throbber
‘United States Patent
`
`
`3,906,233
`
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`
`
`
`[451 Sept. 16, 1975
`Vogel
`
`[191
`
`
`
`[111
`
`[54] SYSTEM AND METHOD FOR
`
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`
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`ADNIINISTERING RADIATION
`
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`lnventor: Thomas M. Vogel, Sunnyvale, Calif.
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`[73] Assignee: Varian Associates, Palo Alto, Calif.
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`
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`Oct. 12, 1973
`Filed:
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`[21] Appl. No.: 406,080
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`[75]
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`[22]
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`[52] U.S. Cl................................ .. 250/355; 250/354
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`[51]
`Int. Cl. ............................................ .. G0lt 1/17
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`[58] Field of Search ............. .. 250/354, 355, 445 T
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`[56]
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`3,334,231
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`3,499,152
`3,675,019
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`
`
`References Cited
`
`
`UNITED STATES PATENTS
`
`
`
`8/1967
`Bernstein .......................... .. 250/355
`
`
`
`3/1970 Hetenhouser . . . . . .
`. . . . .. 250/354 X
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`
`
`Hill et al. ...................... .. 250/355 X
`7/1972
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`
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`Primary Examiner—Archie R. Borchelt
`
`
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`Attorney, Agent, or Firm—Stanley Z. Cole; Leon F.
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`
`
`Herbert; Edward J. Radlo
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`
`
`
`[57]
`
`ABSTRACT
`
`
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`A system and method for metering the quantity of ra-
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`diation administered a subject by a source of radiation
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`movable along a path relative to the subject. The sys-
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`tem cumulatively counts the amount of radiation di-
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`rected toward the subject during each of a succession
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`of increments of motion of the source. When a prede-
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`termined amount of radiation is delivered during an
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`increment,
`the source is disabled until
`the source
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`passes into the next increment of displacement. The
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`count of radiation is restarted at the instant the source
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`is disabled, to accumulate accurately any added spuri-
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`ous radiation dosage which may occur and to include
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`that dosage in the count of the permitted amount for
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`the next succeeding increment of motion. Several in-
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`terlocks for disabling the system in response to various
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`malfunctions are included. Means for controlling the
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`speed of movement of the source and/or the dose rate
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`of the source are also included.
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`33 Claims, 4 Drawing Figures
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`60
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`COUNTER -COMPARATOR
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`Page 1 of 14
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`Elekta Exhibit 1034
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`Page 1 of 14
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`Elekta Exhibit 1034
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`

`
`a"AIEN1tUSEP!639?5
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`3,905,233
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`Page 2 of 14
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`Page 2 of 14
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`;3ATENTE[] SEP 1 61975
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`2|
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`FIG. 2
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`VARIABLE
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`Page 3 of 14
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`Page 4 of 14
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`Page 4 of 14
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`PATENTEDSEP : 5 1975
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`3, gQ5,233
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`Page 5 of 14
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`

`
`1
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`SYSTEM AND METHOD FOR ADMINISTERING
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`
`
`RADIATION
`
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`3,906,233
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`2
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`l0
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`20
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`25
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`30
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`35
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`BACKGROUND OF THE INVENTION"
`.
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`1. Field of the Invention
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`This invention relates to the field of apparatus and
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`method for controlledly irradiating a subject. More
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`particularly, the invention pertains to administering a
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`predetermined maximum dose of radiation during each
`of several increments of relative motion of the radia-
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`tion source relative to the subject.
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`,
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`2. Description of Prior Art
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`It is known to irradiate a subject by relatively moving
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`a source of radiation about the subject along a path. A
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`15
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`benefit of this method of delivering radiation is that the
`radiation may be focused upon a “target” area which
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`will be constantly irradiated during the movement of
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`the source. The surroundingareas, however, receive
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`only a portion of the radiation dosage which is deliv-
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`ered to the target. This technique has utility in thera-
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`peutic applications where it is generally desirable to
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`apply a high dosage of radiation to a target organ or
`part of the body, and where it is desirable as well to re-
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`strict as much as possible the radiation delivered to sur-
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`rounding tissues.
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`The normal way ofadministering radiation according
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`to the above limitations is to position the patient or sub-
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`ject on a stationary object, while moving the radiation
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`source along a circular path surrounding the target re-
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`gion. The source of radiation is preset to emit the radia-
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`tion at a known rate. The length of the path or are tra-
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`versed by the source is predetermined, as is the velocity
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`with which the source moves. These variables together
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`determine the dosage ultimately administered to the
`target area.
