Radiation teletherapy imaging system having plural ionization chambers

Apparatus for imaging a high energy beam of radiation emanated from a radiation source and transmitted through an object comprising:

• detector means for quantitatively measuring and detecting said transmitted radiation, said detector means comprising a plurality of ion chambers, each of said ion chambers having a longitudinal extent, said ion chambers being disposed in a parallel, side-by-side manner whereby said detector means comprises an array of said ion chambers;
• said plurality of ion chambers comprising at least a first front surface electrode and a plurality of substantially parallel, longitudinally extending collecting electrodes disposed to be facing said front surface electrode and spaced apart at a predetermined distance, wherein said plurality of ion chambers has a predetermined total width at least as great as a maximum width dimension of a target area to be imaged, and wherein said longitudinal extent of said plurality of ion chambers has a predetermined length at least as great as a maximum length dimension of said target area,
• said detector means being disposed on a side of said object opposite that of said radiation source;
• means for converting an ionization current measured by each of said ion chambers into projection data representative of an amount of radiation adsorbed by each of said ion chambers;
• means for converting said projection data obtained from each of said ion chambers into a single projection containing data measured from each of said ion chambers;
• means for displaying said single projection;
• wherein an ionizing medium disposed between said front surface electrode and said collecting electrodes comprises a liquid;
• and
• wherein said liquid ionizing medium comprises a non-flammable liquid fluorocarbon.

Apparatus for imaging a high energy beam of radiation emanated from a radiation source and transmitted through an object comprising:

• detector means for quantitatively measuring and detecting said transmitted radiation, said detector means comprising a plurality of ion chambers, each of said ion chambers having a longitudinal extent, said ion chambers being disposed in a parallel, side-by-side manner whereby said detector means comprises an array of said ion chambers;
• said plurality of ion chambers comprising at least a first front surface electrode and a plurality of substantially parallel, longitudinally extending collecting electrodes disposed to be facing said front surface electrode and spaced apart at a predetermined distance, wherein said plurality of ion chambers has a predetermined total width at least as great as a maximum width dimension of a target area to be imaged, and wherein said longitudinal extent of said plurality of ion chambers has a predetermined length at least as great as a maximum length dimension of said target area,
• said detector means being disposed on a side of said object opposite that of said radiation source;
• means for converting an ionization current measured by each of said ion chambers into projection data representative of an amount of radiation adsorbed by each of said ion chambers;
• means for converting said projection data obtained from each of said ion chambers into a single projection containing data measured from each of said ion chambers;
• means for displaying said single projection;
• wherein a first backing member and said front surface electrode disposed thereon comprise a first circuit board, and wherein a second backing member and said collecting electrodes disposed thereon comprises a second circuit board, said first and second circuit boards having a non-conductive backing layer and facing surface of conductive material, said second circuit board having a plurality of substantially parallel, longitudinally extending strips of a conductive material spaced apart at a predetermined distance;
• and
• said apparatus further comprising means for increasing a ratio of primary electrons to scattered radiation to be detected by an ionizing medium of said detector means, said ratio increasing means being disposed adjacent to said first backing member on a side of said backing member opposite said front surface electrode, said ratio increasing means having length and width dimensions substantially equal to those of said first backing member, said ratio increasing means further having a predetermined thickness sufficient to adsorb at least a portion of the scattered radiation generated by said high energy beam of radiation when said beam is transmitted through said object.

Apparatus for imaging a high energy beam of radiation emanated from a radiation source and transmitted through an object comprising:

• detector means for quantitatively measuring and detecting said transmitted radiation, said detector means comprising a plurality of ion chambers, each of said ion chambers having a longitudinal extent, said ion chambers being disposed in a parallel, side-by-side manner whereby said detector means comprises an array of said ion chambers;
• said plurality of ion chambers comprising at least a first front surface electrode and a plurality of substantially parallel, longitudinally extending collecting electrodes disposed to be facing said front surface electrode and spaced apart at a predetermined distance, wherein said plurality of ion chambers has a predetermined total width at least as great as a maximum width dimension of a target area to be imaged, and wherein said longitudinal extent of said plurality of ion chambers has a predetermined length at least as great as a maximum length dimension of said target area,
• said detector means being disposed on a side of said object opposite that of said radiation source;
• means for converting an ionization current measured by each of said ion chambers into projection data representative of an amount of radiation adsorbed by each of said ion chambers;
• means for converting said projection data obtained from each of said ion chambers into a single projection containing data measured from each of said ion chambers;
• means for displaying said single projection;
• and
• said apparatus further comprises means for rotating said detector means.

