EP0322656A1 - Assembly and method for monitoring the lateral position of a beam of ionizing radiation - Google Patents

Assembly and method for monitoring the lateral position of a beam of ionizing radiation Download PDF

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Publication number
EP0322656A1
EP0322656A1 EP88120939A EP88120939A EP0322656A1 EP 0322656 A1 EP0322656 A1 EP 0322656A1 EP 88120939 A EP88120939 A EP 88120939A EP 88120939 A EP88120939 A EP 88120939A EP 0322656 A1 EP0322656 A1 EP 0322656A1
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EP
European Patent Office
Prior art keywords
chamber
axis
electrodes
along
electrode
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.)
Withdrawn
Application number
EP88120939A
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German (de)
English (en)
French (fr)
Inventor
Norbert Barthelmes
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
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Siemens AG
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Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Publication of EP0322656A1 publication Critical patent/EP0322656A1/en
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01TMEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16Measuring radiation intensity
    • G01T1/185Measuring radiation intensity with ionisation chamber arrangements
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J47/00Tubes for determining the presence, intensity, density or energy of radiation or particles
    • H01J47/02Ionisation chambers

Definitions

  • the invention relates to a device and a method for monitoring a beam of ionizing radiation and, more particularly, to a beam steering system including a transmission ion chamber assembly for detecting the lateral position of such a beam.
  • transmission ion chambers In various applications, especially in radiotherapy, it is necessary to monitor the actual beam position and to correct any deviations from the intended beam position. To do this, a number of devices - called transmission ion chambers - have been developed.
  • Medical Physics 11 (1984), pages 105 to 128, section VI.B. discloses a multi-chamber construction of five parallel plates alternately carrying high voltage (polarizing) electrodes and ion-trapping (collecting) electrodes. Each collecting electrode is divided into four sectors such that four distinct laminar collecting volumes are designed. By summing and subtracting the current signals of specific sector pairs, the beam dose and position are measured. For correcting misalignments, the position signals are used to energize beam steering coils grouped around an electron beam.
  • the beam position is determined by sensing the differences between signals derived from different beam areas.
  • the chamber must therefore be struck by a large beam cross-section, i.e. placed downstream of all the beam widening (and weakening) elements.
  • the signal and in particular the signal to noise ratio are weak and require a sophisticated signal processing system to obtain an acceptable sensitivity.
  • the chamber cannot be utilized in instances where the radiation field is built up by scanning rather than spreading the beam.
  • the chamber assembly contains a multitude of electrodes and provides a plurality of signals, it is mechanically complicated and large numbers of electronic components are required to produce it.
  • beams for example, electron or x-ray beams
  • beam diameters for example, swept or diffused beams
  • Each chamber has an upstream base wall, a downstream base wall and a sidewall spacing both base walls; and contains a pair of electrodes, a collector electrode and an high voltage (HV) electrode.
  • Both electrodes are separated from each other by a distance which varies gradually along a chamber-specific measuring axis and, preferably, over the entire electrode extension along this axis.
  • HV high voltage
  • Both chambers When both chambers are in place, their measuring axes form angles with the beam path as well as between each other.
  • Means are provided to extract from the collector electrodes current signals in dependence upon the beam position along the associated measuring axis.
  • Each ion chamber contains gas which is ionized when hit by a beam of ionizing radiation. Gas electrons will migrate to the positive electrode, and the gas ions will be trapped at the negative electrode.
  • the amplitude of the ion current which is normally used to provide the signal, depends upon a, variety of parameters, essentially the kind of ionizing radiation, the type of the filling gas, the gas pressure, the voltage drop between the electrodes and the irradiated gas volume. Since the full beam is intercepted by the electrodes, the cross-section of the irradiated gas volume corresponds to the beam cross-section and is therefore virtually constant.
  • the current signal is basically a function of the distance between the electrodes and in practice, varies roughly linearly with it. Consequently, if, as here, the electrode distance varies along a certain axis, the signal amplitude reflects the beam position along this axis, so that by using two crossed chambers the beam position in a plane perpendicular to the beam axis may be detected.
  • the distance between the collecting electrode and the HV electrode varies linearly across the entire length of these electrodes, and the measuring axes extend perpendicular to the beam axis, as well as to each other.
  • the beam can strike the cell electrodes with its entire cross-section, regardless of the degree of its misalignment.
  • the electrodes are, preferably, at least twice as large as the beam cross-section.
  • the chamber may still be more compact than conventional types, since it can be placed just downstream of the first beam-widening element.
  • the two chambers contain electrode plates, i.e. substrates coated with conductive layers, and share one electrode plate.
  • each current signal is typically processed such that it energizes a pair of steering coils located at opposite sides of the electron beam.