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`Several difficulties, however, are commonly experi-
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`enced in the execution of this technique. First, it is
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`often difficult to govern with the desired accuracy‘ the
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`velocity of the source. Radiation sources are commonly
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`40
`very massive components, and apparatus to govern
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`their motion generally involves the use of counter-
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`weights, which counterweights may not be perfectly
`balanced, thus imparting variations in speed of the en-
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`tire combination. Other factors, such as bearing mal-
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`function may also exert anundesirable influence.
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`Moreover, it is not always possible to regulate the
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`rate at which the source emits radiation with the de- .
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`sired precision. Such factors as line voltage variations,
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`which are difficult to detect and eliminate, can substan-
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`tially affect the output of the source.
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`It sometimes occurs in the operation of such radia- ~
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`tion systems that spurious radiation may be emitted by
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`the source. The dangers and complications of such
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`emissions are clear.
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`Furthermore, certain other basic malfunctions of the
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`system may arise which render its operation ineffective
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`or deleterious. For example, the velocity of the source
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`may be so low as to severely overexpose a portion of
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`60
`the target area to radiation. Also,‘ the output of -the
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`source may for any of a -number of reasonsdrop -below‘ .
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`an effective value, notwithstanding that the sourcemay;
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`remain operable to some degree.
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`Consequently, it is a major object of this invention to
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`provide a method and system< for controlling -‘the
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`amount of radiation incident onto a target, while com-
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`pensating for the unwanted ‘variations and irregularities
`noted above.
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`It
`is another object of the invention to provide a
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`method and system having sufficient flexibility to com-
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`pensate for variations in radiation which tend to result
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`from imprecise control of source velocity and of inten-
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`sity of radiation from the source.
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`It is a further object to provide a system and method
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`in which the path of motion of the source is divided into
`a plurality of increments, and the radiation emanating
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`from the source is regulated to a predetermined maxi-
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`mum value during the traversal by the source of each
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`of the increments of motion.
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`It is a further object of this invention to provide a sys-
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`tem and method according to the above description in
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`which the existence of any spurious radiation from the
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`source is taken into account in establishing the afore-
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`mentioned maximum dosage for each increment of mo-
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`tion.
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`It is an additional object of this invention to provide
`
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`a method and system whereby, notwithstanding the po-
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`tential irregularity of radiation resulting from the nonu-
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`niformity of source velocity and radiation output, the
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`radiation is administered to the subject in a substan-
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`tially uniform fashion throughout the movement of the
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`‘source along its predetermined path.
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`It is another object to provide a system and apparatus
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`for providing an indication when the dosage delivered
`during any increment of motion of the source falls
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`below a predetermined level.
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`It is still another object to provide a system and appa-
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`ratus for producing an indication when the speed at
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`which the source traverses any increment of motion
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`falls below a predetermined value.
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`It is a further object to provide a system and appara-
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`
`
`tus for providing an indication if the dosages delivered
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`
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`
`
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`during any increment of motion is significantly greater
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`
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`
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`then the desired dosage.
`
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`It is a another object to provide a system and appara-
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`
`
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`
`
`
`tus for providing an indication of an unacceptable
`
`
`
`
`
`
`
`
`amount of radiation during the time the source is in-
`
`
`
`
`
`
`
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`tended to be inactivated.
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`
`It is an additional object to provide a system and ap-
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`
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`
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`paratus which includes flexibility in selecting different
`speeds of movement of the source and/or different dose
`
`
`
`
`
`
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`rates of the source.
`
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`SUMMARY OF THE INVENTION
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`This invention relates to a system for metering the
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`amount of radiation which is delivered to a target area
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`of a subject by means of a radiation source which is
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`movable along a particular path with respect to the sub-
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`ject. ln the preferred embodiment of this invention, the
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`path of motion of the radiation source is along a circu-
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`lar or arcuate course. The system incorporates drive
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`means for propelling the source along its path at a con-
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`trollable speed. Also included is a sensor for generating
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`a signal indicative of the position of the source along
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`the path. Additionally, the apparatus included within
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`the system comprises a counter which emits a signal
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`whenever the position of the source changes by a pre-
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`determined amount, this amount being 2° in one pre-
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`ferred embodiment.
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`The radiation source is provided with an ionization
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`chamber in the path of emitted radiation, along with
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`‘ associated circuitry to render the chamber an accurate
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`sensor’ of the amount of radiation passing from the
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`source toward the subject. The circuitry generates a
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`signal corresponding to the amount of sensed radiation.