Apparatus for imaging a high energy teletherapy beam of radiation transmitted through an object comprising:

• a detector having a first plurality of front surface electrodes, each of said electrodes having a longitudinal extent, a second plurality of collecting electrodes, each of said collecting electrodes having a longitudinal extent, wherein each of said front surface electrodes has a collecting electrode associated therewith, each pair of associated front surface and collecting electrodes extending in a parallel, spaced apart manner, the pairs of associated electrodes thereby forming a plurality of ion chambers adapted to measure a quantity of radiation absorbed by an ionizing medium disposed between each pair of associated front surface and collecting electrodes;
• means for converting said measurement of said radiation absorbed by each of said plurality of ion chambers of said detector into digital projection data representative of an amount of radiation absorbed by each of said plurality of ion chambers;
• means for rotating said detector about a vertical axis with respect to said teletherpy beam and said object;
• means for controlling said rotating means to rotate said detector through a predetermined sequence of orientations;
• means for converting projection data obtained at each orientation of said detector into a single projection containing data from all of said orientations;
• and
• means for displaying said projection data.

Apparatus for measuring and displaying an image of high energy, megavoltage radiation transmitted from a radiation source through an object, such as a patient undergoing radiation therapy, comprising:

• a detector comprising a plurality of ion chambers, each of said ion chambers having a longitudinal extent, each of said ion chambers further having a front surface electrode and a collecting electrode, and having an ionizing medium disposed between said electrodes, each of said plurality of ion chambers being disposed immediately adjacent to at least one other of said plurality of ion chambers, said plurality of ion chambers forming a detector array disposed perpendicularly to a centerline of a radiation beam emanating from said radiation source;
• a motor adapted to rotate said detector with respect to said object;
• means for controlling said motor, whereby said detector may be moved through a predetermined sequence of orientations for obtaining ionization current measurements from each of said ion chambers at each orientation of said sequence;
• measuring means for integrating said ionization current produced in each of said ion chambers at each orientation;
• means for converting said ionization current measurements into digital form;
• means for performing a convolution filtering of said measurements in digital form;
• means for back-projecting all of said measurements into a single projection;
• and
• means for displaying said single projection.

A method for imaging a radiation portal of a high energy radiation therapy machine comprising the steps of:

• (a) positioning a detector comprising a parallel array of ion chambers on a side of an object being treated opposite a radiation source;
• (b) further positioning said detector at an initial measurement position;
• (c) measuring an ionization current generated by each of said ion chambers for a predetermined time period, said ionization current being representative of the radiation absorbed by an ionizing medium in each of said ion chambers at said initial measurement position;
• (d) converting each of said measured ionization current into digital data;
• (e) individually filtering said converted data from each ion chamber of said detector;
• (f) back-projecting said data from all of said ion chambers of said detector;
• (g) moving said detector to a subsequent predetermined position by rotation about an axis formed by said radiation source and said object;
• (h) measuring an ionization current generated in each ion chamber in said array of ion chambers at said subsequent position for said predetermined time period;
• (i) further moving said detector through a predetermined series of orientations by rotation about said axis formed by said radiation source and said object;
• (j) measuring ionization currents generated by each of said ion chambers at each of said orientations for said predetermined time period;
• (k) converting each of said measured ionization current into digital data;
• (l) individually filtering said converted data from each ion chamber of said detector;
• (m) back-projecting said data from all of said positions of said detector;
• and
• (n) displaying said back-projection data on a video monitor.

A method for imaging high energy radiation emanated from a radiation source and transmitted through an object comprising:

• (a) positioning a detector comprising a plurality of parallel ion chambers on a side of said object opposite said radiation source in a predetermined initial position;
• (b) measuring an amount of radiation transmitted from said radiation source through said object to said detector for a predetermined time period;
• (c) rotating said detector through a predetermined sequence of orientations about an axis formed by said radiation source and said object;
• (d) measuring an amount of radiation transmitted from said radiation source to each of said plurality of ion chambers of said detector at each orientation for said predetermined time period;
• (e) converting each of said measurements to digital data;
• (f) reconstructing an image of an irradiated area from said data and
• (g) displaying the image thus obtained.