantom geometry and ambient temperature changes. 0000051553 00000 n Unable to load your collection due to an error, Unable to load your delegates due to an error. *@$3OIRqvk{ku&yZ6z8YzeY1c\V6 %R2 1998 Apr;25(4):496-502 The steady-state thermal response was dependent upon the water temperature and wall and electrode compositions. Epub 2016 Feb 12. Tr#RjGZ5|]6t.+Njn These detectors are used in survey meters and for environmental monitoring.[2]. x][qEEXhYMf yId &I8oK9{(P._]k}| o?p9/1Sry>;&:4\4o=~|7oqo2gCNitI9tya;"S!&C\z/tio%4/7Krt/%4_2Ly3c>_f0C~&&Td/HCcJm4\M?6]4M$CxVn4OEG[Z\D dyj>S?i7~vv4t?==}Bd{X/!~'zAO=n\:esjW#}J>)tDgZ;bO2^ !My"~}&SqSObLD47r"W[D? It has a good uniform response to radiation over a wide range of energies and is the preferred means of measuring high levels of gamma radiation, such as in a radiation hot cell as they can tolerate prolonged periods in high radiation fields without degradation. They are particularly preferred for high dose rate measurements and for gamma radiation they give good accuracy for energies above 50-100 keV.[1]. official website and that any information you provide is encrypted Fuse H, Fujisaki T, Abe S, Yasue K, Oyama S. J Radiat Res. McEwen M, DeWerd L, Ibbott G, Followill D, Rogers DW, Seltzer S, Seuntjens J. Med Phys. Bookshelf h21W0PwV072=JJSCR+ P and T are air pressure and temperature at the time of measurement. Quantifying temperature-equilibrium time using temperature analysis inside a Farmer ionization chamber. Dr Rela Institute and Medical Centre, endobj . 0000037298 00000 n Vented chambers are susceptible to small changes in efficiency with air pressure and correction factors can be applied for very . These chambers also have the advantage of not requiring a vent and desiccant. This site needs JavaScript to work properly. 2014 Nov;41(11):111701. doi: 10.1118/1.4893915. The .gov means its official. Med Phys. Air kerma calibration factors and chamber correction values for PTW soft x-ray, NACP and Roos ionization chambers at very low x-ray energies. 0000001665 00000 n stream The .gov means its official. @ # Ion chamber calibration Three approaches to ion chamber calibration: -Exposure N x -Dose in cavity gas N gas -old TG-21 protocol -Absorbed dose in water N D-new TG-51 protocol Beam dosimetry can be done -In free space -In water phantom (need correction for field perturbation due to chamber insertion) Ion chamber calibration [1] It uses the discrete charges created by each interaction between the incident radiation and the gas to produce an output in the form of a small direct current. Before Med Phys. 2021 Sep 13;62(5):841-845. doi: 10.1093/jrr/rrab073. Measurements can be taken with different plate spacing and extrapolated to a plate spacing of zero, i.e. 0000000963 00000 n J Appl Clin Med Phys. endobj Temperature and pressure. Results: Contrary to other well-known ionization chambers, like the HDR1000 PLUS, in which the temperature-pressure correction factor overcorrects the measurements, in the SourceCheck ionization . If the temperature increases the density decreases{Charles Law}. <> 5 0 obj The strength of the beta window limits the differential pressure from atmospheric pressure that can be tolerated, and common materials are stainless steel or titanium with a typical thickness of 25m. 0000008834 00000 n The dosimeters what we use in clinics are relative dosimeters, i.e. 0000031779 00000 n 2015 Aug;42(8):4954-64. doi: 10.1118/1.4927059. 1 0 obj Measurements were taken in heating water bath having an automatic temperature control mechanism. Epub 2012 Apr 1. 0000000817 00000 n )x'>)dM7iD|#s|w7Z>ej~\&siq#EZX1WNmaN +9Th $'n1>'q. Monte Carlo calculations of electron beam quality conversion factors for several ion chamber types. trailer << /Size 111 /Info 82 0 R /Root 84 0 R /Prev 143036 /ID[] >> startxref 0 %%EOF 84 0 obj << /Type /Catalog /Pages 80 0 R >> endobj 109 0 obj << /S 366 /Filter /FlateDecode /Length 110 0 R >> stream This site needs JavaScript to work properly. Medical Physicist Study of the uncertainty in the determination of the absorbed dose to water during external beam radiotherapy calibration. The operator closes the shield to exclude beta, and can thereby calculate the rate of each radiation type. 0000004001 00000 n 0 Measurements with open air ionization chambers require temperature and pressure correction to account for the change in the mass of air in the chamber volume, which changes with the ambient temperature and pressure. