Patent Description:
Several technologies exist for surface dosimetry of subjects undergoing external-beam radiotherapy; dosimetry being used to verify the amount of radiation delivered and placement of ionizing radiation doses delivered during external beam radiation therapy (EBRT). Among the dominant technologies for measurement of surface dose are film, thermo-luminescent dosimeters (TLD), optically-stimulated luminescence dosimeters, silicon diode or MOSFET dosimeters, or scintillator fibers; each of these measurement approaches has issues Inter alia, scintillation imagers suitable for determining beam characteristics are described in <CIT>.

Among these issues is a large burden on staff time in reading out the measurement, especially when TLDs and film are used. Further, application of tethered detectors decreases patient comfort due to the necessity of affixing not only the detectors, but also the readout fibers or wires to the patient's body.

Methods mentioned hereinafter do not form part of the invention. In an embodiment, a system for dosimetry includes a radiation source that provides a pulsed radiation beam to a treatment zone, and a thin sheet of solid scintillator disposed between the radiation source and skin of a subject in the treatment zone. A gated camera images the solid scintillator integrating light from the solid scintillator during multiple pulses of the radiation beam while excluding light received between pulses of the pulsed radiation beam; and an image capture and processing machine that receives images from the gated camera and performs additional corrections to provide a map of dose received by the subject.

The invention may be used in a method for mapping skin dose of a subject during radiation treatment performed with a pulsed radiation beam in a treatment zone The method includes providing a thin sheet of plastic scintillator in contact with skin of a subject; positioning the subject in the treatment zone; and capturing a scintillation image of light received from the plastic scintillator during multiple time windows during pulses of the radiation beam while excluding light received from the plastic scintillator between pulses of the radiation beam. The method also includes capturing a background image of light received during a plurality of time windows, that are non-overlapping the radiation pulse and that have width corresponding to the radiation pulses; and subtracting the background image from the scintillation image.

A radiation treatment system <NUM> (<FIG>) includes a radiation source <NUM> of a beam <NUM> of pulsed, ionizing, radiation of moderate to high energy such as a linear accelerator (LINAC), cyclotron, or other particle accelerator. Beam <NUM> is emitted along a beam axis <NUM> through a collimator <NUM> that may include adjustable shielding shapes configured to determine a shape of beam <NUM>. The beam axis <NUM> and beam <NUM> are aimed towards a treatment zone <NUM> within which a subject <NUM> may be positioned. Shielding <NUM> is positioned at least behind treatment zone <NUM>, and in particular embodiments surrounding the entire system <NUM> to absorb any radiation of beam <NUM> not absorbed by subject <NUM>.

A gated electronic camera, such as an intensified charge-coupled device (ICCD) camera <NUM>, is positioned outside beam <NUM> with a field of view <NUM> aligned along a camera viewing axis <NUM>; camera viewing axis <NUM> is aligned such that field of view <NUM> includes a view of most or all of treatment zone <NUM> including a view of a surface of any subject <NUM> that may be positioned within the treatment zone <NUM>.

In an alternative embodiment, an image-intensified CMOS (ICMOS) camera is substituted for ICCD camera <NUM>; with this camera image capture gating is performed in a manner like that described herein for the ICCD camera. In yet another embodiment, an electronically-gated, sensitive, CMOS (EGCMOS) camera is used in place of ICCD camera <NUM> with image capture timed to coincide with beam pulses as described herein.

For comfort of subject <NUM>, one or more room lighting devices <NUM> are provided that provide room lighting illumination <NUM> to the treatment zone <NUM> and surrounding portions of the room in which the treatment zone <NUM> is located.

Pulse timing signals <NUM> are provided by radiation source <NUM> to an image capture and processing machine <NUM> equipped with a display <NUM> and network connection <NUM> over which images can be viewed and transmitted to external medical records storage systems (not shown).

Pulse timing signals <NUM> are used by image capture and processing machine <NUM> to synchronize time-gated imaging by ICCD camera <NUM> so camera <NUM> captures and images light received by ICCD camera <NUM> during each pulse of radiation source <NUM> while excluding from images light received by ICCD camera <NUM> at times between pulses of radiation source <NUM>. In a particular embodiment, radiation source <NUM> is a LINAC providing a radiation beam <NUM> of high energy electrons in pulses of between three and four microseconds width repeated at a <NUM> Hertz rate, a duty cycle of approximately one in one thousand. In an alternative embodiment, radiation source <NUM> is a pulsed source of a radiation beam <NUM> of high-energy X-ray or gamma-ray photon radiation.

