Radiation therapy treatment method

A method of commissioning a radiation source for use in radiation therapy comprising the steps of:

• (a) positioning a phantom to receive radiation from a said source;
• (b) exposing said phantom to radiation from said source,
• (c) measuring the radiation dose in said phantom resulting from the exposing step,
• said dose measured at a plurality of points within said phantom,
• at least some of said points being axial points located at positions along a substantially central axis of said radiation source and others of said points being transverse points located at positions along an axis transverse to the central axis,
• (d) performing a Monte Carlo simulation of said radiation source to determine a simulated dose at said plurality of points;
• and
• (e) modeling said radiation source using said simulated dose and said measured dose.

A method of commissioning a radiation source comprising the steps of:

• (a) inputting;
• measured dose data into a data processor, said measured dose data derived from:
• (i) exposing said phantom to radiation from said source;
• and
• (ii) measuring the radiation dose to obtain a measured dose in said phantom resulting from the exposing step, said measured dose measured at a plurality of points within said phantom, at least some of said points being axial points located at positions along a substantially central axis of said radiation source and others of said points being transverse points located at positions along an axis transverse to the central axis,
• (b) performing a Monte Carlo simulation of said radiation source to determine a simulated dose at said plurality of points;
• and
• (c) modeling said radiation source using said simulated dose and said measured dose.

A method of commissioning a radiation source comprising the steps of:

• (a) positioning a phantom to receive radiation from a said source;
• (b) exposing said phantom to radiation from said source,
• (c) measuring the radiation dose in said phantom resulting from the exposing step,
• said dose measured at a plurality of points within said phantom,
• at least some of said points located along a central axis of said radiation source and others of said points located along an axis transverse to the central axis,
• (d) performing a Monte Carlo simulation of said radiation source to determine a simulated dose at said plurality of points;
• and
• (e) modeling said radiation source using said simulated dose and said measured dose.

A method of modeling a radiation source, emitting radiation in the form of particles comprising the steps of:

• (a) defining at least one simulated sub-source comprising one of a focal source and an extra focal source;
• each simulated sub-source having a relatively small interval of energy values and a relatively small interval of angular values,
• (b) performing a Monte Carlo simulation of particles leaving said at least one simulated sub-source to determine a simulated dose distribution;
• and
• (c) determining a phase space distribution of radiation leaving said at least one simulated sub-source using said simulated dose distribution and actual dose measurements.

A method of modeling a radiation source, emitting particles, in a linear accelerator used for radiation therapy comprising:

• (a) defining at least one simulated sub-source from the group of simulated sub-sources consisting of a focal source and an extra focal source;
• (b) performing a Monte Carlo simulation of radiation leaving said at least one simulated sub-source to determine a simulated dose distribution;
• and
• (c) determining a phase space distribution of radiation in an exit plane of said linear accelerator using said simulated dose distribution and actual dose measurements.

A method of performing radiation planning therapy comprising the steps of:

• (a) performing a CT scan of a patient to provide patient-dependent information in a region of the patient to be treated;
• (b) utilizing a source model based on dosimetry data which includes at least 10 dosimetry points;
• (c) providing treatment head information concerning the characteristics and geometry of a treatment head;
• and
• (d) simulating a dose distribution using a Monte Carlo calculation based on a source model, the patient-dependent information and the treatment head information.

A method of simulating radiation transport through a treatment head of a linear accelerator, said treatment head having at least one beam modifier, said method comprising the steps of:

• (a) inputting into a data processor, parameters corresponding to a physical description of the treatment head and the at least one beam modifier included in the treatment head;
• (b) simulating the introduction of particles from a source into the treatment head;
• and
• (c) performing simulated transport of particles through the at least one beam modifier in the treatment head through at least one of a Monte Carlo method or a throughput function.

A method of radiation treatment planning comprising the steps of:

• (a) performing one of (1) commissioning a linear accelerator to obtain a source model or (2) using a source model from a linear accelerator that has already been commissioned, wherein said commissioning includes utilizing at least 10 dosimetry points;
• (b) simulating one or more beams based on a source model;
• (c) specifying a simulated treatment head, including (1) geometry and (2) material properties of at least one beam modifier for each beam;
• (d) setting up a simulated patient or a simulated phantom;
• (e) simulating particle transport through the simulated treatment head using at least one of a Monte Carlo method or a throughput function for each beam;
• (f) simulating particle transport through the simulated patient or simulated phantom using said Monte Carlo method;
• (g) calculating a radiation dose in the simulated patient or simulated phantom;
• and
• (h) providing an output of the calculated dose.

A method of radiation treatment planning comprising the steps of:

• (a) simulating one or more beams based on a source model;
• (b) specifying a simulated treatment head, including (1) geometry, (2) motion and (3) material properties of at least one beam modifier for each beam;
• (c) setting up a simulated patient or a simulated phantom;
• (d) simulating particle transport through the simulated treatment head using at least one of a Monte Carlo method or a throughput function for each beam;
• (e) simulating particle transport through the simulated patient or simulated phantom using Monte Carlo method;
• (f) calculation a radiation dose in the simulated patient or simulated phantom;
• and
• (g) providing an output of the calculated dose.

