EP0071826A2 - Chambre dosimètre pour électron et rayonnement X - Google Patents

Chambre dosimètre pour électron et rayonnement X Download PDF

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Publication number
EP0071826A2
EP0071826A2 EP82106592A EP82106592A EP0071826A2 EP 0071826 A2 EP0071826 A2 EP 0071826A2 EP 82106592 A EP82106592 A EP 82106592A EP 82106592 A EP82106592 A EP 82106592A EP 0071826 A2 EP0071826 A2 EP 0071826A2
Authority
EP
European Patent Office
Prior art keywords
electrode
signal
ring
dose monitor
measuring
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP82106592A
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German (de)
English (en)
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EP0071826A3 (en
EP0071826B1 (fr
Inventor
Leonhard Taumann
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Siemens AG
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Siemens AG
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Publication date
Application filed by Siemens AG filed Critical Siemens AG
Publication of EP0071826A2 publication Critical patent/EP0071826A2/fr
Publication of EP0071826A3 publication Critical patent/EP0071826A3/de
Application granted granted Critical
Publication of EP0071826B1 publication Critical patent/EP0071826B1/fr
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J47/00—Tubes for determining the presence, intensity, density or energy of radiation or particles
    • H01J47/02—Ionisation chambers

Definitions

  • the present invention relates to a dose monitor chamber for radiation.
  • this invention relates to a dose monitor chamber for electrons or X-rays, preferably for use in or in conjunction with a linear accelerator.
  • U.S. Patent No. 4,131,799 discloses a dose monitor chamber or ionization chamber which is employed to monitor the radiation exiting from a particle accelerator. Of interest is not only the totally emitted radiation intensity but also the (uniform or irregular) distribution of the radiation within the emitted radiation cone.
  • the known monitor chamber detects all kinds of nonhomo g eneities of the dose rate. In particular, it is applicable for determining asymmetries as well as changes of electron or X-ray distribution.
  • the ionization chamber according to the prior art comprises essentially a first electrode arrangement in a first plane and a second electrode arrangement located in a second plane parallel to the first plane.
  • the first arrangement contains a round central plate which functions as an electrode and which is surrounded by four further plates.
  • the ionization chamber further comprises a spacing ring for keeping the second arrangement of electrodes in a plane parallel to the first arrangement, thereby forming a first chamber.
  • the second electrode arrangement is a round plate which is supplied by a high voltage. The current derived from the individual measuring electrodes is proportional to the dose rate received in the corresponding measuring volume. To the ionization chamber is connected a second chamber, where the totally received dose rate is measured.
  • a dose monitor chamber comprises a first and a second measuring electrode.
  • the first measuring electrode is essentially a first ring portion which at its circumference extends from 0° to approximately 180°, in particular a little less than 180° or a little more than 180°.
  • the second measuring electrode is located in the same plane as the first measuring electrode. It comprises a full inner circular area to the periphery of which a second ring portion adjoins in an electrically conducting manner.
  • the first ring portion and the second ring portion are electrically s.eparated from one another at their facing ends.
  • the inner rim of the first ring portion is electrically separated form the rim of the inner circular area.
  • the measuring electrodes are electrically insulated from each other by a given distance. The construction is such that the first and the second ring portion combined are approximately 360°.
  • the measuring electrodes are preferably thin electrically conductive layers affixed.to an insulating material.
  • both electrode signals are weighted and then compared with each other in a comparator. If radiation symmetry prevails, the weighted electrode signals will be equal.
  • each of the areas of the first and of the second ring portion is half the area of the inner circular area. Consequently, in case of symmetry and homogeneity, one electrode signal is smaller than the other by a factor-of 3. This imbalance can be adjusted by weighting during the processing of the signals.
  • the first ring portion of the first measuring electrode may extend from 0° to approximately 160°, i.e. a little less than 180°, or it may extend from 0° to approximately 200°, i.e. a little more than 180°.
  • asymmetries can be detected in a radial axis which passes along the facing edges of both ring portions. In designs actually implemented values of 157.5° and 202.5°, respectively, have been applied.
  • the distance between the first and the second measuring electrodes is chosen in accordance with the applied voltage and with the insulating ability of the applied insulating material.
  • the distribution of the radiation intensity or dose rate I is platted in a direction r across to the central beam of a linear accelerator.
  • the radiation can be electron or X-ray radiation.
  • the locations +R and -R indicate the points of the strongest rise of intensity I and concurrently roughly the radius of the ionization chamber illustrated in Fig. 2.