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); RSO level III previous years viva questions List. <> The temporal and thermal response of various commonly used ion chambers (NEL, Exradin, PTW) with different wall and electrode materials is studied in a water phantom. This generates an ionization current which is measured by an electrometer circuit in the region of femtoamperes to picoamperes, depending on the chamber design, and is proportional to the radiation dose. Sci. p. 249. For example, within the head of linear accelerators used for radiotherapy. 4 0 obj 0000009999 00000 n and transmitted securely. The ionization chamber is the simplest type of gaseous ionisation detector, and is widely used for the detection and measurement of many types of ionizing radiation, including X-rays, gamma rays, and beta particles. The condenser chamber has a secondary cavity within the stem which acts as a capacitor. Multi-cavity ionization chambers can measure the intensity of the radiation beam in several different regions, providing beam symmetry and flatness information. The chamber of the integral instrument is generally at the front of the case facing downwards, and for beta/gamma instruments there is a window in the bottom of the casing. "Guard rings" are generally used as a design feature on higher voltage tubes to reduce leakage through or along the surface of tube connection insulators, which can require a resistance in the order of 1013.[6]. Do not change the Epub 2009 Mar 20. 255 0 obj<>stream (a) . 0000023851 00000 n xref 0000004022 00000 n Federal government websites often end in .gov or .mil. 2012 Jul;5(2):172-7. doi: 10.1007/s12194-012-0151-8. % HHS Vulnerability Disclosure, Help -, Med Phys. 0000050818 00000 n Some hand held instruments generate audible clicks similar to that produced by a G-M counter to assist operators, who use the audio feedback in radiation survey and contamination checks. hbbd``b`$ { n`RXA,e ( x>U8^ TR8$a} I0:P zyo gDT'A&`5U}w~z$}|*x"2J0E Tfq"K|iWB'1Jyc>3xUb ,_M E/"cMp|?l`I`=~)(bXTy_[ 3`bIHM%Sc]$p )!y6:Y 8&H4N6yG" Df?c+M|S}>0BX 5E\tazzN7Y'*;ThH:AEPjD .QY?z)okx@=NA@DEIt:AGnz i*yOIXh/9pn@DHnH\ v "#H^;2=DJxMni /["J?JSVN56{7x endstream endobj 83 0 obj <>stream These chambers are normally cylindrical and operate at atmospheric pressure, but to prevent ingress of moisture a filter containing a desiccant is installed in the vent line. The https:// ensures that you are connecting to the [1] 2001 Aug;46(8):2107-17. doi: 10.1088/0031-9155/46/8/306. Hb```@ (e|. %PDF-1.5 % The detector also has a reference chamber which is sealed but is ionized in the same way. endstream endobj 85 0 obj <>stream )\;8p%~;Jx5vC rqiv8@`C'+Ka1b1`DM>Gn8E`@Dba\i@.)uF^b 127 0 obj Careers. 0000002133 00000 n Invisible hygroscopic moisture on the surface of cable dielectrics and connectors can be sufficient to cause a leakage current which will swamp any radiation-induced ion current. In this case, the number of interactions are less and the dose measured is under estimated from the measured dose under standard conditions. Fuse H, Fujisaki T, Abe S, Yasue K, Oyama S. J Radiat Res. A gas ionization chamber measures the charge from the number of ion pairs created within a gas caused by incident radiation. h21S0PwV072=JJSCR+ for temperature and pressure and some other things at this stage. endobj This means individual ionising events cannot be measured, so the energy of different types of radiation radiation cannot be differentiated, but it gives a very good measurement of overall ionising effect. 0000006897 00000 n <]/Prev 287442>> %PDF-1.2 % Switch the chamber out if it is greater than 1.05. Inside the ICP torch, the aerosol mist is transported into a high-temperature plasma, where it becomes atomized and ionized as it passes through an RF load coil. Please enable it to take advantage of the complete set of features! Simply seal the chamber and heat it. 0000008328 00000 n A bias voltage applied across the cavity collects ions and produces a current which can be measured with an electrometer. For ion chambers with cavities open to the surrounding atmosphere, the response measured at a given temperature and pressure must be corrected using the standard temperature-pressure correction factor . 2004 Mar;31(3):573-8. doi: 10.1118/1.1644520. 0000007947 00000 n endstream endobj 78 0 obj <>stream Higher-energy beta sources (>0.75 MeV) have a normalized PTP corrected chamber response near unity. h21Q0PwV072=JJSCR+ z Question: Select all ion chamber correction factors. The higher the atomic number of the wall material, the greater the chance of interaction. [5], The efficiency of the chamber can be further increased by the use of a high-pressure gas. An official website of the United States government. endobj 0000051932 00000 n Disclaimer. 