X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
2000-08-17
2004-11-02
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S064000, C378S147000, C378S153000
Reexamination Certificate
active
06813336
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a radiation emitting device, and more particularly, to a method and system for delivering radiation treatment.
BACKGROUND OF THE INVENTION
Radiation emitting devices are generally known and used, for instance, as radiation therapy devices for the treatment of patients. A radiation therapy device generally includes a gantry which can be swiveled around a horizontal axis of rotation in the course of a therapeutic treatment. A linear accelerator is located within the gantry for generating a high energy radiation beam for therapy. This high energy radiation beam may be an electron beam or photon (x-ray) beam, for example. During treatment, the radiation beam is trained on a zone of a patient lying in the isocenter of the gantry rotation.
In order to control the radiation emitted toward the patient, a beam shielding device, such as a plate arrangement or collimator, is typically provided in the trajectory of the radiation beam between the radiation source and the patient. An example of a plate arrangement is a set of four plates which can be used to define an opening for the radiation beam. The collimator is a beam shielding device which may include multiple leaves (e.g., relatively thin plates or rods) typically arranged as opposing leaf pairs. The plates are formed of a relatively dense and radiation impervious material and are generally independently positionable to delimit the radiation beam.
The beam shielding device defines a field on the zone of the patient for which a prescribed amount of radiation is to be delivered. The usual treatment field shape results in a three-dimensional treatment volume which includes segments of normal tissue, thereby limiting the dose that can be given to the tumor. The dose delivered to the tumor can be increased if the amount of normal tissue being irradiated is decreased and the dose delivered to the normal tissue is decreased. Avoidance of delivery of radiation to the healthy organs surrounding and overlying the tumor limits the dosage that can be delivered to the tumor.
The delivery of radiation by a radiation therapy device is typically prescribed by an oncologist. The prescription is a definition of a particular volume and level of radiation permitted to be delivered to that volume. Actual operation of the radiation equipment, however, is normally done by a therapist. The radiation emitting device is programmed to deliver the specific treatment prescribed by the oncologist. When programming the device for treatment, the therapist has to take into account the actual radiation output and has to adjust the dose delivery based on the plate arrangement opening to achieve the prescribed radiation treatment at the desired depth in the target.
The radiation therapist's challenge is to determine the best number of fields and intensity levels to optimize dose volume histograms, which define a cumulative level of radiation that is to be delivered to a specified volume. Typical optimization engines optimize the dose volume histograms by considering the oncologist's prescription, or three-dimensional specification of the dosage to be delivered. In such optimization engines, the three-dimensional volume is broken into cells, each cell defining a particular level of radiation to be administered. The outputs of the optimization engines are intensity maps, which are determined by varying the intensity at each cell in the map. The intensity maps specify a number of fields defining optimized intensity levels at each cell. The fields may be statically or dynamically modulated, such that a different accumulated dosage is received at different points in the field. Once radiation has been delivered according to the intensity map, the accumulated dosage at each cell, or dose volume histogram, should correspond to the prescription as closely as possible.
Conformal arc therapy uses a multi-leaf collimator attached to the gantry to deliver radiation as the gantry moves through an arc. Conformal arc therapy is typically delivered with a wide-leaf (e.g., 1 cm) multi-leaf collimator. In such intensity modulation, borders between critical structures and tumor volumes are sometimes not well approximated with a standard one centimeter width leaf which provides a one centimeter by one centimeter grid (cell size) over the intensity map. Each leaf can be moved longitudinally towards or away from a central axis of the beam, however, the field conformation is limited since the leaves are fixed in all but one linear direction. This results in critical areas adjacent to the border being exposed to radiation and results in sharp transitions along the border. A higher resolution than typically provided with the one centimeter leaf is often required. One possible solution is to provide a collimator with thinner leaves. However, the additional hardware required for the additional leaves is expensive, adds weight to the system, may reduce clearance between the treatment head and the patient, and may decrease reliability and life of the system.
Another method used with conformal arc therapy replaces the multi-leaf collimator with a block formed from a radiation shielding material (e.g., lead alloy) and having an opening shaped to generally correspond to the treatment area. This requires a separate block to be manufactured for each treatment area so that the opening corresponds to the specific shape of the tumor or other area to be radiated.
Accordingly, there is therefore, a need for a method for achieving higher spatial resolution radiation therapy without changing current multi-leaf collimator leaf widths or using lead alloy blocks specially designed for each radiation treatment.
SUMMARY OF THE INVENTION
A method for delivering radiation from a radiation source to a treatment area utilizing a multi-leaf collimator is disclosed. The method includes positioning a multi-leaf collimator between the radiation source and treatment area to block a portion of the radiation and define a first treatment field. The collimator is positioned with the leaves of the collimator extending longitudinally in a first direction. The method further includes moving the multi-leaf collimator through a first arc while delivering radiation through the first treatment field to the treatment area The multi-leaf collimator is then rotated about a central axis extending generally perpendicular to a plane containing at least a portion of the leaves and the leaves are positioned to define a second treatment field. The method further includes moving the multi-leaf collimator through a second arc while delivering radiation through the second treatment field to the treatment area.
The leaves may also be moved longitudinally after moving the multi-leaf collimator through the arc to define additional treatment fields. In a preferred embodiment, the first and second arcs have the same geometry and the same starting and ending positions.
The method may further include dividing the treatment area into a plurality of cells each having a defined treatment intensity level. The cells are grouped to form a plurality of matrices, each of the matrices having at least one dimension approximately equal to a width of a collimator leaf. Each of the matrices is decomposed into orthogonal matrices which are used to define the treatment field.
In another aspect of the invention, a system for delivering radiation from a radiation source to a treatment area comprises a collimator having multiple leaves for blocking radiation from said source and defining an opening between the radiation source and said treatment area The collimator is operable to move through an arc over the treatment area and rotate about a central axis of a radiation beam emitted from the radiation source. The system further includes a controller configured to position the leaves to define a first treatment field, move the collimator through a first arc while delivering radiation through the first treatment field, rotate the collimator about the central axis, position the leaves to define a s
Bruce David V.
Siemens Medical Solutions USA , Inc.
Thomas Courtney
LandOfFree
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