By imaging only during the short pulses of electron radiation emitted by the accelerator, ambient background light is suppressed by a factor of <NUM>, making low-intensity scintillation imaging feasible without need to blank room lighting devices <NUM>.

It is known that some substances, such as europium-doped calcium fluoride or thallium-doped sodium iodide crystals, scintillate (or emit visible light) when they absorb high-energy charged particles or high energy photons. Some radiation detectors, including the detectors in some gamma-ray cameras, operate by localizing flashes of light produced by scintillation in such crystals when radiation is absorbed. For high-energy radiation below a saturation limit, scintillation crystals and materials emit light proportional to both the photon or particle energy and photon or particle quantity of high energy radiation absorbed by them. An issue with classical scintillation crystals is that thick crystals of high-density materials absorb most, if not all, of electron beam radiation striking them and thereby partially or fully shield part or all of any subject positioned behind them. As such, thick scintillation crystals positioned in beam <NUM> between collimator <NUM> and subject <NUM> would block treatment of some or all of subject <NUM>. Such crystals would also absorb a significant percentage of photon-beam radiation such as X or gamma-ray radiation.

A plastic scintillation material, Eljen EL-<NUM>, (Eljen Technology <NUM> W. Broadway, Sweetwater, Texas) has been formed as a one-millimeter thin sheet, thin enough to pass a majority of beam <NUM>, and having low enough density that the one-millimeter thin sheet does not significantly block or absorb radiation of beam <NUM>.

In an embodiment, a one-millimeter thick sheet <NUM> of EL-<NUM> scintillator is positioned as a screen at a radiation-source side of treatment zone <NUM> in a path of beam <NUM> from collimator <NUM> to subject <NUM>, and ICCD camera <NUM> is positioned to image sheet <NUM>.

In an alternative embodiment, a flexible one-millimeter thick sheet <NUM> of EL-<NUM> scintillator is positioned in contact with skin of subject <NUM> in the treatment zone, and ICCD camera <NUM> is positioned to image sheet <NUM>.

In alternative embodiments, thin sheets <NUM> of alternative flexible and stretchable scintillators formed of organic scintillators or powdered inorganic scintillators suspended in a polymer, the polymer may be a transparent plastic or synthetic rubber, are positioned conformal to skin of subject <NUM>; in one alternative embodiment the scintillator is formed as a garment worn by subject <NUM>. For purposes of this document, a thin sheet of scintillator is a transparent, or translucent material that either by itself, or through a second material incorporated within the material, emits pulses of light by any mechanism including scintillation, fluorescence, or Cherenkov, when stimulated by pulses of a charged particle, x-ray or gamma radiation beam, the pulses of light emitted having a wavelength adapted to capture by camera <NUM> and a decay time of less than twice a duration of pulses of the beam, the material being formed as a sheet thin enough to not absorb a significant portion of photons or charged particles of the beam so that at least <NUM>% of energy of a typical radiation treatment beam passes through the material.

In an alternative embodiment, the conformal sheet of scintillator has a black border of width between three and five millimeters, inclusive.

Gated camera <NUM> in an embodiment is an intensified CCD camera, such as a PI-MAX4 1024i (Princeton Instruments, NJ, USA) camera, including an image-intensifier tube and a charge-coupled device semiconductor image sensor. The acceleration voltage of the image-intensifier tube is pulsed synchronous to pulses of the radiation source so that light received from the scintillation material sheets <NUM> or <NUM> is imaged by the gated camera during pulses of the beam <NUM>, while light received between pulses of the beam <NUM> is ignored, to form scintillation images.

With reference to <FIG> and <FIG>, in a method <NUM> of operating the system of <FIG>, in some operations of the system reference dosimeters, which in a particular embodiment are thermos-luminescent dosimeters (TLD dosimeters) and in another particular embodiment are silicon-based diode or MOSFET dosimeters, are positioned <NUM> on subject <NUM> and the thin, approximately one millimeter thick, scintillator sheets <NUM> or <NUM> are positioned <NUM> between radiation source <NUM> with collimator <NUM> and subject <NUM>. The subject is positioned <NUM> in the treatment zone <NUM>.

A background image is captured <NUM> and integrated during the same number of time windows as the scintillation image, the windows are of duration equivalent in width and frequency to the time windows used to capture the scintillation images. The background image windows are timed to not overlap the beam pulse, and in a particular embodiment are delayed from beam pulses. These background image windows are timed late in the beam-pulse to beam-pulse gap to allow decay of any fluorescence in the scintillator sheet.