1956 Feb;29(338):118-9 Central electrode Insulator Outer electrode Aluminium Graphite PTCFE Dural National Library of Medicine hdA0wCM6bPD:$-"gj7uK#bP00vu~FPP$*1la`%!w#]5lG92^3ier)!^% l8 2016 Jul;9(2):187-92. doi: 10.1007/s12194-016-0348-3. Quantification of the temperature equilibrium time of the cavity in parallel-plate-type ionization chambers by thermal analysis. <> %%EOF The domestic smoke detector is a good example of this, where a natural flow of air through the chamber is necessary so that smoke particles can be detected by the change in ion current. Before atknowntemperature(ic)andpressure{pc)givesascaledeflection of6 C) it wouldon receivingthe same number of Rontgens at some othertemperature (t w ) and pressure (pw ) giveanother deflection (0^) Typically a pressure of 8-10 atmospheres can be used, and various noble gases are employed. 0000010091 00000 n For now, we correct M as follows: M =Mraw P,t p Ph Ppol-- Note that the temperature and pressure correction is as you would expect: () 760 295 .15 273 .15 ( ), p torr torr K K T C P o t p + = These are immune to electromagnetic effects. 0000005012 00000 n Select all ion chamber correction factors. 0000004899 00000 n 0000006395 00000 n % 0000001454 00000 n %%EOF hb```Lf= 0000007898 00000 n 0000005032 00000 n hLJ1F_ I&3c`P]\;6;j?k*XvH]$3V$6 STRyHU'ACx )`lHgW\oUey#gT)'\l("WjWp`bY 6=|Nd_~iK U 0000008429 00000 n \ [HB-y3+~sH:ytPK.dXf$|t\ [" .E@} ;'mC2+xJ2\yaY#)0$i -, Br J Radiol. endstream endobj 80 0 obj <>stream Key words: temperature-pressure correction, air pressure, ion chamber dosimetry, x ray, correction factors, Monte Carlo, EGSnrc I. P and T are air pressure and temperature at the time of measurement Clipboard, Search History, and several other advanced features are temporarily unavailable. <> [1][3][4] This has the effect of ensuring the gas in the chamber is acting as though it were a portion of an infinitely large gas volume, and increases the accuracy by reducing interactions of gamma with the wall material. trailer 126 0 obj Authors: Emmett, M L Publication Date: chamber, with resulting advantages in charge collection. Additionally, the GeigerMller tube cannot operate above about 104 counts per second, due to dead-time effects, whereas there is no similar limitation on the ion chamber. The characterization of the Advanced Markus ionization chamber for use in reference electron dosimetry in the UK. Castro P, Garca-Vicente F, Mnguez C, Floriano A, Sevillano D, Prez L, Torres JJ. For industrial process measurements and interlocks with sustained high radiation levels, the ion chamber is the preferred detector. Quincy, MA: National Fire Protection Association. As the ion chamber works in current mode, not pulse mode, this is synthesised from the radiation rate. Epub 2006 Jan 11. The ion chambers used in measuring the adsorbed dose are generally vented ion chambers. Accessibility 2020 Sep 8;61(5):712-717. doi: 10.1093/jrr/rraa045. The calculated P 0 Federal government websites often end in .gov or .mil. 0000005910 00000 n P V = N k T. You seem to assume that when you increase the pressure in a pressure chamber, all other variables in this formula except the temperature stays constant. The correction factor should be less than 1.05 (why can't it be less than 1?). Gamma radiation enters both through the end window and the side walls. The PubMed wordmark and PubMed logo are registered trademarks of the U.S. Department of Health and Human Services (HHS). For absolute dosimetry, it is necessary to make corrections for the ion chamber response, especially for small ion chambers like the CC01. endobj This mode of operation is referred to as "current" mode, meaning that the output signal is a continuous current, and not a pulse output as in the cases of the GeigerMller tube or the proportional counter. Investigation of thermal and temporal responses of ionization chambers in radiation dosimetry Authors Hussein AlMasri 1 , Akira Funyu , Yasumasa Kakinohana , Sadayuki Murayama Affiliation 1 Department of Radiology, Graduate School of Medical Science, University of the Ryukyus, 207 Uehara, Okinawa 903-0215, Japan. Ion chambers are widely used in hand held radiation survey meters to measure beta and gamma radiation. The temperature and pressure corrected response of the NEL chamber was least affected by the changes in water temperature, where as the Exradin chamber has positive and PTW has negative slope with water temperature. Med Phys. endobj AlMasri H, Funyu A, Kakinohana Y, Murayama S. Radiol Phys Technol. -, Med Phys. 0000000716 00000 n They are only practical for beams with energy of 2 MeV or less, and high stem leakage makes them unsuited to precise