X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
2001-05-18
2002-09-10
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
Reexamination Certificate
active
06449336
ABSTRACT:
BACKGROUND OF THE INVENTION
The field of the invention is a system and method for optimizing intensity-modulated radiation therapy (IMRT) delivery systems.
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 that can be swiveled around a horizontal axis of rotation in the course of a therapeutic treatment. A linear accelerator is, e.g., located in the gantry for generating a high-energy radiation beam for therapy. During treatment, this radiation beam is trained on a zone of a patient lying in the isocenter of the gantry rotation.
The point of such therapy is to concentrate radiation on tumors or other target zones, but minimize radiation dosages applied to adjacent healthy tissue, especially certain parts of the body (e.g., the optic nerve) that are more sensitive to radiation. A radiation source directs radiation towards the target zone. By moving the radiation source along an arc over a period of time, the radiation is on the target during the entire movement along the arc. However, healthy tissue adjacent the tumor (such as between the tumor and source, and tissue past the tumor along the beam path) receive radiation for only a small portion of the time, different sections of healthy tissue being in the radiation path at different places along the arc. Additionally, the patient is moved (usually rotated about a vertical axis) to achieve the same effect (i.e., radiation stays on the target during the entire treatment time, but healthy tissue is only exposed for a small fraction of the treatment time). Thus, the total radiation applied to the target may achieve the desired result, but the reduced radiation applied to adjacent tissue avoids or minimizes damage to the healthy tissues.
An important factor in such radiation treatment is maintaining the beam from the radiation source on the target zone. Precise positioning of the radiation source relative to the patient is thus required. The time of treatment affects the accuracy of the beam. A longer treatment time increases the chances that the patient or portion of the patient will move. Therefore, a shorter period of treatment is generally preferable because the chances of movement occurring is reduced.
To control the radiation emitted toward an object, a beam shielding device, such as a plate arrangement or a collimator, is typically provided in the trajectory of the radiation beam between the radiation source and the object. An example of a plate arrangement is a set of, e.g., four plates that can be used to define an opening for the radiation beam. A collimator is a beam-shielding device that could include multiple leaves, for example, a plurality of relatively thin plates or rods, typically arranged as opposing leaf pairs. The plates themselves 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 object to which a prescribed amount of radiation is to be delivered. The usual treatment field shape results in a three-dimensional treatment volume that 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 organs surrounding and overlying the tumor determines the dosage that can be delivered to the tumor.
The delivery of radiation by a radiation therapy device is prescribed and approved by an oncologist, a doctor specializing in cancer and its treatment. The prescription is a definition of, for example, a particular volume and the level of radiation permitted to be delivered to that volume. A therapist, however, normally carries out actual operation of the radiation equipment. When the therapist administers the actual delivery of the radiation treatment as prescribed by the oncologist, the radiation-emitting device is programmed to deliver that specific treatment. When programming the 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.
Modern day radiation therapy of, e.g., 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 that 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.
Intensity modulated treatment is a specialized technique for radiation treatment. Usually, the beam-shielding device in intensity modulated treatment includes either (1) two pairs of opposing jaws or (2) a pair of jaws and a pair of opposing sets of multi-leaf collimator leaves. One pair of these jaws or the pair of multi-leaf collimator leaves move in the same direction at different speeds. This creates a sweeping opening for the radiation beam. Because the jaws (or leaves) are traveling at different speeds, the opening varies in size during the sweeping. Usually, elaborate speed control and thick jaws (or leaves) are needed for intensity modulated treatment. The speed control is needed for accurately defining the changing opening size. The thick jaws (or leaves) are needed because of a concern with radiation leakage. For example, due to the sweeping treatment, approximately three times the regular amount of radiation dose is needed to treat an area on a patient. Therefore, the radiation leakage for intensity modulated treatment is approximately three times greater than regular leakage. For example, a regular treatment of 100 monitor units (MU) of radiation results in approximately 0.1 MU of radiation leakage. With an intensity modulated treatment for the same field, 300 MU of radiation is required and results in 0.3 MU of radiation leakage.
Intensity modulated treatment usually utilizes a multi-leaf collimator. The multi-leaf collimator can be in addition to the jaws, replace a pair of jaws, or replace all of the jaws. This collimator is typically rotated around the patient during the radiat
Kim Siyong
Palta Jatinder
Church Craig E.
Clarke Dennis P.
Miles & Stockbridge
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