In an alternative embodiment, the background image is captured <NUM> and integrated during a greater number of wider background capture windows than the windows during which the scintillation images are captured. All background capture windows are non-overlapping pulses of the beam. The total of all the background capture windows provides a total background integration time that is a background multiple of the total integration of each scintillation image, in a particular embodiment being forty times the total integration time of a scintillation image. The background image is then divided by the background multiple to provide an averaged background image. Averaging the background image in this way filters the background image by signal averaging to reduce artifacts and noise in the background image. In these embodiments, the averaged background image is used instead of a raw background image when background is subtracted <NUM> from the scintillation image.

Radiation treatment begins and the CCD or CMOS image sensor integration time of camera <NUM> is configured to integrate light received during one or several time windows during pulses of the beam, and in a particular embodiment <NUM> time windows, each time window synchronized to occur during pulses of the beam, while excluding light received between the time windows from the integration, to capture <NUM> scintillation images.

Images captured by camera <NUM> representing integrated scintillation light from scintillation material sheets <NUM> or <NUM> are received into image capture and processing machine <NUM> where the background image is subtracted <NUM> from the scintillation images to form an intermediate image.

The scintillation images may in some embodiments be filtered by a rank-order filter.

During radiation treatment, intermediate images are integrated <NUM> to form a total dose image.

In one embodiment, the scintillation light output, as imaged in the scintillation images, is related to radiation dose expressed by radiant energy fluence Φs (J m-<NUM>), is proportional to the received dose D = kDΦs, assuming ideal scintillator emission isotropy, the scintillation-dose linearity, and an electronic equilibrium established in the scintillator volume. The dose conversion factor, kD, includes the electron mass collision stopping power of the scintillator, as well as several other factors that contribute to scintillator image formation.

In embodiments, the total dose image is also corrected for scintillator-to-camera distances such as may be measured when the subject is placed in the treatment zone.

In another embodiment, the absolute dose calculation uses a total scintillation photon energy collected by the imaging system: QS = AΩ kcΦs where A is the scintillator area and S2 is the solid angle projected by the imaging system subtended by the scintillator outline in the direction of the camera optical axis. The imaging system sensitivity is contained in constant kc. The scintillator image shows the intensity of scintillation radiant flux QS, measured as a sum of all intensity values within the thresholded image, as well as the scaled radiant energy fluence, ΦS, measured as an average intensity value from an interior region-of-interest. This approach also requires calibration due to the projected solid angle Ω, which depends on scintillator-camera distance d and angle θ of scintillator normal to camera optical axis.

The dose calibration factor kc is acquired at an angle θ = <NUM> and at a specific scintillator camera distance dc.

An additional scintillator-camera distance calibration is carried out to mitigate a small but non-negligible effect of lens throughput at different focal distance values. The lens throughput effect may be approximated to first order by a factor ki (d), yielding a final dose calculation formula.

The absolute dose response calibration of the scintillator imaging system si typically performed by placing the scintillator on a back-scattering water-equivalent phantom along with a group of TLDs or OSLDs. The scintillator-camera distance and angle is measured or calculated from a calibration pattern on the phantom. A scintillation intensity-dose response is then recorded for varying doses delivered to the phantom, and at two or more scintillator-camera distances. We then calculate the dose calibration factor kc at recorded scintillator distance d=dc and observation angle θ, assuming that the angles θ and ρ are small.

The image capture and processing machine <NUM> is configured to then compensate <NUM> each intermediate image and, upon completion of treatment, the total dose image, for inverse square law light loss due to differences in lens distance from scintillation sheets <NUM> or <NUM> and camera <NUM> to form a second intermediate image. This correction <NUM> is particularly useful with conformal sheets <NUM> applied to the subject.