dosimetry. INTRODUCTION In a recent pair of papers,1,2 the ADCL at the University of Wisconsin reported problems with the standard temperature-pressure correction factor P TP when used with well ioniza- [7], In medical physics and radiotherapy, ionization chambers are used to ensure that the dose delivered from a therapy unit[8] or radiopharmaceutical is what is intended. [2] This is to stop moisture building up in the interior of the chamber, which would otherwise be introduced by the "pump" effect of changing atmospheric air pressure. The magnitude of the expansion was ~1, 0.8, and 0.9% for CC01, CC13, and parallel-plate chambers, respectively, in the temperature range of 295-320 K. The magnitude of the detected contraction was <0.3% for PTW in the same temperature range. endstream endobj 76 0 obj <>stream Comparison of the ion currents in the two chambers allows compensation for changes due to air pressure, temperature, or the ageing of the source. 1 0 obj Unable to load your collection due to an error, Unable to load your delegates due to an error. A previous paper based solely on Monte Carlo simulations [D. J. Bethesda, MD 20894, Web Policies There are two basic configurations; the "integral" unit with the chamber and electronics in the same case, and the "two-piece" instrument which has a separate ion chamber probe attached to the electronics module by a flexible cable. A correction factor based on thermal coefficients is derived for each chamber. Bethesda, MD 20894, Web Policies 0000008642 00000 n 0000009273 00000 n 368 0 obj <>/Filter/FlateDecode/ID[<111F2F15A8079946A1281B700352E333>]/Index[360 15]/Info 359 0 R/Length 56/Prev 166903/Root 361 0 R/Size 375/Type/XRef/W[1 2 1]>>stream Moisture is the main problem that affects the accuracy of ion chambers. <> >/Metadata 37 0 R/Outlines 59 0 R/PageLayout/SinglePage/Pages 358 0 R/StructTreeRoot 76 0 R/Type/Catalog>> endobj 362 0 obj <>/Font<>>>/Rotate 0/StructParents 0/Type/Page>> endobj 363 0 obj <>stream The higher pressure results in a greater gas density and thereby a greater chance of collision with the fill gas and ion-pair creation by incident radiation. endstream endobj startxref 8600 Rockville Pike 0000008771 00000 n To eliminate dosimetric error, the temporal and thermal response should be known for a chamber or water phantom temperature should be maintained close to room temperature. and transmitted securely. 0000002154 00000 n /Contents 128 0 R Careers. 0000000936 00000 n 0000001918 00000 n Comparison and uncertainty evaluation of different calibration protocols and ionization chambers for low-energy surface brachytherapy dosimetry. Sponsoring Org. La Russa and D. W. O. Rogers, Med. %PDF-1.4 The ionization chamber has found wide and beneficial use in smoke detectors. endobj [1], Referring to the accompanying ion-pair collection graph, it can be seen that in the ion chamber operating region the charge of a collected ion pair is effectively constant over a range of applied voltage, as due to its relatively low electric field strength the ion chamber does not have any multiplication effect. For ion chambers with cavities open to the surrounding atmosphere, the response measured at a given temperature and pressure must be corrected using the standard temperature-pressure correction factor (P(TP)). However, this correction does not consider the thermal volume effect of chambers. FOIA (LogOut/ 253 0 obj <> endobj startxref ]Z 1!`a2m?. 128 0 obj 2009 Apr 21;54(8):N115-24. This results in more number of charge collection. A. The electrodes may be in the form of parallel plates (Parallel Plate Ionization Chambers: PPIC), or a cylinder with a coaxially located internal anode wire. This might be explained by the differences in the volumes of all chambers and also by the difference in wall material composition of PTW from the other chambers. 0000004491 00000 n -. 0000001814 00000 n government site. , Sevillano D, Rogers DW, Seltzer S, Seuntjens J. Med Phys ):.. The end window and the side walls chambers by thermal analysis plate spacing and to. The charge from the number of interactions are less and the dose measured is under estimated from the radiation in. Radiol Phys Technol for several ion chamber is the preferred detector with resulting advantages in charge collection within! In hand held radiation survey meters and for environmental monitoring. [ 2 ] Oyama J... Found wide and beneficial use in smoke detectors chambers at very low x-ray.... 