Methods for PET detector afterglow management

Patent metadata

Field	Value
Publication number	US-11287540-B2
Application number	US-202016887896-A
Country	US
Kind code	B2
Filing date	May 29, 2020
Priority date	Jul 11, 2017
Publication date	Mar 29, 2022
Grant date	Mar 29, 2022

Abstract

Disclosed herein are methods and devices for the acquisition of positron emission (or PET) data in the presence of ionizing radiation that causes afterglow of PET detectors. In one variation, the method comprises adjusting a coincidence trigger threshold of the PET detectors during a therapy session. In one variation, the method comprises adjusting a gain factor used in positron emission data acquisition (e.g., a gain factor used to multiply and/or shift the output(s) of a PET detector(s)) during a therapy session. In some variations, a method for acquiring positron emission data during a radiation therapy session comprises suspending communication between the PET detectors and a signal processor of a controller for a predetermined period of time after a radiation pulse has been emitted by the linac.

First claim

The invention claimed is:

1. A radiation therapy system comprising:
a therapeutic radiation source configured to output radiation by directing one or more radiation pulses toward a PET-avid region of interest, wherein each radiation pulse has a predetermined pulse duration;
a plurality of PET detectors configured to detect a positron annihilation emission path by detecting a pair of positron annihilation photons incident upon a portion of the detectors within a coincidence time-window and to generate a detector signal that exceeds a coincidence trigger threshold; and
a controller in communication with the plurality of PET detectors, wherein the controller is configured to adjust the coincidence trigger threshold during a therapy session in response to afterglow of the PET detectors caused by the one or more radiation pulses, wherein the coincidence trigger threshold is adjusted based on the radiation output of the therapeutic radiation source.

2. The system of claim 1 , wherein the controller is configured to adjust the coincidence trigger threshold after a threshold number of radiation pulses have been directed toward the region of interest.

3. The system of claim 2 , wherein the coincidence trigger threshold is from about two photon-triggers to about five photon-triggers.

4. The system of claim 3 , wherein the coincidence trigger threshold is a first coincidence trigger threshold and the threshold number of radiation pulses is a first threshold number of radiation pulses, and wherein the controller is configured to adjust the first coincidence trigger threshold to a second coincidence trigger threshold after a second threshold number of radiation pulses have been directed toward the region of interest.

5. The system of claim 4 , wherein the second coincidence trigger threshold is greater than the first coincidence trigger threshold and the second threshold number of radiation pulses is greater than the first threshold number of radiation pulses.

6. The system of claim 5 , wherein the second coincidence trigger threshold is from about four photon-triggers to about six photon-triggers, and the second threshold number of radiation pulses is about 2,000.

7. The system of claim 6 , wherein the second coincidence trigger threshold is less than the first coincidence trigger threshold and the second threshold number of radiation pulses is greater than the first threshold number of radiation pulses.

8. The system of claim 2 , wherein the controller is configured to adjust the coincidence trigger threshold at least partially based on a timing schedule of the radiation pulses.

9. The system of claim 1 , wherein the controller is configured to adjust the coincidence trigger threshold based on changes in timing greater than 10% from baseline.

10. The system of claim 1 , wherein the controller is configured to adjust the coincidence trigger threshold when a dark count rate of one or more of the plurality of PET detectors exceeds a threshold dark count rate.

11. The system of claim 10 , wherein the threshold dark count rate is from about 3 Mcps to about 10 Mcps.

12. The system of claim 1 , wherein the controller further comprises a current detector configured to measure a bias current of one or more of the plurality of PET detectors, and wherein the controller is configured to adjust the coincidence trigger threshold when the bias current exceeds a threshold bias current value.

13. The system of claim 12 , wherein the threshold bias current value is from about 0.1 mA to about 1 mA.

14. The system of claim 1 , wherein the controller is configured to adjust the coincidence trigger threshold when the amount of radiation emitted from the therapeutic radiation source exceeds a threshold radiation level.

15. The system of claim 14 , wherein the threshold radiation level is from about 0.1 cGy/min to about 1 cGy/min.

16. The system of claim 1 , wherein the controller further comprises a signal processor and a switch configured to selectively communicate a PET detector output signal to the signal processor, wherein the switch is configured to suspend communication of the PET detector output signal to the signal processor for a predetermined period of time following each radiation pulse, wherein a ratio of the predetermined period of time to the duration of each radiation pulse is between about 25:1 to about 100:1.

17. The system of claim 16 , wherein the controller is configured to suspend communication of the PET detector output signal to the signal processor for the duration of each radiation pulse and the predetermined period of time following each radiation pulse.

18. The system of claim 17 , wherein the controller is configured to suspend communication of the PET detector output signal to the signal processor based on a gate signal.

19. The system of claim 18 , wherein the gate signal causes the controller to suspend communication of the PET detector output signal to the signal processor for at least 100 μs following each radiation pulse.

20. A method for automatically adjusting the coincidence trigger threshold for PET detectors comprising:
measuring a characteristic of a radiation therapy system comprising two or more PET detectors having a coincidence trigger threshold;
determining whether the measured characteristic exceeds a pre-determined threshold for that characteristic; and
adjusting the coincidence trigger threshold based on the determination of whether the measured characteristic exceeds the threshold for that characteristic.

21. The method of claim 20 , wherein adjusting the coincidence trigger threshold comprises increasing the coincidence trigger threshold if the measured characteristic exceeds the pre-determined threshold for that characteristic or decreasing the coincidence trigger threshold if the measured characteristic is at or below the pre-determined threshold for that characteristic.

22. The method of 21 , wherein the measured characteristic is a dark count rate of the two or more PET detectors and the pre-determined threshold is a dark count rate threshold.

23. The method of 21 , wherein the measured characteristic is a bias current of the two or more PET detectors and the pre-determined threshold is a bias current threshold.

24. The method of 21 , wherein the radiation therapy system comprises a temperature sensor, and wherein the measured characteristic is temperature and the pre-determined threshold is a temperature threshold.

25. The method of 21 , wherein the radiation therapy system comprises a radiation source having a pulse counter, and wherein the measured characteristic is a pulse count measured from the pulse counter and the pre-determined threshold is a pulse count threshold.

26. The method of 21 , wherein the radiation therapy system comprises a radiation source and a collimator, wherein the radiation source and the collimator are configured to operate together with a pre-determined timing tolerance, and wherein the measured characteristic is the amount of deviation from the pre-determined timing tolerance and the pre-determined threshold is a timing deviation threshold.

27. A method for detecting positron annihilation emission paths, the method comprising:
outputting radiation by directing one or more therapeutic radiation beam pulses to a target region, wherein the target region is PET-avid;
detecting a first positron annihilation emission path defined by a first

Assignees

• Reflexion Medical Inc

Inventors

• Olcott Peter Demetri
• Bieniosek Matthew Francis
• Harper Brent

Classifications

• A61N2005/1092

  Details · CPC title

• A61N2005/1052

  using positron emission tomography [PET] single photon emission computer tomography [SPECT] imaging · CPC title

• A61N5/1077

  Beam delivery systems · CPC title

• A61N5/1045 Primary

  using a multi-leaf collimator, e.g. for intensity modulated radiation therapy or IMRT · CPC title

• G01T7/005

  calibration techniques (stabilization of spectrometer G01T1/40) · CPC title