A <NUM>-D imaging camera <NUM> is also positioned to image conformal scintillation material sheets <NUM>, and image capture and processing machine <NUM> is configured to use images from <NUM>-D imaging camera <NUM> to form a three-dimensional model of scintillation material sheets <NUM>. In an embodiment, <NUM>-D imaging is performed in background room lighting. The three-dimensional model is used by image capture and processing machine <NUM> during compensation for inverse square law light loss. In embodiments using the <NUM>-D imaging camera and in which the image capture and processing machine <NUM> forms a three-dimensional model of the scintillation material sheets <NUM>, <NUM> (<FIG>), <NUM> (<FIG>), the conformal scintillation material sheet <NUM>, <NUM> may have optional markings including a black border <NUM>, <NUM> of width three to five millimeters, inclusive, as well as a sheet-identifying identification bar code <NUM>, <NUM>; in these embodiments the markings including the black border <NUM>, <NUM> aids localization of edges of the sheet in three dimensions without significantly impairing dose calculation, and the bar code <NUM>, <NUM> identifies the sheet for calibration purposes. Additional, slender, markings <NUM>, <NUM> may also be present on the sheet to further aid three dimensional modeling of the scintillation material sheet. In embodiments, the scintillation material sheets may be of rectangular <NUM> or round <NUM> shape.

Any other necessary corrections, such as corrections for the increased thickness of scintillator sheet penetrated by beams when sheets are oriented at angles other than perpendicular to the beam, are then made <NUM>.

The intermediate images and total dose images are also compensated <NUM> for scintillator sheet angle relative to the beam axis and camera angles.

Since scintillator sheets may differ in their response to photons or charged particles of beam <NUM>, in an embodiment each scintillator sheet is marked with an identification code, and image capture and processing machine <NUM> has access to a calibration database having calibration information for each sheet indexed by the identification codes of individual scintillator sheets. In a particular embodiment the identification code is a bar code printed on a visible corner of the sheet.

In embodiments using sheets with identification codes, the identification code or codes of sheets in use during a treatment session are entered into image capture and processing machine <NUM>, or image capture and processing machine <NUM> reads the identification code, then accesses <NUM> a calibration record of the database associated with the identified sheet. If a TLD or other reference dosimeter is used during the treatment session, calibration information derived from the reference dosimeter readings are stored in the calibration record of the database associated with the identified sheet. If no reference dosimeter is used during the treatment session, averaged calibration information obtained during prior treatment sessions or during manufacturer calibration is used in calibration compensation for the treatment session.

After treatment or calibration sessions where reference dosimeters such as TLD or OSLD dosimeters are used, the TLD dosimeters are read and used to determine <NUM> a calibration adjustment that allows calculation of an actual dose <NUM> from the peak intensity or integrated intensity of each scintillator image. The calibration adjustment from prior radiation treatment sessions performed with the same scintillator sheet or sheets may in some embodiments also be used to provide real-time, estimated, cumulative dose images during treatment sessions. In treatment sessions where reference dosimeters are omitted, the total dose image is corrected using an average calibration determined from multiple prior sessions using the same or similar scintillator sheets.

In a particular embodiment, in addition to a conformal scintillator sheet <NUM> disposed on or worn by the subject, an additional, calibrated, reference scintillator <NUM> may be positioned in beam <NUM> and in view of camera <NUM>. In this embodiment, light emitted during treatment by reference scintillator <NUM> is used to determine radiation dose available from the beam and used in place of reference dosimeter readings to calibrate individual scintillator sheets and to determine calibration adjustments for the total dose image. The corrected total dose image represents a recording of patient surface dose and is particularly applicable to total skin electron therapy patient dosimetry.

In an alternative embodiment, as illustrated in <FIG>, an intermediate image formed by subtracting <NUM> the background image from the scintillation image is corrected for scintillator sheet and camera angles, lens to sheet distance, and other effects including calibration adjustments before integration <NUM> to form a total dose image.

The features herein disclosed may be combined in multiple ways. Among these are:.

A system for dosimetry designated A, including a radiation source adapted to provide a pulsed radiation beam to a treatment zone; a thin sheet of scintillator disposed between the radiation source and skin of a subject, the thin sheet of scintillator being in the treatment zone; a gated camera configured to image the sheet of scintillator; and an image capture and processing machine coupled to receive images from the gated camera. The gated camera is configured to capture images of light from the thin sheet of scintillator during a plurality of pulses of the pulsed radiation beam while excluding light received from the thin sheet of scintillator between pulses of the plurality of pulses of the pulsed radiation beam to form a scintillation image.

A system designated AA including the system designated A wherein the thin sheet of scintillator is a conformal sheet of a plastic scintillator in contact with skin of the subj ect.

A system designated AB including the system designated A or AA further including a <NUM>-D imaging camera, and wherein the image capture and processing machine is configured to process images from the <NUM>-D imaging camera into a three-dimensional model of the subject and to use the three dimensional model of the subject to correct the scintillation image while determining a corrected total dose image.