  • a signal processing unit in which each current signal is first amplified in an amplifier and than subtracted from a reference signal in a comparator.
  • the reference signal is furnished by a reference signal source; its value corresponds to the amplitude the amplified signal would have if the beam were centered.
  • the comparator output signal which is indicative of the beam misalignment along the associated measuring axis, is fed into a driver unit which controls the current through the pair of steering coils.
  • a method for detecting the lateral displacement of a beam of ionizing radiation is to direct the beam through two activated transmission ion chambers, each containing a collecting electrode and a high voltage electrode. The distance between both electrodes varies gradually along a chamber-specific measuring axes, and both axes are perpendicular to the beam axis as well as to each other. Then, current signals are derived from the collector electrodes. These signals correspond to the beam position along the associated measuring axis.
  • This method could be expanded to correct beam misalignments by simply transforming each current signal into an error signal which is indicative of the beam displacement along the associated measuring axis, and by using this error signal to energize a pair of beam steering coils surrounding the beam.
  • Fig. 1 shows a LINAC with a bending magnet 1 which projects an electron beam 2 through a window 3 along a beam axis 4.
  • the beam which is actually pulsed with a pulse length of several usec and a pulse repetition rate of a few milliseconds, has a diameter of about 1 millimeter and comprises electrons in the range of 10 MeV.
  • beam 2 hits a target 5 which produces an x-ray beam.
  • This beam is shaped in a shielding block 6 and in a jaw system comprised of two pairs of opposite jaws 7, 8 and 9. Between target 5 and shielding block 6 there is disposed a chamber assembly 10.
  • Chamber assembly 10 comprises, as shown in Figs. 2 and 3, three plates 11, 12 and 13. These plates are spaced from each other by spacer rings 14, 15. The outer plates are tilted against the central plate so that their distance varies linearly along measuring axes 33 and 34, respectively. Both axis are, as can be seen from the figures orthogonal to each other in a plane perpendicular to the beam axis 4. Outer plates 11, 13 are coated on their inner sides with conductive layers serving as collecting electrodes l6, 17, and the central plate 12 carries on each side a conductive layer each serving as a high voltage electrode 18, 19.
  • Each part of chamber assembly 10 can be made of conventional material.
  • the plates may consist of a polyester known under the trademark Capton and may have a thickness of several mil.
  • the electrodes may be sputtered gold layers.
  • the cell defined by the plates and spacer rings may be filled with air.
  • Such an assembly has a very low self-absorption for gamma rays as well as electron beams.
  • the polyester foils from being bent, i.e. the distances between corresponding electrodes from being altered, by atmospheric temperature and/or pressure changes, the cells communicate with the environment through (not shown) openings in the spacer rings. Any fluctuations in these parameters are electronically compensated. The means by which this is achieved is known to persons skilled in the art and has therefore not been shown.
  • the chamber assembly is part of a feed-back system for correcting the beam position.
  • the HV electrodes 18, 19 are connected to a high voltage source 20.
  • the signals which are derived from the collecting electrodes 16, 17 and represent the amount of ions produced by one of the beam pulses, are amplified in amplifiers 21, 22 and then subtracted from reference signals in comparators 23, 24.
  • the reference signals are furnished by reference signal supplies 25 or 26.
  • the value of the reference signals equals the amplitude the amplified signals would have in case the beam were aligned. They depend upon the actual beam intensity which is independently measured and communicated to the supplies 25, 26.
  • the difference between the amplified signal and the reference signal controls, via a driver stage 27, 28, the current in a pair of steering coils 29, 30, 31 and 32 which are located on opposite sides of the electron beam 2 before it is diverted in the bending magnet 1.
  • This current creates at the beam a transverse magnetic field which exerts a correcting force perpendicular to the beam axis and the field direction. It is varied such that the difference signal disappears, i.e. the beam becomes aligned.
  • an electron rather than an x-ray beam could be monitored.
  • the incident beam is much more intensive but also spread over a larger solid angle so that the gas could, if necessary, easily be kept below its saturation region, for example by lowering the high voltage.
  • the distance between corresponding electrodes vary according to a non-linear function or with a profile having an extremum at the ideal beam position. The latter does not require a reference signal and affords a simple measurement of the overall beam intensity. It is also possible to use the electrons rather than the ions of the ionized gas for generating the current signal.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Molecular Biology (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Measurement Of Radiation (AREA)
  • Particle Accelerators (AREA)
  • Radiation-Therapy Devices (AREA)
  • Electron Tubes For Measurement (AREA)
EP88120939A 1987-12-28 1988-12-14 Assembly and method for monitoring the lateral position of a beam of ionizing radiation Withdrawn EP0322656A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US138759 1987-12-28
US07/138,759 US4803368A (en) 1987-12-28 1987-12-28 Assembly and method for monitoring the lateral position of a beam of ionizing radiation

Publications (1)

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EP0322656A1 true EP0322656A1 (en) 1989-07-05

