Treatment plan optimization method for radiotherapy

1. A method in treatment planning for radiosurgery, comprising:

defining a first region and a boundary associated with the first region;

selecting a plurality of beam aperture points around the first region, each beam aperture point associated with an intensity level and shape of a radiation beam;

determining a dose distribution in the first region and a low dose level to the boundary associated with the first region, the low dose level applied to the boundary associated with the first region having a level that is less than a lowest dose level in the dose distribution applied to the first region, the determining step including calculating a gradient objective for controlling the low dose level applied to the boundary associated with the first region; and

iteratively optimizing the intensity or shape of the radiation beam at each beam aperture point if a gradient objective curve associated with the gradient objective indicates a better value.

2. The method as recited in claim 1 , wherein the iteratively optimizing step comprises removing a changed value of intensity or shape of the radiation beam at a particular beam aperture point if the gradient objective curve associated with the gradient objective indicates a worse value.

3. The method as recited in claim 1 , wherein the determining step comprises computing the dose distribution in the first region and the boundary associated with the first region against a desired exposure criteria.

4. The method as recited in claim 1 , wherein the dose distribution comprises a first dose range and a second dose range, the first dose range applied to the first region including a high percentage of a prescribed dose, and the second dose range applied to a second region including a low percentage of the prescribed dose.

5. The method as recited in claim 1 , wherein the selecting step comprises the plurality of beam aperture points being selected along a trajectory around the first region.

6. The method as recited in claim 1 , further comprising adjusting the intensity of the radiation beam at each beam aperture point along a trajectory around the first region.

7. The method as recited in claim 1 , further comprising adjusting the shape of the radiation beam at each beam aperture point along a trajectory around the first region.

8. The method as recited in claim 1 , wherein the shape of the radiation beam for each beam aperture point is configured by an aperture, the aperture having a plurality of movable leaves forming at least one opening, the plurality of leaves being disposed to match a projection of the first region.

9. The method as recited in claim 8 , wherein the plurality of moveable leaves on the aperture move in a direction that provides the at least one opening, the plurality of moveable leaves including a plurality of leaf pairs where each leaf pair has a first leaf and a second leaf.

10. The method as recited in claim 9 , wherein each leaf comprises a plate having a thickness extending in a direction that is perpendicular to the radiation beam.

11. The method as recited in claim 1 , further comprising selecting a second plurality of beam aperture points.

12. The method as recited in claim 1 , wherein the defining step comprises defining a second region, the boundary located between the first region and the second region.

13. The method as recited in claim 12 , wherein the second region comprises a critical area.

14. The method as recited in claim 1 , wherein the first region comprises a target area.

15. The method as recited in claim 14 , wherein the target area comprises a tumor, an area in a brain, or a neck area.

16. The method as recited in claim 1 , wherein the first region is located within a subject.

17. A radiation treatment system, comprising:

an aperture having a plurality of leaves and configured to shape a radiation beam directed at a treatment volume;

a gantry configured to move the plurality of leaves in the aperture around the treatment volume; and

a computing device configured to:

defining a first region and a boundary associated with the first region;

selecting a plurality of beam aperture points around the first region, each beam aperture point associated with an intensity level and shape of a radiation beam; and

determining a dose distribution in the first region and a low dose level to the boundary associated with the first region, wherein the low dose level applied to the boundary associated with the first region has a level that is less than a lowest dose level in the dose distribution applied to the first region, the determining step including calculating a gradient objective for controlling the low dose level applied to the boundary associated with the first region; and

iteratively optimizing the intensity or shape of the radiation beam at each beam aperture point if a gradient objective curve associated with the gradient objective indicates a better value.

18. A method in treatment planning for radiosurgery, comprising:

defining a first region and a boundary associated with the first region;

selecting a plurality of beam aperture points around the first region, each beam aperture point associated with an intensity level and shape of a radiation beam;

determining a dose distribution in the first region and a low dose level to the boundary associated with the first region, the low dose level applied to the boundary associated with the first region having a level that is less than a lowest dose level in the dose distribution applied to the first region, the determining step including calculating a gradient objective for controlling the low dose level applied to the boundary associated with the first region; and

iteratively optimizing the intensity or shape of the radiation beam at each beam aperture point if a gradient objective curve associated with the gradient objective indicates a better value, the iteratively optimizing step including removing a changed value of intensity or shape of the radiation beam at a particular beam aperture point if the gradient objective curve associated with the gradient objective indicates a worse value.

19. A method in treatment planning for radiosurgery, comprising:

defining a first region and a boundary associated with the first region;

selecting a plurality of beam aperture points around the first region, each beam aperture point associated with an intensity level and shape of a radiation beam;

determining a dose distribution in the first region and a low dose level to the boundary associated with the first region, the low dose level applied to the boundary associated with the first region having a level that is less than a lowest dose level in the dose distribution applied to the first region, the determining step including calculating a gradient objective for controlling the low dose level applied to the boundary associated with the first region,

wherein the gradient objective is computed as a sigmoid function:

dose( x )=1/[1+exp(− tx )],

where x denotes a distance from the border.

20. A method in treatment planning for radiosurgery, comprising:

defining a first region and a boundary associated with the first region;

selecting a plurality of beam aperture points around the first region, each beam aperture point associated with an intensity level and shape of a radiation beam;

determining a dose distribution in the first region and a low dose level to the boundary associated with the first region, the low dose level applied to the boundary associated with the first region having a level that is less than a lowest dose level in the dose distribution applied to the first region, the determining step including calculating a gradient objective for controlling the low dose level applied to the boundary associated with the first region; and

optimizing the intensity or shape of the radiation beam at each beam aperture point if a gradient objective curve associated with the gradient objective indicates a better value.