A system designated AC including the system designated A, AA, or AB wherein the image capture and processing machine is configured to subtract a background image from the scintillation image, the background image being obtained by the gated camera at times excluding times of pulses of the pulsed radiation beam.

A system designated AD including the system designated A, AA, AB, or AC wherein the image capture and processing machine includes a database containing calibration information associated with individual thin sheets of scintillator, and the image capture and processing machine is configured to correct the scintillation image according to the calibration information.

A method designated B for mapping skin dose of a subject during radiation treatment performed with a pulsed radiation beam in a treatment zone including providing a thin sheet of scintillator in contact with skin of a subject; positioning the subject in the treatment zone; capturing a scintillation image of light received from the thin sheet of scintillator during a plurality of first time windows during pulses of the radiation beam while excluding light received from the thin sheet of scintillator between pulses of the radiation beam; capturing a background image of light received during a plurality of second time windows delayed after the first time windows and having width equal to the width of the first time windows; and subtracting the background image from the scintillation image.

A method designated BA including the method designated B or C wherein the thin sheet of scintillator is a conformal sheet in contact with skin of the subject and further including obtaining <NUM>-D images of the thin sheet of scintillator using a <NUM>-D imaging camera, processing images from the <NUM>-D imaging camera into a three dimensional model of the subject, and using the three dimensional model of the subject to correct the scintillation image while determining a corrected total dose image.

A method designated BB including the method designated B, C, or BA where the thin sheet of scintillator is formed of a plastic adapted to emit light when struck by ionizing radiation.

A method designated BC including the method designated B, C, BA, or BB and further including obtaining calibration data of light emission versus applied radiation dose for the thin sheet of scintillator, and adjusting the scintillation image based on the calibration data.

A method designated BD including the method designated B, C, BA, BB, or BC wherein the radiation beam is an electron beam.

A method designated BE including the method designated B, C, BA, BB, BC, or BD where the thin sheet of scintillator is formed of a plastic adapted to emit light when struck by ionizing radiation.

A method designated BF including the method designated B, C, BA, BB, BC, BD, or BE and including obtaining calibration data of light emission versus applied radiation dose for the thin sheet of scintillator and adjusting the scintillation image based on the calibration data.

A method designated BG including the method designated B, C, BA, BB, BC, BD, BE, or BF, wherein the calibration data is stored in a database, the database indexed by identification information associated with the thin sheet of scintillator.

A method designated C for mapping skin dose of a subject during radiation treatment performed with a pulsed radiation beam in a treatment zone including providing a thin sheet of scintillator in contact with skin of a subject; positioning the subject in the treatment zone; capturing a scintillation image of light received from the thin sheet of scintillator during a plurality of first time windows during pulses of the radiation beam while excluding light received from the thin sheet of scintillator between pulses of the radiation beam; capturing a time-averaged background image of light received during a plurality of second time windows, the second time windows excluding times of pulses of the radiation beam; and subtracting the background image from the scintillation image.

Claim 1:
A system (<NUM>, <NUM>, <NUM>, <NUM>) for dosimetry, comprising:
a radiation source (<NUM>) adapted to provide a pulsed radiation beam (<NUM>, <NUM>) to a treatment zone (<NUM>);
a thin sheet (<NUM>) of scintillator disposed between the radiation source (<NUM>) and skin of a subject (<NUM>), the thin sheet of scintillator being in the treatment zone (<NUM>);
a gated camera (<NUM>, <NUM>) configured to image the sheet (<NUM>) of scintillator; and
an image capture and processing machine (<NUM>) coupled to receive images from the gated camera (<NUM>, <NUM>);
wherein the gated camera (<NUM>, <NUM>) is configured to capture images of light from the thin sheet (<NUM>) of scintillator during a plurality of pulses of the pulsed radiation beam (<NUM>, <NUM>) while excluding light received from the thin sheet (<NUM>) of scintillator between pulses of the plurality of pulses of the pulsed radiation beam (<NUM>, <NUM>) to form a scintillation image, characterised in that the system (<NUM>, <NUM>, <NUM>, <NUM>) further comprises a <NUM>-D imaging camera, and wherein the image capture and
processing machine (<NUM>) is configured to process images from the <NUM>-D imaging camera into a three-dimensional model of the subject (<NUM>) and
to use the three-dimensional model of the subject (<NUM>) to correct the scintillation image while determining a corrected total dose image.