Method and apparatus for real-time tumor tracking by detecting annihilation gamma rays from low activity position isotope fiducial markers

1. A method for real-time tracking of a target in a human body, the method comprising the acts of:

implanting into the target a plurality of physical positron emission fiducial markers having a low activity positron-emitting isotope source;

detecting two annihilation gamma rays resulting from positron annihilation associated with each of a plurality of position-emitting nuclear decay events of the low activity positron-emitting isotope source using a plurality of position-sensitive detectors, wherein the plurality of position-sensitive detectors comprises two pairs of position-sensitive detector modules mounted external to the human body in an orthogonal orientation such that the angle between the two pairs of position-sensitive detector modules is between 65 degrees and 90 degrees;

forming a coincident line from only the two detected annihilation gamma rays for each of the plurality of position-emitting nuclear decay events;

sorting the coincident lines into clusters based on an iterative Expectation-Maximization clustering algorithm;

determining the locations of the plurality of physical position emission fiducial markers using only said clusters; and

tracking, during radiation therapy delivery, movement and change of orientation of the target in real-time based on a change in position and orientation of plurality of physical positron emission fiducial markers, wherein said tracking provides target movement information for use in performing said radiation therapy delivery.

2. The method of claim 1 , wherein said tracking comprising tracking movement and change of orientation of the target in real-time without reconstructing a radioactive distribution image.

3. The method of claim 1 , further comprising:

gating off the plurality of position-sensitive detectors during therapy x-ray pulses, and

acquiring positron emission data from the plurality of physical positron emission fiducial markers between said therapy x-ray pulses.

4. The method of claim 1 , wherein tracking in real-time comprises tracking the movement and change of orientation of the target at a sampling rate of at least 10 samples per second.

5. The method of claim 1 , wherein tracking, during radiation therapy delivery, movement and change of orientation of the target in real-time based on a change in position and orientation of the plurality of physical positron emission fiducial markers, wherein said tracking provides target movement information for use in performing said radiation therapy delivery

6. The method of claim 1 , wherein identifying the location comprises identifying a location of the positron emission marker using each of said coincident line clusters with no more than a 100 ms delay.

7. The method of claim 1 , wherein said tracking further comprises tracking the target with sub-millimeter accuracy.

8. The method of claim 1 , wherein said low activity positron isotope is selected from the list consisting of: I-124, As-74, Rb-84, Na-22, Al-26, Ge-68, V-48 and Co-58.

9. The method of claim 1 , wherein implanting comprises one of implanting the positron emission marker in the target or attaching the positron emission marker to the target.

10. The method of claim 1 , wherein implanting comprises implanting a plurality of metallic positron emission fiducial markers having a low activity positron isotope into the target, wherein the plurality of metallic positron emission fiducial markers each comprise a radioactive core inside a metallic capsule.

11. A system for radiation therapy based on real-time three-dimensional position and orientation of a target in a human body, comprising:

a plurality of physical positron emission fiducial markers implanted into the target, the plurality of physical positron emission fiducial markers having a low activity positron-emitting isotope source;

a plurality of detectors arranged near a radiation isocenter configured to detect two annihilation gamma rays resulting from position annihilation associated with each of a plurality if positron-emitting nuclear decay events of the low activity positron-emitting isotope source of the plurality of physical positron emission fiducial markers, wherein the plurality of position-sensitive detectors comprises two pairs of position-sensitive detector modules mounted external to the human body in an orthogonal orientation such that the angle between the two pairs of position-sensitive detector modules is between 65 degrees and 90 degrees; and

a module configured to:

form a coincident line from only the two detected annihilation gamma rays for each of the plurality of position-emitting nuclear decay events,

sort the coincident lines into clusters based on an iterative Expectation-Maximization clustering algorithm,

determine the location of one of the plurality of physical position emission fiducial markers using only said clusters, and

track, during radiation therapy delivery, movement and change of orientation of the target in real-time based on a change in position and orientation of the plurality of physical positron emission fiducial markers, wherein said module provides target movement information for use in performing said radiation therapy delivery.

12. The system of claim 11 , wherein the module is configured to track movement and change of orientation of the target in real-time without reconstructing a radioactive distribution image.

13. The system of claim 11 , wherein the module is further configured to gate off the plurality of position-sensitive detectors during therapy x-ray pulses, and to acquire positron emission data from the plurality of physical positron emission fiducial markers between said therapy x-ray pulses.

14. The system of claim 11 , wherein the module is configured to track in real-time the movement and change of orientation of the target at a sampling rate of at least 10 samples per second.

15. The system of claim 11 , wherein the module is configured to track, during radiation therapy delivery, movement and change of orientation of the target in real-time based on a change in position and orientation of the plurality of physical positron emission fiducial markers, wherein the module is further to provide target movement information for use in performing said radiation therapy delivery.

16. The system of claim 11 , wherein the module is configured to identify the location of the positron emission marker using each of said coincident line clusters with no more than a 100 ms delay.

17. The system of claim 11 , wherein the module is configured to track the target with sub-millimeter accuracy.

18. The system of claim 11 , wherein said low activity positron isotope is selected from the list consisting of: I-124, As-74, Rb-84, Na-22, Al-26, Ge-68, V-48 and Co-58.

19. The system of claim 11 , wherein the plurality of physical positron emission fiducial markers are implanted in or attached to the target.

20. The system of claim 11 , wherein the plurality of physical positron emission fiducial markers comprise a radioactive core inside a metallic capsule.

21. The system of claim 20 , wherein the metallic capsule has an outside diameter of between 0.5 mm and 0.8 mm.