  • a regular or even distribution of intensity I is attained, which is represented by the curve g in Fig. 1.
  • the curve a shows, for instance, an asymmetrical distribution.
  • the intensities in the outer areas" -that is close to the locations +R, -R are of differing size.
  • the measuring space 4 of an ionization chamber 2 is essentially formed by a first electrode plate 6, a spacing ring 8 and a second electrode plate 10.
  • the first electrode plate 6 contains a first circular insulating plate 12 which is provided on its upper side with an electrically conductive layer 14 that is electrically grounded.
  • the first insulating plate 12 can be either a ceramic plate or a plastic foil. A ceramic plate is preferably applicable for X-ray radiation monitoring,and a synthetic foil is preferred for monitoring or measuring electrons.
  • the lower side of the first insulating plate 12 is provided on its outer rim with an auxiliary electrode which acts as a protective ring 16 and which is also grounded.
  • this first insulating plate 12 In the middle region of the lower side of this first insulating plate 12 there is located a two-electrode arrangement. As shown in detail in Fig. 3, two flat measuring electrodes 18 and 20 are applied here to the insulator plate 12, for instance, by evaporation. They are both located in the same plane.
  • the two-electrode arrangement 18,20 has a characteristic design.
  • the first measuring electrode 18 is essentially a first ring portion which extends from one face end to the other from 0° to 202.5°.
  • the second measuring electrode 20 consists of a somewhat more complex structure. One can visualize that this second measuring electrode 20 encompasses a full inner circular area 22 (indicated by broken lines), which is surrounded by a . second ring portion 24. Both ring portions 18 and 24 have the same inner and outer radius. At both its ends the second ring portion 24 is electrically separated from the ends of the first ring portion 18 by a nonconductive gap or separating groove 26 and 28, respectively.
  • All the separations or grooves 26, 28 and 30 preferably have the same width which may be between 1 an 2 mm. The width depends on the voltage applied.
  • the area of the circular disk 22 is preferably approximately as large as the area of the first and second ring portions 18 or 24 combined.
  • electrode signals I1 and I2 respectively are derived.
  • terminals or contact fingers 32 and 34 are provided.
  • the connecting leads are led out perpendicular to the plane of the surfaces 18, 20, 24, etc.
  • the two-electrode arrangement 18, 20 is surrounded by the protecting ring 16. Openings and recesses serve to guide the connection leads.
  • the outer circumference of both electrodes 18 and 20 is approximately equal in size to the outer circumference of the radiation cone at the place of the ionization chamber.
  • the spacing ring 8 will be attached to the lower side of the first electrode plate 6.
  • the spacing ring 8 On its upper and its lower side the spacing ring 8 has an electrically conducting outer ring surface 36, 38, respectively. These rings 36 and 38 are also grounded.
  • the second electrode plate 10 contains a second circular insulating plate 40, which may be made of the same insulating material as the first insulating plate 12.
  • the plates 12, 40 are parallel to each other.
  • the second insulating plate 40 supports on its upper side an electrically conductive outer circular ring 42. This ring 42 is electrically grounded.
  • a circular disk-shaped high voltage electrode 44 In the central portion of the upper side is located a circular disk-shaped high voltage electrode 44.
  • This electrode 44 is provided with a voltage (measured against ground) which can be between 300 and 1000 volts.
  • the high voltage electrode 44 and the first measuring electrode 18 form a first capacitor whose dielectric is determined by the gas located in the space between them.
  • the high voltage electrode 44 and the second measuring electrode 20 form a second capacitor whose dielectric is likewise determined by the gas in the space between them. These capacitors consitute two individual ionization chambers.
  • the underside or lower end face of the second insulating plate 40 is completely covered with an electrically conducting layer 46 which is grounded.
  • All the electrodes and conducting areas referenced above can preferably be made by vaporized thin layers out of an electrically conductive material.
  • 40 of alw-ninium oxide lined with silver electrodes may preferably be used. These two materials aluminum oxide and silver afford an airtight encapsulation or sealing of the measuring space 4.
  • a synthetic or plastic film or foil nonconductors 12; 40 lined with gold electrodes may preferably be used. With these substances generally an airtight sealing is hard to achieve.
  • the ionization chamber thus far described can be associated with or connected to a second chamber which measures the total average dose rate.
  • both electrode signals 11 and I2 are fed into preamplifiers 50 and 52, respectively.
  • the preamplified signals may be passed on as Monitor Signal I and Monitor Signal II, respectively, for further processing in well known manner.
  • the amplification factors of the preamplifiers 50 and 52 are assumed to be the same.
  • the preamplified signal Il is fed into an adjustable amplifier 53.