A method of specifying at least one beam modifier for use in Monte Carlo simulation of a particle motion through a treatment head which includes a radiation source and at least one beam modifier, said method comprising the steps of:

• (a) inputting into a data processor a geometry specifying said at least one beam modifier by performing at least one of the following three steps:
• (i) for a beam modifier in the shape of a polyhedron, inputting the coordinates of each vertex of said polyhedron and specifying the edges of connecting vertices, and inputting the position and orientation of the polyhedron;
• (ii) for a beam modifier in the form of a multi-leaf collimator, inputting the number and size of each leaf;
• and
• (iii) for a beam modifier in the shape of a compensating filter, consisting of a flat side and a curved shape of arbitrary complexity opposite the flat side, inputting the height of the curved shape above each point of the flat side, and specifying whether the flat side points toward or away from the radiation source;
• and
• (b) inputting a type and density of material that constitutes said at least one beam modifier.

A method of performing radiation planning therapy comprising the steps of:

• (a) performing a CT scan of a patient to provide patient-dependent information in a region of the patient to be treated;
• (b) providing treatment head information concerning the characteristics and geometry of a treatment head;
• (c) simulating a dose distribution using a Monte Carlo calculation based on a source model, the patient-dependent information and the treatment head information;
• and
• (d) wherein, as part of step (b), the method include specifying at least one beam modifier for use in said Monte Carlo calculations of particle motion through said treatment head which includes a radiation source and said at least one beam modifier, said step of specifying including:
• (i) inputting into a data processor a geometry specifying said at least one beam modifier by performing at least one of the following three steps:
• (1) for a beam modifier in the shape of a polyhedron, inputting the coordinates of each vertex of said polyhedron and specifying the edges of connecting vertices, and inputting the position and orientation of the polyhedron;
• (2) for a beam modifier in the form of a multi-leaf collimator, inputting the number and size of each leaf;
• and
• (3) for beam modifier in the shape of a compensating filter, consisting of a flat side and a curved shape of arbitrary complexity opposite the flat side, inputting the height of the curved shape above each point of the flat side, and specifying whether the flat side points toward or away from the radiation source;
• and
• (ii) inputting a type and density of material that constitutes said at least one beam modifier.

A method for computing the dose deposition due to particles whose energy is below a cutoff, as part of a Monte Carlo simulation, comprising the steps of:

• (a) determining that a given particle has reached a cutoff energy within a given voxel;
• and
• (b) for particles below the cutoff energy, performing the steps of:
• (i) extending the particle path in a straight path from the point at which the cutoff was reached in the direction of the particle motion at said point;
• and
• (ii) simulating a constant energy deposition rate using a rate constant along said straight path.

A method of simulating the transport of electrons using a Monte Carlo calculation comprising the steps of:

• (a) for a given energy of a simulated particle, determining a step size in the Monte Carlo calculation to correspond to a fixed number of elastic scatterings wherein said step size is between an initial and end position and the particle path is a straight path between said initial and end positions;
• (b) determining whether a discrete event occurs along said particle path based on the cross section of the particle within the material through which the particle path traverses;
• (c) if a discrete event does not occur along the particle path, then
• (i) randomly selecting a first intermediate point between the initial position and the end position along said particle path;
• (ii) determining a scattering angle at the first intermediate point based on a tabulated cross section of the material existing at the first intermediate point;
• (iii) simulating a Molière scattering event at the first intermediate point with the determined scattering angle, said Molière scattering corresponding to said fixed number of elastic scatterings;
• and
• (iv) said scattering angle determining a new end point for the particle path.

A method for commissioning a source model for an electron beam wherein the source model includes a focal electron subsource and a focal photon subsource, both lying on the central axis of a linear accelerator, wherein said source model includes a sampling plane perpendicular to the central axis in which simulated electrons and photons are specified by their position r from the central axis and their energy E, wherein the position r defines an angle theta, and the position r is randomly selected and the particle is assigned a weight through fluence functions for the electron and photon subsources and the energy E is determined through energy spectra for the electron and photon subsources, said method comprising the steps of:

• (a) selecting an initial estimate for:
• (i) positions of the electron and photon subsource along the central axis;
• (ii) parameters defining the energy spectra for the electrons and photons;
• and
• (iii) parameters defining the fluence functions for the electrons and photons;
• and
• (b) using the initial estimate, simulating a plurality of dose distributions, including output factors, percentage depth dose (PDD) curves, and dose profiles;
• (c) comparing the simulated output factors to the measured output factors and determining an improved estimate for the positions of the electron and photon subsource along the central axis;
• (d) comparing the simulated PDD curves to the measured PDD curves and determining an improved estimate for the parameters defining the energy spectra for the electrons and photons;
• and
• (e) comparing the simulated dose profiles to the measured dose profiles and determining an improved estimate for the parameters defining the fluence functions for the electrons and photons.

