X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
2000-08-23
2001-12-11
Kim, Robert H. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S147000
Reexamination Certificate
active
06330300
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a radiation emitting device, and more particularly, to a system and method 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.
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.
Another possible solution is to define intensity maps with a very small cell size (e.g. 2 mm in the direction of movement of the leaf). One drawback to this is that the intensity map becomes very complex with many of the high resolution cells providing no benefit since they are not located adjacent critical structures. The high resolution is typically important only at a border of the treatment field, near regions containing critical structures.
Accordingly, there is therefore, a need for a system and method for defining an intensity map that is deliverable with a conventional multi-leaf collimator at a higher spatial resolution.
SUMMARY OF THE INVENTION
A method and system for controlling radiation delivery to a treatment area from a radiation source arc disclosed. In one aspect of the invention, a method generally includes dividing the treatment area into a plurality of cells each having a predefined treatment intensity level and defining an edge margin on at least a portion of the cells. The edge margin has an intensity level different than the predefined intensity level of the cell. The method further includes defining one or more treatment fields by longitudinally positioning leaves of the multi-leaf collimator to block radiation from some of cells. The method further includes adjusting a longitudinal position of leaves of the multi-leaf collimator such that the leaves cover the edge margin in at least one of the treatment fields to reduce the amount of radiation delivered to said edge margin.
The edge margin may be a periphery edge margin for cells located on a border of the treatment area or an internal area within a border of the treatment area that is shielded during radiation delivery.
A system of the present invention generally includes a collimator having multiple leaves for blocking radiation from the radiation source and defining an opening between the radiation source and the treatment area. The system also includes a processor operable to receive cell and edge margin data, position the leaves to define at least one treatment field based on the cell sizes and intensity levels and adjust the leaf positions to reduce the amount of radiation delivered to said edge margins.
The collimator is preferably rotatable about a radiation beam emitted from the radiation source to deliver radiation to a first treatment field with the leaves extending longitudinally along the first axis and a second treatment field with the leaves extending longitudinally along a second axis. The first axis is generally orthogonal to the second axis.
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: 6052430 (2000-04-01), Siochi et al.
patent: 6128366 (2000-10-01), Siochi
patent: 6134296 (2000-10-01), Siochi
Kiknadze Irakli
Kim Robert H.
Siemens Medical Solutions USA , Inc.
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