  • the amplifier 53 serves for adjusting or weighting purposes such that in case of symmetry its output signal is as large as the preamplified signal I2. If the area of the measuring electrode 18 is approximately one third the area of the measuring electrode 20, the amplification factor to be chosen should be approximately 3.
  • Both preamplified signals are sent to a comparator 54, for instance, a difference amplifier.
  • This compara- tor 54 compares the size of its two input signals. Generally this can be a difference amplifier that reacts only after a threshold has been exceeded.
  • a symmetry signal s is emitted. If symmetry prevails and if the two input signals are equal due to electronic balancing in the amplifier 53, the symmetry signal s will be zero. If symmetry no longer prevails, the symmetry signal s will be different from zero.
  • both electrode signals Il and I2 are fed into a summing or adding member 56 as well as into a subtractor or subtracting member 58.
  • an adjusting or weighting amplifier 59 Connected to the output of the subtracting member 58 is an adjusting or weighting amplifier 59.
  • the summation signal (11 + 12) and the weighted difference signal (I1 - 12) will be equal to each other in case of homogeneity or flatness.
  • Both signals are passed into another comparator 60.
  • This comparator 60 can also be a difference amplifier to which is assigned a threshold. From the output of this comparator 60 the flatness signal h1 is derived.
  • a summation signal (Il + 12) and a difference signal (Il - 12) are formed in a summation and a subtraction device 62 and 64, respectively. Subsequently these signals (Il + 12) and (I1 - 12) are subtracted from each other in a subtractor 66. The result corresponds to the signal of the total outer ring 18, 24. It is passed on to a comparator 68.
  • the difference signal (Il - 12) corresponds to the signal of the inner circular area 22.
  • This difference signal (11 - 12) is fed into an adjusting amplifier 67 for weighting.
  • the output signal of the adjusting amplifier 67 is likewise fed into the comparator 68. At the output of the comparator 68 the flatness signal h2 is produced. If a homogeneous intensity distribution prevails and if both input signals are equal to each other, it will be zero.
  • the second method -(signal h2) produces better resolution for detecting homogeneity differences than does the first method (signal hl) .
  • the output signal of the preamplifier 50 is fed into an adjustable amplifier 53.
  • This adjustable amplifier 53 serves to adjust its output signal so that when symmetry occurs this output signal is as large as the output signal of the preamplifier 52.
  • the signal Il will be approximately one third the size of the signal 12. This means that the amplifier 53 has to amplify the output signal of the preamplifier 50 by approximately a factor of 3 so that its output signal is approximately the same as the output signal of the preamplifier 52.
  • the asymmetrical intensity distribution of the curve a in Fig. 1 prevails along the line Y-Y in Fig. 3, whereby the rim region of stronger intensity (right rim as illustrated) lies on the second measuring electrode 20.
  • the first measuring electrode 18 provides a smaller output signal Il as compared with the symmetrical case of curve g, while the second measuring electrode 20 produces a larger output signal I2.
  • the input signal at the negative input of the comparator 54 is larger than the input signal at the positive input. Consequently, the symmetry signal a is now negative.
  • the polarity (+ or - sign) of the symmetry signal s indicates in which direction an asymmetry prevails.
  • the nonhomogeneous signal il of Fig. 1 prevails along the line X-X in Fig. 3.
  • the circular disk 22 (area factor 2) receives a larger intensity than the first ring portion 18 (area factor 1) and the second ring portion 24. Consequently the measuring signal I2 has increased with respect to the measuring signal Il of the first electrode 18 when compared to the case of uniform distribution of intensity g. Consequently percentage of the output signal of the amplifier 59 has gained with respect to the output signal of the addition element 56.
  • the input signal which has been delivered by the adjustable amplifier 59 will prevail so that there results a negative flatness signal hl. This is an indication that the X-ray radiation cone or the electron beam of the linear accelerator is no longer homogeneous.
  • the second measuring signal 12 is here again larger than the first measuring signal I1 by a factor of 3.
  • the addition of both signals I1, I2 in the addition element 62 produces a corresponding sum signal (Il + 12), while the subtraction in the subtractor 64 produces a corresponding difference signal (I2 - I1).
  • the output signals of- the componenets 66 and 67 are equal to each other. This is determined by the comparator 68.
  • Fig. 5 an embodiment of the two-electrode arrangement is shown in which the first ring portion 18 is shorter along its periphery than the second ring portion 24. In this case also both ring portions 18, 24 combined extend to an angle of approximately 360°. In particular, the sector of the first ring electrode 18 covers approximately 180°. In the illustrated example an angle of 157.5° was chosen. Thus, two radially extending separation grooves 26, 28 are located at 0° and 157.5°, respectively. The function of this two-electrode arrangement is similar to that of Fig. 3.

