Beam-off motion thresholds in radiation therapy based on breath-hold level determination

1. A computer-implemented method of performing a treatment fraction of radiation therapy, the method comprising:

determining a current position of a target volume of patient anatomy;

based on the current position of the target volume, computing an accumulated dose for tissue disposed within the target volume;

determining that the accumulated dose is less than a current dose budget of the tissue; and

in response to the accumulated dose being less than the current dose budget, applying a treatment beam to the target volume while the target volume is in the current position.

2. The computer-implemented method of claim 1 , wherein the current position is at least partially outside a planned treatment location for the target volume.

3. The computer-implemented method of claim 1 , further comprising generating a new value for the dose budget by subtracting the accumulated dose from the current dose budget.

4. The computer-implemented method of claim 3 , further comprising, based on the new value of the dose budget, modifying a beam-off threshold position for the target volume.

5. The computer-implemented method of claim 4 , wherein modifying the beam-off threshold position for the target volume comprises associating the beam-off threshold position with a first range of target positions and disassociating the beam-off threshold position from a second range of target positions, wherein the first range of target positions is closer to a planned treatment location for the target volume than the second range of target positions.

6. The computer-implemented method of claim 1 , further comprising, prior to applying the treatment beam to the target volume, determining that the current position is within a range of beam-off threshold positions for the target volume.

7. The computer-implemented method of claim 6 , further comprising, when a detected position of the target volume is outside the range of beam-off threshold positions, blocking application of the treatment beam for a portion of the treatment fraction.

8. The computer-implemented method of claim 1 , further comprising:

determining an equivalent breath-hold level based on the current position of the target volume; and

computing the accumulated dose based on the equivalent breath-hold level.

9. The computer-implemented method of claim 8 , wherein the equivalent breath-hold level is associated with a specific accumulated dose.

10. The computer-implemented method of claim 1 , further comprising:

determining a treatment beam intensity that is applied to the target volume while the target volume is in the current position; and

computing the accumulated dose based on the treatment beam intensity.

11. The computer-implemented method of claim 1 , wherein determining the current position of the target volume comprises measuring an external motion signal.

12. The computer-implemented method of claim 1 , wherein determining the current position of the target volume further comprises performing X-ray imaging of the target volume.

13. The computer-implemented method of claim 1 , further comprising based on the current position of the target volume, computing an accumulated dose for the tissue.

14. A system for performing a treatment fraction of radiation therapy, the system comprising:

an X-ray imaging device;

a treatment-delivering X-ray source configured to direct treatment X-rays to a target volume of patient anatomy;

an imaging X-ray source configured to direct imaging X-rays through the target volume and toward the X-ray imager; and

a processor configured to:

determine a current position of the target volume;

based on the current position of the target volume, compute an accumulated dose for tissue disposed within the target volume;

determine that the accumulated dose is less than a current dose budget of the tissue; and

in response to the accumulated dose being less than the current dose budget, cause the treatment-delivering X-ray source to apply a treatment beam to the target volume while the target volume is in the current position.

15. The system of claim 14 , wherein the current position is at least partially outside a planned treatment location for the target volume.

16. The system of claim 14 , wherein determining the current position of the target volume further comprises performing X-ray imaging of the target volume with the X-ray imaging device and the imaging X-ray source.

17. The system of claim 14 , wherein causing the treatment-delivering X-ray source to apply the treatment beam to the target volume while the target volume is in the current position comprises a portion of the treatment fraction.

18. A computer-implemented method of performing a treatment fraction of radiation therapy, the method comprising:

determining a current position of a target volume of patient anatomy;

based on the current position of the target volume, computing an accumulated dose for tissue associated with the target volume;

determining that the accumulated dose is greater than a current dose budget of the tissue; and

in response to the accumulated dose being greater than the current dose budget:

determining a remaining dose budget for the tissue associated with the target volume; and

based on the remaining dose budget for the tissue, modifying a beam-off threshold position for the target volume.

19. The computer-implemented method of claim 18 , wherein the tissue associated with the target volume comprises one of tissue disposed within the target volume or non-target tissue proximate the target volume.

20. The computer-implemented method of claim 19 , further comprising:

determining a new position of the target volume;

based on the new position of the target volume, computing a new accumulated dose for the tissue;

determining that the new accumulated dose is less than the remaining dose budget for the tissue; and

in response to the accumulated dose being less than the current dose budget, applying a treatment beam to the target volume while the target volume is in the new position.