X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
2001-09-25
2003-01-07
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S901000
Reexamination Certificate
active
06504899
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to intensity modulated radiation therapy (IMRT) and in particular to the selection of beam orientations by evaluating each beamlet of the beam at various gantry angles prior to treatment.
BACKGROUND OF THE INVENTION
The goal of radiation therapy is to deliver a prescribed dose of radiation usually in the form of electromagnetic radiation (photons), electrons, neutrons or protons to a treatment target, such as a tumor, while sparing adjacent organs at risk (OARs). Intensity modulated radiation therapy (IMRT) adds a new degree of freedom to the conventional three-dimensional radiation therapy and allows one to achieve a better dose distribution by modulating the intensity profiles of the incident beams. For general information on IMRT the reader is referred to T. Bortfield, et. al,
“X-ray Field Compensation with Multileaf Collimators”, International Journal of Radiation Oncology, Biology, Physics
, Vol. 28, 1994, pp. 723-730; T. R. Mackie, et al., “
Tomotherapy”, Seminars on Radiation Oncology
, Vol. 9, 1999, pp. 108-117; C. C. Ling, et al., “
Conformal Radiation Treatment of Prostate Cancer using Inversely-Planned Intensity Modulated Photon Beams Produced with Dynamic Multileaf Collimation”, International Journal of Radiation Oncology, Biology, Physics
, Vol. 35 (1996), pp. 721-730.
In IMRT treatment planning the angles at which radiation is delivered to the treatment site in the patient's body, commonly called gantry angles and couch angles in the case of non-coplanar beams, are usually pre-selected based on experience and intuition of the operator. The corresponding beam intensity profiles are then optimized under the guidance of an objective function using so-called inverse treatment planning methods. General information on these methods is provided by S. Webb, “
Optimizing the Planning of Intensity-Modulated Radiotherapy”, Physics in Medicine and Biology
, Vol. 39, 1994, pp. 2229-2246; S. V. Spirou and C. S. Chui, “
A Gradient Inverse Planning Algorithm with Dose-Volume Constraints”, Medical Physics
, Vol. 25, 1998, pp. 321-333; R. Mohan, et al., “
The Potential and Limitations of the Inverse Radiotherapy Techniques”, Radiotherapy & Oncology
, Vol. 32, 1994, pp. 232-248; L. Xing, et al., “
Fast Iterative Algorithms for
3D Inverse Treatment Planning”, Medical Physics, Vol. 25, 1998, pp. 1845-1849; and L. Xing and G. T. Y. Chen, “
Iterative Methods for Inverse Treatment Planning”, Physics in Medicine and Biology
, Vol. 41, 1996, pp. 2107-2123.
The prior art teaches numerous approaches to beam orientation selection in conventional radiation therapy and in IMRT. For information on the methods investigated for conventional radiation therapy the reader is referred to the following references: S. Soderstrom, et al., “
Which is the Most Suitable Number of Photon Beam Portals in Coplanar Radiation Therapy”, International Journal of Radiation Oncology, Biology, Physics,
Vol. 33, 1995, pp. 151-159; G. A. Ezzell, “
Genetic and Geometric Optimization of Three-Dimensional Radiation Therapy Treatment Planning”, Medical Physics,
Vol. 23, 1996, pp. 293-305; P. Gokhale, et al., “
Determination of Beam Orientations in Radiotherapy Planning”, Medical Physics
, Vol. 21, 1994, pp. 393-400; M. E. Hosseini-Ashrafi, et al., “
Pre-optimization of Radiotherapy Treatment Planning: An Artificial Neural Network Classification Aided Technique”, Physics in Medicine and Biology,
Vol. 44, 1999, pp. 1513-1528; C. G. Rowbottom, et al., “
Beam Orientation Customization using an Artificial Neural Network”, Physics in Medicine and Biology
, Vol. 44, 1999, pp. 2251-2262; B. C. J. Cho, et al.,
The Development of Target-Eye-View Maps for Selection of Coplanar or Noncoplanar Beams in Conformal Radiotherapy Treatment Planning”, Medical Physics,
Vol. 26, 1999, pp. 2367-2372; S. K. Das, et al., “
Selection of Coplanar or Noncoplanar Beams using Three-dimensional Optimization Based on Maximum Beam Separation and Minimized Non-Target Irradiation”, International Journal of Radiation Oncology, Biology, Physics