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`Page 6 of 14
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`A counter cumulatively records the sensed radiation.
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`Means is provided for independently presetting a signal
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`corresponding to a particular given maximum radiation
`which is desired to be permitted during the traversal by
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`the source of any one increment of motion.
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`This signal, and the signal representing the amount of
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`radiation sensed by the ionization chamber,‘ are
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`brought together in a comparator. The comparator is
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`designed to emit a stop signal whenever the total
`amount of radiation accumulating during any given in-
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`crement equals or exceeds the value of the quantity of
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`radiation which is independently presented as indicated
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`above. The stop signal V turns off the‘ source. The
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`counter of radiation, which is connected to the radia-
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`tion sensor, is reset by the occurrence of the stop sig-
`nal. Thus, the counter reinitiates the count every time
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`the source completes the generation of its predeter-
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`mined maximum_ radiation for one_ increment.
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`The disablement of the source continues until it has
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`completed’ its traversal through that particular incre-
`ment of motion for which the radiation had been
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`counted, and during which the predetermined amount
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`of radiation had been delivered.
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`The inherent consequence of this configuration of
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`apparatus and circuitry is, that, for any given increment
`of motion, there is established a predetermined maxi-
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`mum value of radiation which substantially cannot be
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`exceeded during any of the increments of motion.
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`When the source begins to traverse a subsequent in-
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`crement of motion, it is reactuated to begin delivering
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`radiation toward the subject once more.
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`Note that, as mentioned above, the counter itself is
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`reset to zero upon the issuance of the stop signal from
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`the comparator which effects the disablement of the
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`source when the radiation for the particular increment
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`being traversed equals or exceeds the predetermined
`' value which is preset. The reason for thisis to enable
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`the counter to correctly record the incidence of any
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`spurious or accidental radiation which may be emitted
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`by the source. The occurrence of any such radiation is
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`thus taken into account in governing the amount of ra-
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`diation administered in the succeeding increment of
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`motion. Thus, this system possesses the flexibility of
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`compensating for inaccuracies in the control of the
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`source itself.
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`The system, as can be seen, measures the amount of
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`radiation delivered to the subject during each and
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`every increment of motion and limits that amount to a
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`prespecified maximum. The total amount of radiation
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`delivered can thus be limited very precisely. Addition-
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`ally, the system maintains uniformity in the delivery of
`radiation from various directions as the source moves
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`along its path of motion.
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`Several interlocks are built into the system of this in-
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`vention in order to provide an indication when a basic
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`malfunction occurs, and to, where warranted, disable
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`the radiation delivery apparatus. For example, a special
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`counter is provided which is actuated only during those
`periods in which the radiation source has been theoreti-
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`cally disabled by the stop signal from the comparator.
`This counter is programmed such that it emits a signal
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`when a predetermined amount of radiation escapes
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`from the radiation source during a time when it is sup-
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`posedly turned off. If such a condition occurs, a fault
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`signal is generated, which disables the entire system by
`cutting off the power supply.
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`4
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`A second interlock senses the time required for the
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`source to traverse a particular increment of motion. If
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`the time required for such traversal is excessive, a simi-
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`lar fault signal is generated.
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`Two other types of interlocks generate a fault signal
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`if it appears that the radiation administered during an
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`increment is less or morethan the desired amount.
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`Note that, in the utilization of this system, the output
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`dose rate of the radiation source is normally at a rate
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`which, if the source were allowed to traverse its entire
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`course or path in the activated state, would result in an
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`overdose of radiation. Since the system of this inven-
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`tion has the flexibility of interrupting the dosage of ra-
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`diation whenever the dosage given in any one incre-
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`ment is sufficient, it is possible to assure in this way that
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`the dosage given over the entire path will cumulatively
`be sufficient’. At the same time the system permits se-
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`lection of traversal speed and/or dose rate of the source
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`so that the desired dose per increment can be adminis-
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`tered over almost the entire path of each increment.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG. 1 is a‘ block schematic diagram illustrating the
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`components of the system of this invention;
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`FIG. 2 is a portion of the schematic diagram illustrat-
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`ing in greater detail the components of the system of
`this invention;
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`FIG. 3 is another portion of the schematic diagram
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`showing in detailed fashion the elements of the inven-
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`tion; and
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`FIG. 4 is a block diagram disclosing a further em-
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`bodiment of the invention.