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  • Measurement Of Radiation (AREA)
EP82106592A 1981-08-03 1982-07-21 Chambre dosimètre pour électron et rayonnement X Expired EP0071826B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US289137 1981-08-03
US06/289,137 US4427890A (en) 1981-08-03 1981-08-03 Dose monitor chamber for electron or X-ray radiation

Publications (3)

Publication Number Publication Date
EP0071826A2 true EP0071826A2 (fr) 1983-02-16
EP0071826A3 EP0071826A3 (en) 1983-08-03
EP0071826B1 EP0071826B1 (fr) 1985-10-23

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Family Applications (1)

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EP82106592A Expired EP0071826B1 (fr) 1981-08-03 1982-07-21 Chambre dosimètre pour électron et rayonnement X

Country Status (4)

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US (1) US4427890A (fr)
EP (1) EP0071826B1 (fr)
CA (1) CA1180470A (fr)
DE (1) DE3267023D1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2570908A1 (fr) * 1984-09-24 1986-03-28 Commissariat Energie Atomique Systeme de traitement des signaux electriques issus d'un detecteur de rayons x
DE3844716C2 (de) * 1987-08-24 2001-02-22 Mitsubishi Electric Corp Partikelstrahlmonitorvorrichtung

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4882566A (en) * 1988-08-03 1989-11-21 Hill-Rom Company, Inc. Safety control system for a hospital bed
US5072123A (en) * 1990-05-03 1991-12-10 Varian Associates, Inc. Method of measuring total ionization current in a segmented ionization chamber
US5120967A (en) * 1991-01-25 1992-06-09 The United States Of America As Represented By The Secretary Of The Air Force Apparatus for direct measurement of dose enhancement
CA2159531A1 (fr) * 1995-09-29 1997-03-30 Courtland B. Lawrence Methode pour surveiller la dose absorbee par la cible d'un faisceau d'electrons
US5672878A (en) * 1996-10-24 1997-09-30 Siemens Medical Systems Inc. Ionization chamber having off-passageway measuring electrodes
US6762418B2 (en) 2001-03-13 2004-07-13 Advanced Cardiovascular Systems, Inc. Calorimetry as a routine dosimeter at an electron beam processing facility
DE102007014723A1 (de) * 2007-03-23 2008-11-27 Gesellschaft für Schwerionenforschung mbH (GSI) Bestimmung eines Planungsvolumens für eine Bestrahlung eines Körpers
JP4691587B2 (ja) 2008-08-06 2011-06-01 三菱重工業株式会社 放射線治療装置および放射線照射方法
GB2571124A (en) * 2018-02-19 2019-08-21 Elekta ltd Method and apparatus for beam energy measurement
CN108303723A (zh) * 2018-04-16 2018-07-20 广东省建筑工程机械施工有限公司 一种热室剂量探测器套管结构

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2215701A1 (fr) * 1973-01-26 1974-08-23 Cgr Mev
US3852610A (en) * 1973-02-26 1974-12-03 Varian Associates Transmission ion chamber
GB1598962A (en) * 1978-03-21 1981-09-30 Siemens Ag Arrangement for detecting radiation
EP0040589A2 (fr) * 1980-04-23 1981-11-25 Instrument AB Scanditronix Procédé et dispositif utilisant une chambre d'ionisation à transmission

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2215701A1 (fr) * 1973-01-26 1974-08-23 Cgr Mev
US3852610A (en) * 1973-02-26 1974-12-03 Varian Associates Transmission ion chamber
GB1598962A (en) * 1978-03-21 1981-09-30 Siemens Ag Arrangement for detecting radiation
EP0040589A2 (fr) * 1980-04-23 1981-11-25 Instrument AB Scanditronix Procédé et dispositif utilisant une chambre d'ionisation à transmission

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2570908A1 (fr) * 1984-09-24 1986-03-28 Commissariat Energie Atomique Systeme de traitement des signaux electriques issus d'un detecteur de rayons x
DE3844716C2 (de) * 1987-08-24 2001-02-22 Mitsubishi Electric Corp Partikelstrahlmonitorvorrichtung

Also Published As

Publication number Publication date
CA1180470A (fr) 1985-01-02
EP0071826A3 (en) 1983-08-03
DE3267023D1 (en) 1985-11-28
EP0071826B1 (fr) 1985-10-23
US4427890A (en) 1984-01-24

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