X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
2001-09-20
2004-03-30
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S901000
Reexamination Certificate
active
06714620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to radiation therapy. Embodiments of the invention are implemented as a software system, called NXEGS, that uses Monte Carlo simulation of radiation transport for radiotherapy treatment planning (RTP) and includes the following capabilities: commissioning of a linear accelerator to construct an equivalent source model, simulation of radiation transport through beam modifiers, and simulation of radiation transport in a patient or phantom to obtain the resulting dose distribution. Embodiments of the invention are implemented using a digital computer programmed to execute the NXEGS software and algorithms described herein.
2. Description of Related Art
The following background citations will be referred to by the references indicated in brackets. The entirety of all of these citations are incorporated herein by reference.
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About 1,400,000 people in the US are diagnosed with cancerous tumors each year. Every American has roughly a 50% chance of contracting some form of cancer during their lifetime, and the number of cases is anticipated to rise substantially in the years to come. Roughly 50% of those diagnosed are treated with radiation in the form of high energy electron beams or photon (X-ray) beams.
FIG. 1.1
shows a schematic drawing of the treatment setup. The radiation source is typically a linear accelerator (linac). After it is emitted from the linac, the radiation beam passes through a set of beam modifiers and then on to the patient or phantom. The treatment head, consisting of linac and beam modifiers, is contained in a moveable gantry, whose position and direction are variable.
FIG. 1.2
shows more detail of the components within the treatment head. Following the linac, one finds four moveable jaws (“left” and “right”, “up” and “down”) that determine the width of the photon beam in the plane transverse to the central axis and one or more scrapers used to define the size of the electron beam. Then there are beam modifiers (such as the wedge and port shown in the
FIG. 1.2
) that are used to modify the intensity profile of the beam.
In order to make the treatment more effective, one must plan quantitatively the exposure to radiation in terms of dose amount, time duration and scheduling of treatments. This requires an accurate simulation of the way in which the radiation beams pass through the patient's tissue and interact with the tumor. Typically, multiple radiation beams are used on a patient, and their direction and intensity must be chosen carefully to apply adequate dose to the cancer without harming healthy tissues.
Intensity modulated radiation therapy (IMRT) and other new treatment modalities allow much more aggressive treatment therapies. These might prescribe a high dose to a target that is close to a critical tissue, so that relatively small errors in the dose calculation could be of great clinical significance. Monte Carlo simulation is the most accurate method for computation of radiation dose delivery, and so it is desired for radiotherapy treatment planning (RTP).
The Monte Carlo method for radiation therapy involves direct computational simulation of the physics of particle transport in the transport media (the beam modifiers and the patient). Particles interact with the transport media through atomistic processes, the outcomes of which are chosen randomly using scattering cross-sections. “Monte Carlo” refers to these random choices, which are made with the help of a computerized random number generator.
EGS4
The Monte Carlo computer code EGS4, developed at the Stanford Linear Accelerator (SLAC) and the National Research Council of Canada (NRCC) &l
Caflisch Russel
Goldenfeld Nigel
Gorlachev Gennady
Kalugin Pavel
Mechkov Serguei
Bruce David V.
Foley & Lardner
Numerix, LLC
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