WO2011050822A1 - Appareil de radiothérapie - Google Patents

Appareil de radiothérapie Download PDF

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Publication number
WO2011050822A1
WO2011050822A1 PCT/EP2009/007641 EP2009007641W WO2011050822A1 WO 2011050822 A1 WO2011050822 A1 WO 2011050822A1 EP 2009007641 W EP2009007641 W EP 2009007641W WO 2011050822 A1 WO2011050822 A1 WO 2011050822A1
Authority
WO
WIPO (PCT)
Prior art keywords
pulse
pulses
pattern
sequence
radiotherapeutic apparatus
Prior art date
Application number
PCT/EP2009/007641
Other languages
English (en)
Inventor
Kevin Brown
Adrian Maxwell Smith
Original Assignee
Elekta Ab (Publ)
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Elekta Ab (Publ) filed Critical Elekta Ab (Publ)
Priority to PCT/EP2009/007641 priority Critical patent/WO2011050822A1/fr
Priority to EP10779221.0A priority patent/EP2493567B9/fr
Priority to US13/503,478 priority patent/US8995617B2/en
Priority to PCT/EP2010/005988 priority patent/WO2011050887A1/fr
Publication of WO2011050822A1 publication Critical patent/WO2011050822A1/fr

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Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N5/1042—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N5/1042—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head
    • A61N5/1045—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head using a multi-leaf collimator, e.g. for intensity modulated radiation therapy or IMRT
    • A61N5/1047—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head using a multi-leaf collimator, e.g. for intensity modulated radiation therapy or IMRT with movement of the radiation head during application of radiation, e.g. for intensity modulated arc therapy or IMAT