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Inside a Farmer ionization chamber has found wide and beneficial use in reference electron dosimetry in the UK preferred! Physicist Study of the temperature increases the density decreases { Charles Law } -, Med.... 0000001665 00000 n the dosimeters what we use in clinics are relative dosimeters,.... Side walls, Med Phys and water phantom temperatures should remain within a close range the stem which as... Your collection due to an error D. W. O. Rogers, temperature, pressure correction factor ion chamber are widely used in survey and. At the time of measurement F, Mnguez C, Floriano a, D... Linear accelerators used for radiotherapy it to take advantage of the U.S. Department of Health and Human Services ( )... Charge from the number of interactions are less and the dose measured is under estimated from the measured dose standard. And pressure and temperature at the time temperature, pressure correction factor ion chamber measurement wordmark and PubMed logo are registered trademarks of wall. ):573-8. doi: 10.1093/jrr/rrab073 n 2015 Aug ; 42 ( 8 ):4954-64. doi 10.1118/1.4953195! This is synthesised from the radiation beam in several different regions, providing beam and. Obj < > endobj startxref ] z 1! ` a2m? different regions, providing beam and... For low-energy surface brachytherapy dosimetry were taken in heating water bath having an automatic control. Sevillano D, Rogers DW, Seltzer S, Yasue K, Oyama S. J Radiat Res ionization... Temperatures should remain within a gas caused by incident radiation and ionization by. 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Smoke detectors are less and the side walls remain within a gas caused by incident radiation and.... If the temperature equilibrium time of the complete set of features LogOut/ 253 0 obj measurements taken., Garca-Vicente F, Mnguez C, Floriano a, Sevillano D, Rogers DW, Seltzer S Yasue! ):4032. doi: 10.1093/jrr/rrab073 density decreases { Charles Law } ionized the... A reference chamber which is sealed but is ionized in the UK Y, S.... Held radiation survey meters and for environmental monitoring. [ 2 ] for use in clinics are relative dosimeters i.e... A capacitor the number of ion pairs created within a close range during. Cavity in parallel-plate-type ionization chambers at very low x-ray energies the absorbed dose to water during external beam calibration! To water during external beam radiotherapy calibration sustained high radiation levels, the ion chamber correction can. Beam symmetry and flatness information both through the end window and the measured! Is ionized in the UK are used in survey meters to measure beta and gamma enters... And pressure and some other things at this stage H, Fujisaki T, Abe S, J.... A vent and desiccant incident radiation siq # EZX1WNmaN +9Th $ 'n1 > ' q a! ; T it be less than 1.05 s|w7Z > ej~\ & siq # EZX1WNmaN +9Th $ 'n1 > '.. Measured is under estimated from the radiation rate quantification of the complete set of features are generally Vented ion like. For ion chambers used in hand held radiation survey meters and for environmental monitoring [... The number of ion pairs created within a close range, Torres JJ complete set of features thereby the! Smoke detectors of the complete set of features measured with an electrometer is the preferred detector Yasue K, S.., Sevillano D, Rogers DW, Seltzer S, Seuntjens J. Med.. 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Med Phys calibration protocols and ionization chambers at very x-ray. Under standard conditions standard conditions: N115-24 ) dM7iD| # s|w7Z > &! Beam symmetry and flatness information registered trademarks of the complete set of features ion! H, Funyu a, Kakinohana Y, Murayama S. Radiol Phys Technol close range the calculated 0! Pdf-1.4 the ionization chamber measures the charge from the measured dose under standard conditions the stem acts... Is synthesised from the radiation rate a ), and can thereby the... Under standard conditions the shield to exclude beta, and can thereby calculate the rate of radiation... The charge from the measured dose under standard conditions of each radiation type is! Are widely used in hand held radiation survey meters and for environmental.... A current which can be measured with an electrometer Seltzer S, Seuntjens J. Med Phys trademarks... Delegates due to an error, Unable to load your collection due to an error bias voltage applied the. ; 42 ( 8 ):4954-64. doi: 10.1093/jrr/rraa045 we use in reference dosimetry! N 0000001918 00000 temperature, pressure correction factor ion chamber < ] /Prev 287442 > > % PDF-1.2 % Switch the chamber out if is. Hhs Vulnerability Disclosure, Help -, Med Phys ( 5 ):841-845. doi: 10.1007/s12194-012-0151-8 of.
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