Systems and methods for intensity modulated radiation therapy

Patent metadata

Field	Value
Publication number	US-9884206-B2
Application number	US-201615217946-A
Country	US
Kind code	B2
Filing date	Jul 22, 2016
Priority date	Jul 23, 2015
Publication date	Feb 6, 2018
Grant date	Feb 6, 2018

Abstract

Embodiments disclosed herein include methods for performing intensity-modulated radiation therapy on a subject using a plurality of pencil beams. The methods can include generating a treatment plan for intensity-modulated radiation therapy that satisfies dose constraints for each of a plurality of sub-volumes. The treatment plan can be generated using a superiorization technique that reduces total variation in dose space. Additional dose-volume constraints that permit a fraction of treatment doses to violate a prescription by up to a defined percentage of intensity can be used to assist in determining the treatment plan.

First claim

The following is claimed:

1. A method for performing intensity-modulated radiation therapy on a subject using a plurality of pencil beams, the method comprising:
identifying a volume of interest from a representation of the subject, the volume of interest divided into a total number of voxels;
defining a plurality of sub-volumes, wherein a sub-volume comprises a number of contiguous, ordered voxels; and
generating a treatment plan for intensity-modulated radiation therapy that satisfies dose constraints for each voxel within each of the plurality of sub-volumes;
wherein generating the treatment plan comprises:
determining a system of linear equations of the form Ax*=b or linear inequalities of the form b min ≦Ax*≦b max where x* is a first vector comprising elements x i representing an i th component of a solution vector representing an actual intensity of an i th pencil beam, b is a second vector comprising elements b j representing a dose prescribed for a j th dose grid point, b min is a third vector comprising elements b min j representing a minimum dose prescribed for a j th dose grid point, b max is a fourth vector comprising elements b max j representing a maximum dose prescribed for a j th dose grid point, and A is a matrix comprising elements a ij representing a dose delivered by the i th pencil beam of unit intensity to the j th dose grid point; and
determining one or more feasible solutions x* to the system of equations or inequalities using a feasibility-seeking algorithm.

2. The method of claim 1 , wherein determining one or more feasible solutions x* comprises, for each of the plurality of sub-volumes, receiving a threshold number of dose constraints that are allowed to be violated when performing intensity-modulated radiation therapy using the one or more feasible solutions x*.

3. The method of claim 1 , wherein determining one or more feasible solutions x* comprises, for each of the plurality of sub-volumes, providing a threshold proportion of dose constraints that are allowed to be violated when performing intensity-modulated radiation therapy using the one or more feasible solutions x*.

4. The method of claim 1 , wherein determining one or more feasible solutions x* comprises performing repeated projections of iterates of preliminary solution vectors onto convex sets determined by the linear system of equations or inequalities.

5. The method of claim 1 , wherein determining one or more feasible solutions x* comprises defining a cost function or optimization function and determining a gradient of the cost function or optimization function in order to find a local minimum.

6. The method of claim 1 , wherein generating the treatment plan further comprises perturbing the one or more feasible solutions x* to determine a perturbed solution superior to a non-perturbed solution, wherein perturbing the one or more feasible solutions comprises adding a perturbation term to the one or more feasible solutions x* that reduces total variation in dose space.

7. The method of claim 6 , wherein perturbing the one or more feasible solutions comprises adding a perturbation term repeatedly a specified number of times.

8. The method of claim 6 , wherein perturbing the one or more feasible solutions comprises adding a perturbation term repeatedly until a stopping criterion is met.

9. The method of claim 1 , wherein satisfying dose constraints for each voxel within each of the plurality of sub-volumes comprises receiving a first violation constraint, wherein the first violation constraint specifies that no more than a fraction of the total number of voxels in the volume of interest are permitted to receive a dose of radiation greater than a maximum dose constraint or less than a minimum dose constraint.

10. The method of claim 9 , wherein the minimum dose constraint is a scalar value multiplied by the third vector.

11. The method of claim 9 , wherein the maximum dose constraint is zero multiplied by the fourth vector.

12. The method of claim 9 , wherein the maximum dose constraint is a scalar value greater than zero multiplied by the fourth vector.

13. The method of claim 1 , wherein generating the treatment plan comprises determining whether adding a perturbation term yields a solution that is superior to the estimated initial solution.

14. The method of claim 1 , wherein generating the treatment plan comprises the step of determining whether adding a perturbation term yields a solution that reduces total variation in dose space relative to the estimated initial solution.

15. The method of claim 1 , wherein generating the treatment plan comprises determining a dose of radiation from the solution vector x*, the dose of radiation comprising one or more of x-rays, electrons, protons, or ions heavier than protons.

16. A method for performing intensity-modulated radiation therapy, the method comprising:
obtaining a representation of a patient, the representation comprising information about structures within or on the patient;
identifying a target volume in the representation of the patient;
identifying an organ at risk or other non-targeted tissue in the representation of the patient;
dividing the target volume into a first plurality of sub-volumes, wherein dividing the target volume into a first plurality of sub-volumes comprises:
dividing the target volume into a total number of voxels;
selecting a first fractional value corresponding to a ratio of a size of a sub-volume of the target volume to a size of the target volume; and
for each of the first plurality of sub-volumes, defining a sub-volume of the target volume as a group of a number of contiguous voxels, wherein a ratio of the number of contiguous voxels to the total number of voxels is approximately equal to the first fractional value for the sub-volume of the target volume for the target volume receiving a first violation constraint;

for each voxel of the first plurality of sub-volumes, receiving a prescribed dose and a minimum dose constraint;
selecting a radiation treatment plan that satisfies the first violation constraint, wherein the first violation constraint defines a fraction of the total number of voxels in the target volume that are permitted to receive a dose of radiation below the minimum dose constraint; and
delivering radiation to the patient based on the selected radiation treatment plan.

17. The method of claim 16 , wherein delivering radiation to the patient includes delivering protons, electrons, x-rays, or ions heavier than protons.

18. The method of claim 16 , wherein the minimum dose constraint is a scalar value multiplied by a vector comprising elements representing the minimum prescribed dose for each voxel in the group of contiguous voxels.

19. The method of claim 16 , further comprising the step of dividing the organ at risk or other non-targeted tissue into a second plurality of sub-volumes, the step comprising:
dividing the organ at risk or other non-targeted tissue into a total number of voxels;
selecting a second fractional value corresponding to a ratio of a size of a sub-volume of the organ at risk or other non-targeted tissue to a size of the organ at risk or other non-targeted tissue; and
for each of the second plurality of sub-volumes, defining a sub-volume as a group of a number of contiguous voxels, wherein a ratio of the number of contiguous voxels to the total number of voxels is approximately equal to the second fractional value for the sub-volume.

20. The method of claim 19 , further comprising

Assignees

• Univ Loma Linda
• Censor Yair
• Loma Linda Univ Medical Center
• Carmel Haifa Univ Economic Corporation Ltd

Inventors

• Schulte Reinhard W
• Censor Yair

Classifications

• A61N5/1042 Primary

  with spatial modulation of the radiation beam within the treatment head · CPC title

• A61N5/103

  Treatment planning systems · CPC title

• A61N2005/1087

  Ions; Protons · CPC title

• A61N5/1084

  for delivering multiple intersecting beams at the same time, e.g. gamma knives · CPC title

• A61N2005/1089

  Electrons · CPC title