Definitions

  • the present invention relates to radiotherapeutic apparatus. BACKGROUND ART
  • the dose rate was relatively unimportant, and accelerator designs tended to work with a fixed Pulse Repetition Frequency (PRF) at which the RF source was pulsed in order to create radiation pulses.
  • PRF Pulse Repetition Frequency
  • the base frequency could be halved, repeatedly if necessary.
  • the apparatus generated fixed dose rates at fixed divisors e.g. Vz, V4, ... of the maximum output power, corresponding to like fractions of the base frequency.
  • This limitation also causes step changes in other machine parameters, such as the gantry speeds and leaf speeds. This causes a reduction in delivery accuracy, because the servo systems must compensate for gross changes in demand.
  • the present invention therefore provides radiotherapeutic apparatus comprising a source of radiation able to issue pulses of radiation at a base frequency, and a control apparatus in which are defined a plurality of suppression patterns each of which controls every n t pulse that is not controlled by a pattern with a higher value of n, wherein n is different for each pattern, each pattern being selectable independently.
  • a control apparatus in which are defined a plurality of suppression patterns each of which controls every n t pulse that is not controlled by a pattern with a higher value of n, wherein n is different for each pattern, each pattern being selectable independently.
  • n 2 p where p is a positive integer.
  • the present invention also provides a radiotherapeutic apparatus comprising a source of radiation able to issue pulses of radiation at a base frequency, and a control apparatus arranged to permit pulses provided these match a putse pattern chosen to achieve a selected time-averaged power level, the chosen pulse pattern being one selected from a plurality of pulse patterns that include patterns consisting of trains of pulses that include, relative to the base frequency, at least every n th and every m th pulse where n ⁇ m.
  • such an apparatus issues a pulse if it is the n th or the m th or the k th (etc) where both the values of the repetition rates n, m, k... and the number of repetitions are selectable independently. So in the above example, the odd pulses, every 2 nd , and every 8 th pulse are included in order to give a 7/8 ths output.
  • the pulse pattern can be obtained by resolving the selected power level as an integer representable as a binary number, and then inserting an n th pulse if the binary number has a 1 digit at the q th power of 2 where q is the n th digit of the binary carry sequence.
  • the binary carry sequence can be repeated modulo the number of possible output power levels, assuming that the selected power level is one selected from a range of possible output power levels.
  • the q sequence would be 0, 1, 0, 2, 0, 1, 0, 3, and then repeating.
  • control apparatus can be a memory in which a table is retained, the table containing the sequence of pulses to be issued.
  • the table can be freshly populated with a sequence when a power level is selected, or the table can contain sequences for a plurality of (preferably all the) power levels and the control unit can be adapted to select a desired sequence.
  • control apparatus may be implemented in digital logic to implement the shift and decode operations necessary to implement the patterns.
  • the output power level of the apparatus we refer interchangeably to the output power level of the apparatus, and the dose rate that is delivered to the patient.
  • the pulses produced by the apparatus essentially represent a mean power level in the magnetron, which is converted to an RF output into the linear accelerator, which is converted to a radiation dose.
  • the output power level and the dose rate are therefore equivalent terms insofar as this invention is concerned.
  • FIG. 1 illustrates the variable output powers available
  • FIGS. 1a to 2c illustrate known forms of pulsed output
  • FIG. 3 illustrates the pulsed outputs of figure 2 schematically
  • Figure 4 illustrates the pulsed outputs of the present invention graphically
  • Figure 5 shows a pulsed output modulo 256.
  • Figure 1 illustrates the problem addressed by the present invention. It plots the desired output power along the x axis 10 versus the actually obtained output power along the y axis 12.
  • the ideal behaviour would of course be a 1 : 1 straight line as illustrated at 14.
  • known systems are far less linear than this.
  • V2 power 16, 1 A power 18 and Vs power 20 (etc) and as it is important not to overdose a patient, if the desired power is between one of these levels then the lower level must be adopted and the treatment time extended correspondingly (or another form of compensation applied). This results in behaviour according to the line 24, which (unsurprisingly) becomes very non-linear at higher power levels.
  • the present invention smoothes this behaviour by allowing the selection of intermediate fractions of the maximum power level.
  • it permits the adoption of any level n/2 (where n and / are positive integers and n ⁇ i).
  • n/2 where n and / are positive integers and n ⁇ i.
  • Figures 2a to 2c show the effect of figure 1 on the actual output power of a known device.
  • Figure 2a shows the output at maximum power; this consists of a stream of output pulses 28 spaced according to the base frequency. It should be noted that for reasons of clarity the pulses are shown with an exaggerated width relative to the spacing between them; in practice the pulses have a width about 3 orders of magnitude less than their time separation, typically a 2.5 microsecond pulse every 2.5 milliseconds.
  • Figure 2b shows the selection of V2 power, resulting in the omission of every other pulse. The time- averaged power of the remaining pulses 30 is therefore half that of the pulses 28. As the pulse rate is very high (typically 400-500 Hz) it is the average over many pulses that matters.
  • Figure 2c shows a further frequency division, to 1 A power, leaving only every fourth pulse 32 from the pulse train 28 of figure 2a.
  • Figure 3 shows a graphical representation of the frequency division shown in figures 2a to 2c.
  • a horizontal line 34 of adjacent blocks 36 denotes a steady stream of pulses at the base frequency, i.e. full power.
  • the next line 38 below line 34 denotes the next lower power level, and consists of a stream of pulses 40 which omits every other pulse.
  • line 42 illustrates the next lower power level, in which one pulse in 4 remains.
  • Line 44 shows one pulse in 8
  • lines 46, 48 and 50 show one pulse in 16, 32 and 64 respectively.
  • the present invention employs a technique known as "Bit Rate Multiplying" to maintain all the design criteria discussed above (and the benefits thereof) while achieving a higher resolution of PRF variation and therefore dose rates.
  • the stream of pulses in the desired output pulse stream differs from the stream of pulses at the base frequency in that some pulses are absent from the output stream.
