Online angle selection in rotational imaging and tracking systems

1. A method comprising:

determining a set of angles that have a tracking quality metric value that satisfies a tracking quality metric criterion; and

during an alignment phase or a treatment phase for a treatment stage of a target by a radiation therapy apparatus comprising a gantry that rotates at a speed of over one rotation per minute, performing the following, comprising:

selecting at least a first angle and a second angle from the set of angles for a first rotation of the gantry;

generating, using an imaging device mounted to the gantry, a first tracking image of the target from the first angle during the first rotation of the gantry;

generating, using the imaging device, a second tracking image of the target from the second angle during the first rotation of the gantry; and

performing target tracking based on the first tracking image and the second tracking image.

2. The method of claim 1 , wherein determining the set of angles comprises receiving an ordered list of the set of angles, wherein the first angle has a highest tracking quality metric value from the set of angles, and wherein the second angle has a separation from the first angle of at least an angle separation threshold.

3. The method of claim 1 , further comprising:

generating a third tracking image of the target from the first angle during a second rotation of the gantry;

performing the target tracking based on the third tracking image;

generating a fourth tracking image of the target from the second angle during the second rotation of the gantry; and

performing the target tracking based on the fourth tracking image.

4. The method of claim 1 , further comprising:

determining that the target tracking based on the second tracking image has failed;

continuing the treatment stage of the target;

selecting a third angle from the set of angles;

generating a third tracking image of the target from the third angle; and

performing the target tracking based at least in part on the third tracking image.

5. The method of claim 4 , wherein the third tracking image is generated during the first rotation of the gantry.

6. The method of claim 4 , wherein the third tracking image is generated during a second rotation of the gantry.

7. The method of claim 4 , wherein the third angle has a next highest tracking quality metric value after the second angle.

8. The method of claim 1 , further comprising:

determining that the target tracking based on the second tracking image has failed;

determining a time window within which a next tracking image must be taken;

determining that no angle from the set of angles will be available within the time window; and

interrupting a treatment delivery for the treatment stage.

9. The method of claim 1 , wherein determining the set of angles that have a tracking quality metric value that satisfies the tracking quality metric criterion comprises:

receiving an initial list of candidate angles that satisfied the tracking quality metric criterion during treatment planning;

generating pretreatment images from one or more angles of the initial list of candidate angles prior to the treatment stage; and

determining a subset of the initial list of candidate angles for the treatment stage based on the pretreatment images.

10. The method of claim 1 , wherein determining the set of angles that have the tracking quality metric value that satisfies the tracking quality metric criterion comprises:

determining a plurality of angles used during one or more previous treatment stages of the target; and

selecting two or more angles from the plurality of angles for the treatment stage.

11. The method of claim 1 , wherein determining the set of angles that have a tracking quality metric value that satisfies the tracking quality metric criterion comprises:

performing a computer tomography (CT) scan or a magnetic resonance imaging (MRI) scan of the target;

receiving a delineation of the target in the CT scan or the MRI scan;

generating x-ray images of the target from a plurality of angles;

determining, for each angle of the plurality of angles, the tracking quality metric value for tracking the target based on an analysis of an x-ray image generated at that angle; and

selecting a subset of the plurality of angles that have a tracking quality metric value that satisfies the tracking quality metric criterion.

12. The method of claim 1 , wherein determining the set of angles that have a tracking quality metric value that satisfies the tracking quality metric criterion comprises:

determining a plurality of angles from which tracking images can be generated by the imaging device;

generating a plurality of projections of a treatment planning image of the target, the treatment planning image comprising a delineated target, wherein each projection of the plurality of projections has an angle that corresponds to one of the plurality of angles from which the tracking images can be taken;

determining, for each angle of the plurality of angles, the tracking quality metric value for tracking the target based on an analysis of a projection generated at that angle; and

selecting a subset of the plurality of angles that have a tracking quality metric value that satisfies the tracking quality metric criterion.

13. The method of claim 12 , further comprising:

generating a plurality of x-ray images of the target from two or more angles from the subset of the plurality of angles; and

generating a motion model of the target from the plurality of x-ray images;

wherein determining the set of angles that have a tracking quality metric value that satisfies the tracking quality metric criterion further comprises determining a second subset of the subset of the plurality of angles, wherein the second subset comprises angles associated with projections that are most sensitive to motion of the target as represented in the motion model.

14. A radiation therapy apparatus comprising:

a treatment couch;

a rotatable gantry that is to rotate at a speed of at least one rotation per minute around the treatment couch;

a radiation treatment source mounted to the rotatable gantry, the radiation treatment source to deliver a radiation treatment beam to a target;

an imaging device mounted to the rotatable gantry at a position on the rotatable gantry that is approximately orthogonal to the radiation treatment source, the imaging device to generate tracking images of the target; and

a processing device to control operation of the imaging device for a treatment stage, wherein the processing device is to:

determine a set of angles that have a tracking quality metric value that satisfies a tracking quality metric criterion;

select at least a first angle and a second angle from the set of angles for a first rotation of the rotatable gantry;

cause the imaging device to generate a first tracking image of the target from the first angle during the first rotation of the rotatable gantry;

cause the imaging device to generate a second tracking image of the target from the second angle during the first rotation of the rotatable gantry; and

perform the target tracking based on the first tracking image and the second tracking image.

15. The radiation therapy apparatus of claim 14 , wherein the set of angles is determined from an ordered list of the set of angles, wherein the first angle has a highest tracking quality metric value from the set of angles, and wherein the second angle has a separation from the first angle of at least an angle separation threshold.

16. The radiation therapy apparatus of claim 14 , wherein the processing device is further to:

determine that the target tracking based on the second tracking image has failed;

continue the treatment stage;

select a third angle from the set of angles;

cause the imaging device to generate a third tracking image of the target from the third angle; and

perform the target tracking based at least in part on the third tracking image.

17. The radiation therapy apparatus of claim 14 , wherein the processing device is further to:

determine that the target tracking based on the second tracking image has failed;

determine a time window within which a next tracking image must be taken;

determine that no angle from the set of angles will be available within the time window; and

interrupt a treatment delivery for the treatment stage.

18. The radiation therapy apparatus of claim 14 , wherein to determine the set of angles that have a tracking quality metric value that satisfies the tracking quality metric criterion the processing device is to:

receive an initial list of candidate angles that satisfied the tracking quality metric criterion during treatment planning;

generate pretreatment images from one or more angles of the initial list of candidate angles prior to the treatment stage; and

determine a subset of the initial list of candidate angles for the treatment stage based on the pretreatment images.

19. The radiation therapy apparatus of claim 14 , wherein the radiation therapy apparatus is a helical delivery radiation therapy apparatus, and wherein the treatment couch moves through the rotatable gantry as the rotatable gantry rotates.