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`DESCRIPTION _OF THE PREFERRED
`EMBODIMENT
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`FIG. 1 enables a concise understanding of the system
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`of this invention. A conventional radiation source 5 is
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`mounted on the arm of a U-shaped member 6 and de-
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`livers X-rays along an axis 7 toward a subject or patient
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`8 positioned on a couch 9. The U-shaped support in-
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`cluding source 5 is mounted on a housing 10 for rota-
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`tion about an axis 11. Drive means such as a variable
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`speed motor 12 and gears 13 and 14 drive the source
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`for rotation about axis 11. The X-ray beam emerging
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`from the source passes through a convention ionization
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`chamber or radiation sensor 15. Integrator 20 emits a
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`digital signal which is proportional to the quantity of
`radiation delivered by the source 5. Integrator 20 re-
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`ceives its input from the ionization chamber (radiation
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`sensor) 15 located in the path of radiation from the
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`source 5. The ionization chamber. 15 contains a gas
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`such as air which ionizes in the presence of radiation
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`incident thereon such that electrodes positioned in the
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`chamber and connected together through a load de-
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`velop a current flowing between them which is a func-
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`tion of the radiation incident upon the chamber. The
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`current from said electrodes is delivered to integrator
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`20. The particular structure of integrator 20 and ioniza-
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`tion chamber 15 does not constitute a part of this in-
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`vention, and hence is not described in greater detail.
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`The signal from integrator‘ 20 passes to divider 30.
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`Integrator 20 emits a signal which indicates units of
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`decirads in a preferred embodiment. As will be ex-
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`plainedhereinbelow, the motion of the source will be
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`calibrated in two degree increments in a preferred em-
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`bodiment. Therefore, in order toderive a signal from
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`divider 30 which is indicative of the radiation delivered
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`Page 7 of 14
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`per degree of arc, divider 30 produces an output signal
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`at one output which is divided by two. Obviously, if mo-
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`tion of the source 5 is calibrated in one degree incre-
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`ments, the output signal would not be divided by two.
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`The signal which is divided by two is input to counter
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`40, which will be described below.
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`A second output of divider 30 produces a signal
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`which is divided by a factor of 10, and presented as an
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`input to a display apparatus associated with the main
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`console (not shown) within view of the operator of the
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`system, in order to present an instantaneous viewing of
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`the quantity of radiation having been administered in
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`rads.
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`The signal corresponding to the amount of radiation
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`accumulated (divided by two) is input to counter 40.
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`Counter 40 stores this integrated amount of radiation
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`as it accumulates.
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`Presetting switch 50 is adapted to generate a radia-
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`tion limit signal which is a function of a quantity of ra-
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`diation which may be manually preset into presetting
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`switch 50. The format of the radiation limit signal
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`thereby generated corresponds to the format in which
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`the accumulated radiation signal is stored in counter
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`40; that is, decirads desired per one degree increment.
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`The accumulated radiation signal and the radiation
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`limit signal are each directed as inputs to comparator
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`60. Comparator 60 produces an output signal when-
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`ever the stored radiation signal in counter 40 equals or
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`exceeds the radiation limit signal input from presetting
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`switch 50.
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`This stop signal is input to switch 70. Switch 70 is
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`connected to the radiation source in such a way that it
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`is responsive to the occurrence of the stop signal from
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`comparator 60 to disable the source to prevent it from
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`emitting any further radiation.
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`The radiation source 5, together with the other appa-
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`ratus, such as counterweights, which are movable
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`therewith, form the U-shaped member 6 and are com-
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`monly known as the gantry of the radiation system. For
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`example, see U.S. Pat. No. 3,720,817. The U-shaped
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`member of gantry 6 is provided with position sensor 80,
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`which is connected thereto, and which produces a sig-
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`nal which is a function of the rotational position of the
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`gantry. This position signal is directed as an input to
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`traversal sensor 90. Traversal sensor 90 produces an
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`output pulse whenever the gantry rotates through a two
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`degree increment. The signal output from traversal sen-
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`sor 90 represents an enabling signal directed to switch
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`70. The occurrence of this enabling signal resets switch
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`70 such that the radiation source is re-enabled to begin
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`once more to emit radiation.
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`Comparator 60 is connected to counter 40 such that
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`the occurrence of the stop signal produced by the com-
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`parator, in addition to disabling the radiation source,
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`also resets counter 40 to zero to begin cumulatively
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`counting the radiation which is delivered by the source
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`toward the subject.