  • the output stream can thus be characterised by the pulses that are absent, or by the pulses that are present. This corresponds to an engineering choice between suppressing pulses, or permitting them.
  • the invention requires the suppression of pulses according to a number of patterns.
  • a user can then be allowed to select any, some or all of the individual suppression patterns, in any combination.
  • the effect of this is shown by way of example in figure 4, in the form of a modulo 64 pattern (therefore offering 64 power levels). This is set out in the same manner as figure 3. At the highest power level 52, all pulses are present and no pulses from the base frequency are suppressed. The device is therefore operating at full power.
  • the 64 th pulse 58 remains in place as, although it is the 32 nd pulse after the omitted 32 nd pulse 56, it is controlled by a higher pattern.
  • the power level immediately below the 63/64 ths level, i.e. the 62/64 ths power level 58 is then obtained by selecting just the "one in 16" pattern. This suppresses the 16 th and the 48 th pulse, but leaves the 32 nd and 64 th pulses in place as these are controlled by patterns with a higher value of n - i.e. the "one in 32" and "one in 64" patterns. The result is that only two pulses in every 64 are omitted, giving 62 pulses out of a possible 64.
  • a power level of 61/64 ths can then be obtained by selecting both the "one in 32" pattern and also the "one in 16” pattern. This omits the 16 th , 32 nd and 48 th pulses, leaving the 64 th pulse 58 present.
  • the sequence can then continue, selecting and deselecting patterns as necessary to achieve a specific power level.
  • the application of these simple (and hence easily computable) rules allows the selection of any of 2' evenly spaced power levels.
  • the resulting pulse patterns are generally evenly spaced, retaining the necessary thermal stability.
  • the base frequency is retained, and the patterns of omitted pulses are deterministic and predictable. Thus, all the necessary advantages of the prior system are retained but the power levels are spread evenly.
  • the desired power level can in fact be chosen as a binary number - for the above 64-level (6-bit) system this will be between 000000 and 111111.
  • the value chosen for these bits then configures the output pulse pattern; each pattern is controlled by one bit.
  • MSB leftmost (most-significant) bit
  • LSB right-most (least-significant) bit
  • radiotherapeutic apparatus uses a PRF timing generator to create RF trigger pulses and related signals that drive the creation of an output pulse.
  • the design of the PRF timing generator will therefore use this pattern to blank selected RF trigger pulses (etc) and therefore blank (or suppress) the creation of a radiation pulse.
  • the white areas in the pattern indicate the absence of an RF pulse and therefore the absence of a radiation pulse.
  • This technique produces an optimal pattern.
  • this pattern can replicate the previous known divisors ⁇ Vi, 1 ⁇ 4 etc) but in between these there is a set of deterministic, optimally spaced pulse patterns which create a set of finer pulse repetition frequencies.
  • this technique therefore a) continues to allow the electron gun current to be synchronised with the pulse repetition frequency as above. b) Allows the selection of dose rates to a finer resolution in addition to the classic V2, 1 ⁇ 4, divisors. c) Produces a pulse pattern that continues to offer the benefits of thermal equilibrium by optimally spacing the pulses in the time domain. d) Produces a deterministic pattern that allows the prediction of the pulse position given a single number m and a reference pulse. This enables synchronised imaging schemes to continue to work.
  • the PRF timing generator can decide whether to allow a particular pulse by running the relevant algorithm, using appropriate digital logic to produce the sequence as per the algorithm in real time and output a control signal that is used to produce or suppress individual pulses. If this approach is considered too computationally intensive, then an alternative solution may be to calculate the results of the algorithm when the power level is set and store the results in a lookup table which the PRF timing generator can consult for each pulse.
  • the lookup table could include the patterns for all available power levels, and the PRF timing generator could consult the appropriate part of the table, such as one specific line corresponding to the chosen power level.
  • the relevant rule is that the pulse pattern is one that consists of at least one train of pulses that include, relative to the base frequency, at least every n t pulse. Multiple such trains can be superimposed, i.e. also including every m th pulse and/or every k th pulse (etc), where n ⁇ m ⁇ k.
  • such an apparatus issues a pulse if it is the n th or the m th or the k th (etc) where both the values of the repetition rates n, m, k... and the number of repetitions are selectable independently. So, for example, the odd pulses, every 2 nd , and every 8 th pulse can be included in order to give a 7/8 ths output.
  • the pulse pattern can be obtained by resolving the selected power level as an integer (which will therefore be representable as a binary number), and then inserting an n th pulse if the binary number has a 1 digit at the q th power of 2 where q is the n th digit of the binary carry sequence.
  • the binary carry sequence can be repeated modulo the number of possible output power levels.
  • the q sequence would be 0, 1, 0, 2, 0, 1, 0, 3, and then repeating. This gives, in practice, a pattern identical to that of figure 4.
  • the choice between the two possible approaches is therefore one of engineering and/or programming convenience.
  • a further alternative approach to the invention is to generate the pattern of allowed and non-allowed pulses through code.
  • a example of a straightforward program in MatlabTM scripting language able to produce the pattern to a desired modulo would be: clear
  • position (:, i) position (:, i) *binaryfield (:, i) ;
  • bitstream(i) 0;
  • a modulo 256 pattern should be used as shown in figure 5. This is arbitrary and could be larger or smaller. It does however allow the correct dose rate granularity to be achieved, essentially 256 unique dose rates. In principle, any number could be selected; a higher number will offer finer control of the power output, but this may not be necessary in practice.
  • a modulo 256 pattern used on apparatus with a 400Hz base frequency will repeat every 256/400 seconds, i.e. 0.64 seconds.
  • a modulo 4096 pattern would repeat every 4096/400 seconds, i.e. slightly over 10 seconds. In practice, this is of little use for techniques such as VMAT, in which it is unlikely that the apparatus will be operating at a constant dose rate for over 10 seconds.
  • a modulo 256 pattern is therefore a compromise, which approximates to a continuous adjustment with a degree of granularity that is small enough to be of little or no concern. In practice, a modulo of between 2 6 and 2 10 is likely to offer a useful compromise.