, Vol. 38, 1997, pp. 643-655; D. L. McShan, et al., “
Advanced Interactive Planning Techniques for Conformal Therapy: High Level Beam Description and Volumetric Mapping Techniques”, International Journal of Radiation Oncology, Biology, Physics
, Vol. 33, 1995, pp. 1061-1072; C. G. Rowbottom, et al., “
Constrained Customization of Noncoplanar Beam Orientations in Radiotherapy of Brain Tumors”, Physics in Medicine and Biology,
Vol. 44, 1999, pp. 383-399; S. L. Sailer, et al., “
The Tetrad and Hexad: Maximum Beam Separation as a Starting Point for Noncoplanar
3
D Treatment Planning: Prostate Cancer as a Test Case”, International Journal of Radiation Oncology, Biology, Physics,
Vol. 30, 1994, pp. 439-446; G. T. Y. Chen, et al., “
The use of Beam's Eye View Volumetrics in the Selection of Noncoplanar Radiation Portals”, International Journal of Radiation Oncology, Biology, Physics
, Vol. 23, 1992, pp. 153-163; H. -M. Lu, et al., “
Optimized Beam Planning for Linear Accelerator-Based Stereotactic Radiosurgery”, International Journal of Radiation Oncology, Biology, Physics,
Vol. 39, 1997, pp. 1183-1189; M. Goitein, et al., “
Multi-dimensional Treatment Planning: II. Beam's Eye-View, Back Projection, and Projection through CT Sections”, International Journal of Radiation Oncology, Biology, Physics
, Vol. 9, 1983, pp. 789-797; and Carl Graham, et al., “
Improvements in Prostate Radiotherapy from the Customization of Beam Directions”, Medical Physics
, Vol. 25, 1998, pp. 1171-1179.
Beam orientation selection in IMRT is discussed in the following references: J. Stein, et al., “
Number and Orientations of Beams in Intensity-Modulated Radiation Treatments”, Medical Physics
, Vol. 24, 1997, pp. 149-160; M {dot over (A)}sell, et al., “
Optimal Electron and Combined Electron and Photon Therapy in the Phase Space of Complication-Free Cure”, Physics in Medicine and Biology
, Vol. 44, 1999, pp. 235-252; T. Bortfield and W. Schlegel, “
Optimization of Beam Orientations in Radiation Therapy: Some Theoretical Considerations”, Physics in Medicine and Biology,
Vol. 38, 1993, pp. 291-304; A. Pugachev, et al., “
Beam Orientations in IMRT: To Optimize or not to Optimize?”, The Use of Computers in Radiation Therapy, XIII ICCR,
2000, pp. 37-39; S. Soderstrom and A. Brahme, “
Selection of Suitable Beam Orientations in Radiation Therapy using Entropy and Fourier Transform Measures”, Physics in Medicine and Biology
, Vol. 37, 1992, pp. 911-924; A. Pugachev, A. Boyer, L. Xing, “
Beam Orientation Optimization in Intensity-Modulated Radiation Treatment Planning”, Medical Physics
, Vol. 27, 2000, pp. 1238-1245; and M. Braunstein, et al., “
Optimum Beam Configurations in Tomographic Intensity Modulated Radiation Therapy”, Physics in Medicine and Biology
, Vol. 45, 2000, pp. 305-328.
Unfortunately, there exists a complex interdependence or coupling between the gantry angles and the beam intensity profiles. In principle, all one needs to do is to add the gantry angle variables into an objective function and then to optimize the objective function with respect to the gantry angles and the beamlet weights. In practice, this brute-force optimization is computationally intensive and hence not very useful because the search space constituted by gantry angles and the beamlet weights cannot be separated into two independent subspaces because of the coupling mentioned above. In addition, the objective function is a non-convex function of the gantry angles and a stochastic sampling of the gantry angles has to be used to avoid trapping in a local minimum. Consequently, computation time required by a complete optimization becomes prohibitively long, making impractical the use of beam orientation optimization for routing clinical applications.
Due to the above-mentioned obstacles, typical IMRT procedures typically involve choosing “optimal” gantry angles first. Then, the beam intensity profiles are optimized. The influence of a set of gantry angles on the final radiation
Pugachev Andrei
Xing Lei
Bruce David V.
Lumen Intellectual Property Services
The Board of Trustees of the Leland Stanford Junior University
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