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`It is thus evident that this system limits the amount of
`60
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`radiation delivered by the source toward the subject
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`during each two degree increment of rotation of the
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`gantry to that quantity of radiation which is preset into
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`presetting switch 50. When that quantity is reached
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`during any two degree increment, comparator 60 actu-
`ates switch 70 to turn off the radiation source. The ra-
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`diation source remains in the off state until it is turned
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`on again by the passage of the gantry into a subsequent
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`Page 8 of 14
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`3,906,233
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`two degree increment of rotation, at which point the
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`source is reactuated.
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`As noted above, the occurrence of the stop signal
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`from comparator 60 resets counter 40. This can occur
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`before the end of the traversal of the gantry over a par-
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`ticular two degree increment. Thus, counter 40 can cu-
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`mulatively count radiation which may occur after the
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`radiation source is supposedly turned to the off state by
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`the stop signal. The reason for this is that integrator 20
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`does not produce a signal corresponding to the amount
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`of radiation instantaneously with the occurrence of that
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`radiation. Thus, even though the source may be turned
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`off, there will be registered at the output of integrator
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`20 additional radiation shortly after the instant at
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`which the source is turned off. It is clearly desirable to
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`incorporate this delayed count of additional radiation
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`in order to precisely control the quantity of radiation
`incident on the subject.
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`Several interlocks are provided in the system of this
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`invention for indicating various types of malfunctions
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`of the system or of the associated apparatus.
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`The first of these interlocks comprises an additional
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`counting means 100. Counter 100 receives the same
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`input of accumulated radiation which is delivered to
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`counter 40. Alternatively, as a double check, counter
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`100 can be fed with a divided signal from an indepen-
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`dent integrator which receives its input from additional
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`electrode means in the ionization chamber. In either
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`case, counter 100 is actuated to record its count only
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`when the radiation source is programmed by the stop
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`signal to be in its off state. Counter 100 senses that the
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`radiation source is in its off state by means of switch
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`20, switch 120 being responsive to the stop signal to
`emit an off signal which is input to counter 100 to en-
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`able it to count. Counter 100 is reset to zero when tra-
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`versal sensor 90 signals that two degrees of rotation
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`have been completed, at which time the source is reac-
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`tivated.
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`Counter 100 is programmed to emit a fault signal if,
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`during the off state of the radiation source, a predeter-
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`mined amount of radiation is detected and counted at
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`counter 100. This fault signal is delivered as an input
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`to OR gate 110. OR gate 110, in response to the input
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`of a fault signal from counter 100, produces an output
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`signal which is directed to a supplemental disabling
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`means for the radiation source. In this preferred em-
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`bodiment,
`that supplemental disabling means com-
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`prises a means responsive to an output from OR gate
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`110 to cut off the entire high power supply from the en-
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`tire system, and thus deactivate the radiation source
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`and the gantry drive motor. Low voltage to controls
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`and monitoring devices remains on. When the high
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`voltage system thus shuts down, the subject is protected
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`from additional radiation, and the operator is free to
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`correct the difficulty and restart the system.
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`A second fault interlock comprises timer 130. Timer
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`130 is connected to receive the pulses generated by tra-
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`versal sensor 90 whenever the gantry moves through
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`one two-degree increment of rotation. Timer 130 is
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`programmed to emit an output fault signal to OR gate
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`1 10 whenever the gantry fails to traverse one of the two
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`degree increments within a predetermined amount of
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`time. In this preferred embodiment, the maximum time
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`permitted for traversal of a two degree increment is
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`0.08 minutes. If the gantry fails to make that traversal
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`in the prespecified time period, the output signal from
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`Page 8 of 14
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`8
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`the rotation of the gantry when the preset position limit
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`is reached, or to the high voltage supply.
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`FIGS. 2 and 3 illustrate in schematic form the princi-
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`pal components of the system of this invention. FIGS.
`2 and 3 are interconnected as indicated by the lettered
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`lines at the right of FIG. 2 and the left of FIG. 3. More
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`specifically line A of FIG. 2 is connected to line A of
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`FIG. 3, line B is connected to line B, etc. It is noted that
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`many of the components of this specific preferred em-
`bodiment are made up, in whole or in part, by inte-
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`grated circuit elements as shown in FIGS. 2 and 3 as
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`bearing its particular identifying integrated circuit
`number. These numbers are standardized among those
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`of skill in the art dealing with such integrated circuit
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`components. The drawings do not show more than a
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`schematic rendition of the radiation source and related
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`mechanism for driving the source around a patient
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`couch since these are well known in the art, as shown
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`for example in U.S. Pat. Nos. 3,582,650 and 3,720,817.
`Although the invention is described for use in treat-
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`ment of a patient with X-ray radiation, it is useful

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