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  • Health & Medical Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Biomedical Technology (AREA)
  • Pathology (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Radiation-Therapy Devices (AREA)

Abstract

La capacité de faire varier, de façon fine, la résolution au niveau du débit de dose d'un appareil de radiothérapie permet une diminution significative des durées d'application d'une radiothérapie VMAT et des techniques associées. L'appareil de radiothérapie de la présente invention comprend une source de rayonnement capable d'émettre des impulsions de rayonnement selon une fréquence de base, et un appareil de commande conçu pour permettre que les impulsions ainsi émises correspondent à un modèle d'impulsions choisi pour que puisse être atteint un niveau de puissance moyenné en temps sélectionné. Le modèle d'impulsions choisi est sélectionné au sein d'une pluralité de modèles d'impulsions qui comprennent des modèles constitués de trains d'impulsions comportant, par rapport à la fréquence de base, au moins chaque nième et mième impulsion lorsque n ≠ m. Un tel appareil émet, essentiellement, une impulsion s'il s'agit de la nième ou de la mième ou de la kième (etc.), chaque fois que n, m, k… peuvent être sélectionnés de façon indépendante. Le modèle d'impulsions peut être obtenu par la résolution du niveau de puissance sélectionné en tant que nombre entier pouvant être représenté sous la forme d'un nombre binaire, puis par l'insertion d'une nième impulsion si le nombre binaire possède un chiffre à la puissance qième de 2, q étant le nième chiffre de la séquence porteuse binaire. La séquence porteuse binaire peut être un modulo répété du nombre de niveaux de puissance de sortie possibles, si l'on part du principe que le niveau de puissance choisi est sélectionné au sein d'une plage de niveaux de puissance de sortie possibles. L'appareil de commande peut comporter une mémoire dans laquelle est stocké un tableau, ledit tableau contenant la séquence d'impulsions devant être émises. Ce tableau peut être fraîchement rempli d'une séquence lorsqu'un niveau de puissance est sélectionné, ou le tableau peut contenir des séquences pour une pluralité de niveaux de puissance (de préférence pour tous), et l'unité de commande peut être conçue pour sélectionner une séquence désirée.
PCT/EP2009/007641 2009-10-26 2009-10-26 Appareil de radiothérapie WO2011050822A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
PCT/EP2009/007641 WO2011050822A1 (fr) 2009-10-26 2009-10-26 Appareil de radiothérapie
EP10779221.0A EP2493567B9 (fr) 2009-10-26 2010-10-01 Appareil de radiothérapie
US13/503,478 US8995617B2 (en) 2009-10-26 2010-10-01 Radiotherapeutic apparatus
PCT/EP2010/005988 WO2011050887A1 (fr) 2009-10-26 2010-10-01 Appareil de radiothérapie

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Application Number Priority Date Filing Date Title
PCT/EP2009/007641 WO2011050822A1 (fr) 2009-10-26 2009-10-26 Appareil de radiothérapie

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20130259198A1 (en) * 2010-11-28 2013-10-03 Tel Hashomer Medical Research Infrastructure And Services Ltd. Method and system for electron radiotherapy
EP3124078A1 (fr) * 2015-07-27 2017-02-01 Elekta Limited Procédé de commande et appareil de radiothérapie amélioré

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007124760A1 (fr) * 2006-04-27 2007-11-08 Elekta Ab (Publ) Appareil radiothérapeutique
US20090121155A1 (en) * 2007-11-09 2009-05-14 Elekta Ab (Publ) Radiotherapy apparatus and parts thereof
US20090154650A1 (en) * 2007-12-13 2009-06-18 Aet, Inc. X-ray generator

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007124760A1 (fr) * 2006-04-27 2007-11-08 Elekta Ab (Publ) Appareil radiothérapeutique
US20090121155A1 (en) * 2007-11-09 2009-05-14 Elekta Ab (Publ) Radiotherapy apparatus and parts thereof
US20090154650A1 (en) * 2007-12-13 2009-06-18 Aet, Inc. X-ray generator

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20130259198A1 (en) * 2010-11-28 2013-10-03 Tel Hashomer Medical Research Infrastructure And Services Ltd. Method and system for electron radiotherapy
US9711253B2 (en) * 2010-11-28 2017-07-18 Tel Hashomer Medical Research Infrastructure And Services Ltd. Method and system for electron radiotherapy
EP3124078A1 (fr) * 2015-07-27 2017-02-01 Elekta Limited Procédé de commande et appareil de radiothérapie amélioré
CN106390305A (zh) * 2015-07-27 2017-02-15 医科达有限公司 改进的放射治疗设备和方法
CN106390305B (zh) * 2015-07-27 2021-02-02 医科达有限公司 改进的放射治疗设备和方法

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