X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
1999-05-27
2002-05-21
Bruce, David V. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S151000
Reexamination Certificate
active
06393096
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and apparatus for conformal radiation therapy of tumors with a radiation beam having a pre-determined, constant beam intensity.
2. Description of the Prior Art
Modem day radiation therapy of tumors has two goals: eradication of the tumor and avoidance of damage to healthy tissue and organs present near the tumor. It is known that a vast majority of tumors can be eradicated completely if a sufficient radiation dose is delivered to the tumor volume; however, complications may result from use of the necessary effective radiation dose, due to damage to healthy tissue which surrounds the tumor, or to other healthy body organs located close to the tumor. The goal of conformal radiation therapy is to confine the delivered radiation dose to only the tumor volume defined by the outer surfaces of the tumor, while minimizing the dose of radiation to surrounding healthy tissue or adjacent healthy organs.
Conformal radiation therapy has been traditionally approached through a range of techniques, and typically uses a linear accelerator (“LINAC”) as the source of the radiation beam used to treat the tumor. The linear accelerator typically has a radiation beam source which is rotated about the patient and directs the radiation beam toward the tumor to be treated. The beam intensity of the radiation beam is a predetermined, constant beam intensity. Multileaf collimators, which have multiple leaf, or finger, projections which can be moved individually into and out of the path of the radiation beam, can be programmed to follow the spatial contour of the tumor as seen by the radiation beam as it passes through the tumor, or the “beam's eye view” of the tumor during the rotation of the radiation beam source, which is mounted on a rotatable gantry of the linear accelerator. The multiple leaves of the multileaf collimator form an outline of the tumor shape as presented by the tumor volume in the direction of the path of travel of the radiation beam, and thus block the transmission of radiation to tissue disposed outside the tumor's spatial outline as presented to the radiation beam, dependent upon the beam's particular radial orientation with respect to the tumor volume.
Another approach to conformal radiation therapy involves the use of independently controlled collimator jaws which can scan a slit field across a stationary patient at the same time that a separate set of collimator jaws follows the target volume as the gantry of the linear accelerator rotates. An additional approach has been the use of attachments for LINACs which allow a slit to be scanned across the patient, the intensity of the radiation beam in the entire slit being modified as the slit is being scanned.
A further approach for conformal radiation therapy treatment has been the use of a narrow pencil beam of high energy photons, whose energy can be varied, and the beam is scanned over the tumor target volume so as to deliver the best possible radiation dose distribution in each orientation of the gantry upon which the photon beam source is mounted.
A major problem associated with such prior art methods of conformal radiation therapy are that if the tumor volume has concave borders, or surfaces, varying the spatial configuration, or contour, of the radiation beam, is only successful part of the time. In particular, when the convolutions, or outer surfaces, of a tumor are re-entrant, or concave, in a plane parallel to the path of the radiation treatment beam, healthy tissue or organs may be disposed within the concavities formed by the outer tumor concave surfaces, as well as the fact that the thickness of the tumor varies along the path of the radiation beam.
In order to be able to treat tumors having concave borders, it is necessary to vary the intensity of the radiation beam across the surface of the tumor, as well as vary the outer configuration of the beam to conform to the shape of the tumor presented to the radiation beam. The beam intensity of each radiation beam segment should be able to be modulated to have a beam intensity related to the thickness of the portion of the tumor through which the radiation beam passes. For example, where the radiation beam is to pass through a thick section of a tumor, the beam intensity should be higher than when the radiation beam passes through a thin section of the tumor.
Dedicated scanning beam therapy machines have been developed wherein beam intensity modulation can be accomplished through the use of a scanning pencil beam of high energy photons. The beam intensity of this device is modulated by increasing the power of its electron gun generating the beam. The power increase is directed under computer control, as the gun is steered around the tumor by moving the gantry upon which it is mounted and the table upon which the patient lies. The effect is one of progressively “painting” the target with the thickness, or intensity, of the paint, or radiation beam intensity, being varied by the amount of paint on the brush, or how much power is applied to the electron gun, as the electron gun moves over the tumor. Such dedicated scanning beam therapy machines, which utilize direct beam energy modulation, are expensive and quite time consuming in their use and operation, and are believed to have associated with them a significant patient liability due to concerns over the computer control of the treatment beam itself.
Other methods and apparatus for conformal radiation therapy have been developed that spatially modulate the beam intensity of a radiation beam across a volume of tissue in accordance with the thickness of the tumor in the volume of tissue by utilizing a plurality of radiation beam segments. Such methods and apparatus utilize attenuating leaves, or shutters, in a rack positioned within the radiation beam before the beam enters the patient. The tumor is exposed to radiation in slices, each slice being selectively segmented by the shutters. However, a minor disadvantage of that method and apparatus results from the fact that only two slices of tissue volume may be treated with one rotation of the gantry of the linear accelerator. Although the slices may be of arbitrary thickness, greater resolution is accomplished by selecting slices for treatment that are as thin as possible. As the thickness of the treatment slices decreases, the time it takes to treat the patient increases because more treatment slices are required in order to treat the entire tumor volume.
A new method and apparatus for conformal radiation therapy, for use with a radiation beam having a predetermined, constant beam intensity for treatment of a tumor has been proposed in co-pending patent application Ser. No. 08/634,785 to Mark P. Carol, filed Apr. 19, 1996, which includes a radiation beam source for producing a radiation beam having a predetermined, constant beam intensity; at least a 3×3 checkerboard array having alternating radiolucent and radiopaque compartments, for separating the radiation treatment beam into an array of a plurality of beam segments; and means for independently modulating the beam intensity of the radiation beam segments to spatially modulate the beam intensity of the radiation treatment beam across the tumor.
The foregoing methods and apparatus are designed to minimize the portion of the structures being exposed to radiation. However, because exposure to surrounding structures cannot be completely prevented, treatment plans are desired that are optimized to eradicate the tumor volume while minimizing the amounts of radiation delivered to the surrounding structures. Existing methods and apparatus for optimizing treatment plans use a computer to rate possible plans based on score functions which simulate a physician's assessment of a treatment plan. However, existing methods and apparatus have proven to be insufficient.
Existing methods and apparatus utilize a computational method of establishing optimized treatment plans based on an objective cost function that attributes cos
Carol Mark P.
Curran Bruce H.
Hill Robert
Nash Richard
Bracewell & Patterson L.L.P.
Bruce David V.
Nomos Corporation
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