A method for defining a source model for an electron beam wherein the source model includes the following:

• (a) defining a focal electron subsource lying on the central axis of a linear accelerator;
• (b) defining focal photon subsource lying on the central axis of the linear accelerator;
• (c) defining a sampling plane perpendicular to the central axis;
• (d) specifying fluence functions, which are functions of the position r from the central axis, for each of electrons and photons;
• (e) specifying energy spectra for each of said electrons and photons;
• (f) determining the direction of each of said electrons and photons by the straight line direction from the respective focal subsource location to a point in the sampling plane;
• and
• (g) specifying a scattering of electrons by varying the direction of said electrons from the determined direction from step f).

A method for commissioning a source model for a photon beam wherein the source model includes a focal photon subsource and a focal electron subsource, both lying on the central axis of a linear accelerator, and an extrafocal photon subsource lying on a plane perpendicular to the central axis, wherein said source model includes a sampling plane perpendicular to the central axis in which simulated electrons and photons are specified by their position r from the central axis and their energy E, wherein the position r defines an angle theta, and the position r is randomly selected and the particle is assigned a weight through fluence functions for the electron and photon subsources and the energy E is determined through energy spectra for the electron and photon subsources, said method comprising the steps of:

• (a) determining the spatial distribution of said extrafocal photon subsource to fit output factors in air;
• (b) performing Monte Carlo simulation of radiation transport for a plurality of beamlets, each of which corresponds to subset of energies and angles for said focal photon subsource or said focal electron subsource, and obtaining simulated dose values at each point of a phantom for which there are measured dose values;
• and
• (c) using a matrix of said simulated dose values in determining the spectrum and fluence for said focal photon subsource or said focal electron subsource to fit the measured dose values.

A method for defining a source model for a photon beam wherein the source model includes the following:

• (a) defining a focal photon subsource lying on the central axis of a linear accelerator;
• (b) defining a focal electron subsource lying on the central axis of the linear accelerator;
• (c) defining an extrafocal photon subsource lying on a plane perpendicular to the central axis of the linear accelerator;
• (d) defining a sampling plane perpendicular to the central axis;
• (e) specifying fluence functions, which are functions of the position r from the central axis, for each of the electron and photon subsources;
• (f) specifying energy spectra for each of the electron and photon subsources;
• (g) selecting a point in the sampling plane for each electron from the focal electron subsource, each photon from the focal photon subsource and each photon from the extrafocal photon subsource;
• (h) selecting a point on the plane of the extrafocal photon subsource;
• (i) determining the direction of said photon from the focal photon subsource and said electron from the focal electron subsource by the straight line direction from the respective focal subsource location to the respective point in the sampling plane;
• (j) determining the direction of said photon from the extrafocal photon subsource by the straight line direction from said point on the plane of the extrafocal photon subsource to the respective point in the sampling plane;
• and
• (k) specifying a scattering of electrons by varying the direction of said electrons from the determined direction from step i).

A method of error reduction of Monte Carlo simulation radiation transport comprising the steps of:

• (a) calculating a dose distribution fS(x) using a first Monte Carlo simulation using a number, n, of particles and a random number sequence;
• (b) calculating a dose distribution gS(x) based on a simplified representation of the radiation transport using a second Monte Carlo simulation with said number of particles n and said random sequence;
• (c) calculating a dose distribution gL(x) based on said simplified representation using a third Monte Carlo simulation with a number of particles m where m is greater than n;
• and
• (d) reducing the error in the dose distribution fS(x) by using fS(x)−gS(x)+gL(x) as the error reduced dose distribution.

A method of accelerating computation of dose distributions in a target area comprising the steps of:

• (a) mathematically constructing a fine grid throughout regions of said target area where the density of the target area is non-uniform;
• (b) mathematically constructing a coarse grid throughout regions of said target area where the density of the target area is uniform;
• and
• (c) performing a Monte Carlo simulation of the dose distribution using transport steps defined within said coarse and fine grids wherein in said coarse grid, larger transport steps are used relative to transports steps used in said fine grid.

A method of improving the accuracy of a Monte Carlo simulation in radiation treatment planning for particle transport within a target region of interest comprising the steps of:

• (a) selecting an end point position within the target region of interest;
• (b) selecting an initial position outside of the target region;
• (c) selecting at least one intermediate point on a particle path connecting the initial and end positions randomly chosen using a bi-directional probability distribution;
• (d) repeating step c) for multiple particle paths having different intermediate points;
• and
• (e) calculation the total dose within the target region resulting from the summation or average of the doses of the multiple paths.

A method of improving the simulation of a Compton scattering event in computing dose distributions of radiation resulting from Compton scattering events comprising the steps of:

• (a) performing a Monte Carlo transport simulation using an electromagnetic source;
• (b) determining Compton scattering events along a simulated transport path of said radiation in a treatment region of interest;
• and
• (c) at each Compton scattering event, simulating the generation of a plurality of electrons distributed along the transport path.