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EP88120939A Withdrawn EP0322656A1 (en) 1987-12-28 1988-12-14 Assembly and method for monitoring the lateral position of a beam of ionizing radiation

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US (1) US4803368A (ja)
EP (1) EP0322656A1 (ja)
JP (1) JPH01223384A (ja)

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JPH11233436A (ja) * 1997-12-10 1999-08-27 Canon Inc X線照明装置及び方法、並びにこれを用いたx線露光装置やデバイス製造方法
GB2350891B (en) * 1999-06-12 2001-04-18 Medical Res Council X-ray beam position monitors
WO2008006198A1 (en) 2006-07-10 2008-01-17 University Health Network Apparatus and methods for real-time verification of radiation therapy
TWI315540B (en) * 2006-07-28 2009-10-01 Iner Aec Executive Yuan Penetration ionization chamber
US7651270B2 (en) * 2007-08-31 2010-01-26 Rigaku Innovative Technologies, Inc. Automated x-ray optic alignment with four-sector sensor
US8933421B2 (en) * 2008-04-21 2015-01-13 Varian Medical Systems Particle Therapy Gmbh Halo monitor in rotatable gantry for particle beam positioning
JP5687265B2 (ja) * 2009-03-20 2015-03-18 イオン・ビーム・アプリケーションズ・エス・アー ハドロンビームの線量測定モニタリング用のデバイス及びハドロンビームをモニタリングするための方法
BE1018836A3 (fr) * 2009-07-24 2011-09-06 Ion Beam Applic Sa Dispositif et methode pour la mesure d'un faisceau energetique.
JP2013506823A (ja) * 2009-10-01 2013-02-28 イオン・ビーム・アプリケーションズ・エス・アー エネルギービームのライン制御装置および方法
US20110095199A1 (en) * 2009-10-27 2011-04-28 Institute Of Nuclear Energy Research Atomic Energy Council, Executive Yuan Method to measure current using parallel plate type ionization chamber with the design of guard electrode
US9739892B2 (en) 2014-04-09 2017-08-22 Phenix Medical Llc Fast, high-rate, position-sensitive absolute dosimeter for ion beam therapy
US11385360B2 (en) * 2015-06-05 2022-07-12 University Health Network Sensors with virtual spatial sensitivity for monitoring a radiation generating device
US10122946B2 (en) * 2015-11-11 2018-11-06 Fei Company Method for detecting particulate radiation
US10879028B2 (en) * 2016-04-14 2020-12-29 Varian Medical Systems, Inc. Beam position monitors for medical radiation machines
EP3460530B1 (en) 2017-09-20 2022-03-30 Ion Beam Applications S.A. One dimensional transmission detector for radiotherapy
GB2571124A (en) * 2018-02-19 2019-08-21 Elekta ltd Method and apparatus for beam energy measurement

Citations (3)

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Publication number Priority date Publication date Assignee Title
US3955089A (en) * 1974-10-21 1976-05-04 Varian Associates Automatic steering of a high velocity beam of charged particles
US3997788A (en) * 1974-06-14 1976-12-14 C.G.R.-Mev. Device for monitoring the position, intensity, uniformity and directivity of an ionizing radiation beam
EP0040589A2 (en) * 1980-04-23 1981-11-25 Instrument AB Scanditronix A method and a device relating to a transmission ion chamber

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US2917647A (en) * 1955-08-01 1959-12-15 Fowler Ivan Landen Geiger-muller type counter tube
FR2133318A5 (ja) * 1971-04-16 1972-11-24 Thomson Csf
FR2134296B1 (ja) * 1971-04-30 1974-03-22 Thomson Csf
FR2215701B1 (ja) * 1973-01-26 1978-10-27 Cgr Mev
US4206355A (en) * 1975-02-07 1980-06-03 C.G.R. Mev System for monitoring the position intensity uniformity and directivity of a beam of ionizing radiation
US4131799A (en) * 1977-04-01 1978-12-26 Applied Radiation Corporation Ionization chamber

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3997788A (en) * 1974-06-14 1976-12-14 C.G.R.-Mev. Device for monitoring the position, intensity, uniformity and directivity of an ionizing radiation beam
US3955089A (en) * 1974-10-21 1976-05-04 Varian Associates Automatic steering of a high velocity beam of charged particles
EP0040589A2 (en) * 1980-04-23 1981-11-25 Instrument AB Scanditronix A method and a device relating to a transmission ion chamber

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
NUCLEAR INSTRUMENTS AND METHODS IN PHYSICS RESEARCH, vol. 228, no. 1, December 1984, pages 45-50, Elsevier Science Publishers B.V., AmsterdamNL; J.A. BLISSETT et al.: "Development of a prototype tapered cell drift chamber" *

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US4803368A (en) 1989-02-07
JPH01223384A (ja) 1989-09-06

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