Multi level multileaf collimators

1. A multileaf collimator comprising:

a first set of a plurality of pairs of beam blocking leaves arranged adjacent one another, leaves of each pair in the first set being disposed in an opposed relationship and longitudinally movable relative to each other in a first direction; and

a second set of a plurality of pairs of beam blocking leaves arranged adjacent one another, leaves of each pair in the second set being disposed in an opposed relationship and longitudinally movable relative to each other in a second direction generally parallel to the first direction; wherein

the first and second sets of pairs of leaves are disposed in different planes,

each of the first and second sets includes an inner first section of a plurality of pairs of leaves having a first cross section and an outer second section of a plurality of pairs of leaves having a second cross section, and

the first cross section of the leaves in the first section of the first set is thinner than the first cross section of the leaves in the first section of the second set; and

wherein the second section in each of the first and second sets includes a plurality of pairs of leaves at each side of the inner first section.

2. The multileaf collimator of claim 1 wherein the second cross section of the leaves in the second section of the first set is thinner than the second cross section of the leaves in the second section of the second set.

3. The multileaf collimator of claim 1 wherein the first cross section of the plurality of leaves in the first section of the first set is thinner than the second cross section of the plurality of leaves in the second section of the first set, and/or the first cross section of the plurality of leaves in the first section of the second set is thinner than the second cross section of the plurality of leaves in the second section of the second set.

4. The multileaf collimator of claim 3 wherein the leaves in each of the second sections of the first and second sets are symmetrically disposed relative to each of the first sections of the first and second sets respectively.

5. A multileaf collimator, comprising:

a first set of a plurality of pairs of beam blocking leaves arranged adjacent one another, leaves of each pair in the first set being disposed in an opposed relationship and longitudinally movable relative to each other in a first direction; and

a second set of a plurality of pairs of beam blocking leaves arranged adjacent one another, leaves of each pair in the second set being disposed in an opposed relationship and longitudinally movable relative to each other in a second direction generally parallel to the first direction;

wherein the first and second sets of pairs of leaves are disposed in different planes, and the leaves in the first and second sets substantially focus on a converging virtual point located substantially at a radiation source; and

wherein the leaves in the first and second sets have a substantially trapezoidal cross section where the parallel sides of the trapezoidal cross-section have different dimensions, and

the leaves in the first set include a main portion having a height and an end portion having a curved end surface extended beyond the height of the main portion.

6. The multileaf collimator of claim 5 wherein the leaves in the first and second sets have generally flat side surfaces.

7. The multileaf collimator of claim 5 wherein each leaf in the first set is offset from a leaf in the second set in a direction generally transverse to the first and second directions.

8. The multileaf collimator of claim 5 wherein the first set has a first number of pairs of leaves, and the second set has a second number of pairs of leaves different from the first number.

9. The multileaf collimator of claim 5 wherein the leaves in the first set have a first cross section and the leaves in the second sets have a second cross section different from the first cross section.

10. The multileaf collimator of claim 5 wherein the leaves in the first and second sets are supported by one or more movable carriages.

11. The multileaf collimator of claim 5 wherein the leaves in the first set include a main portion having a height and an end portion having one or two projections extended beyond the height of the main portion.

12. A multileaf collimator, comprising:

a first set of a plurality of pairs of beam blocking leaves arranged adjacent one another, leaves of each pair in the first set being disposed in an opposed relationship and longitudinally movable relative to each other in a first direction; and

a second set of a plurality of pairs of beam blocking leaves arranged adjacent one another, leaves of each pair in the second set being disposed in an opposed relationship and longitudinally movable relative to each other in a second direction generally parallel to the first direction;

wherein the first and second sets of pairs of leaves are disposed in different planes, and each leaf in the first set is offset from a leaf in the second set by about half a leaf width in a direction generally traverse to the first and second directions, and

wherein each leaf in the first set has a substantially same first cross-section, and each leaf in the second set has a substantially same second cross-section, and the first cross-section is different from the second cross-section.

13. The multileaf collimator of claim 12 wherein a quantity of the leaves in the first set is different from a quantity of the leaves in the second set.

14. The multileaf collimator of claim 12 wherein the leaves in the first and second sets are arranged to substantially focus on a single converging point.

15. The multileaf collimator of claim 12 wherein the leaves in the first and second sets have a substantially trapezoidal cross section.

16. The multileaf collimator of claim 15 wherein the leaves in the first and second sets have generally flat side surfaces.

17. The multileaf collimator of claim 12 wherein the leaves in the first and second sets are supported by one or more movable carriages.

18. The multileaf collimator of claim 12 wherein the leaves in the first set include a main portion having a height and an end portion having a curved end surface extended beyond the height of the main portion.

19. The multileaf collimator of claim 12 wherein the leaves in the first set include a main portion having a height and an end portion having one or two projections extended beyond the height of the main portion.

20. A method of shaping radiation beams from a radiation source, comprising:

providing a multileaf collimator between a radiation source and an isocenter, said multileaf collimator comprising first and second sets of a plurality of beam blocking leaves disposed in first and second planes, leaves in each of the first and second sets being arranged in two opposing arrays forming a plurality of pairs of leaves in the first and second sets respectively, leaves of each pair being arranged in an opposed relationship and longitudinally movable relative each other, and the longitudinal moving directions being substantially parallel generally traverse to a beam direction; and

moving selected pairs of leaves in the first and second sets from the two opposing arrays in a substantially parallel direction to close ends of opposing leaves of the selected pairs to block a selected portion of a radiation beam;

wherein in moving the selected pairs of leaves to close the ends of opposing leaves to block the selected portion of the radiation beam, a pair of leaves in the first set close at a first location, a corresponding pair of leaves in the second set close at a second location, and the first and second locations are offset from a beam's point of view.

21. The method of claim 20 wherein at the first location, the pair of leaves in the first set are in contact.

22. The method of claim 21 wherein at the second location, the pair of leaves in the second set are in contact.