X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
1999-12-08
2001-11-06
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S064000, C250S492300
Reexamination Certificate
active
06314159
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a radiation emitting device, and more particularly, to a system and method for efficiently 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.
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. 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.
Accordingly, there is therefore, a need for a system and method for achieving higher spatial resolution intensity modulation radiation therapy without changing current multi-leaf collimator leaf widths and an optimization for such a system and method to minimize treatment time.
SUMMARY OF THE INVENTION
A method and system for controlling radiation delivery from a radiation source to an object are disclosed.
A method of the present invention generally comprises defining a field on the object for radiation delivery. The field includes a plurality of cells, each having a defined treatment intensity level. The cells are grouped to form a matrix having at least one dimension approximately equal to a width of a collimator leaf capable of blocking radiation emitted from the radiation source. The method further includes decomposing the matrix into orthogonal matrices and optimizing delivery of the radiation by selecting the orthogonal matrices having minimum vertical and horizontal gradients when combined with adjacent cells within the field.
A system of the present invention generally comprises a collimator having multiple leaves for blocking radiation from the source and defining an opening between the radiation source and object. The system further includes a processor for receiving a matrix comprising a plurality of cells having at least one dimension approximately equal to a width of one of the collimator leaves, decomposing the matrix into orthogonal matrices, and optimizing delivery of the radiation output by selecting the orthogonal matrices having minimum vertical and horizontal gradients when combined with adjacent cells within the field.
The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages, and embodiments of the invention will be apparent to those skilled in the art from the following description, drawings, and claims.
REFERENCES:
patent: 5663999 (1997-09-01), Siochi
patent: 5724403 (1998-03-01), Siochi et al.
patent: 6134296 (2000-10-01), Siochi
Kim Robert H.
Siemens Medical Systems Inc.
Thomas Courtney
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