Time-resolved pre-treatment portal dosimetry systems, devices, and methods

• US 9,089,696 B2
• Filed: 11/07/2013
• Issued: 07/28/2015
• Est. Priority Date: 11/07/2013
• Status: Active Grant

• Current Assignee: Siemens Healthineers International AG
• Original Assignee: Varian Medical Systems International AG (Siemens AG)
• Inventors: Podesta, Mark, Baltes, Christof, Verhaegen, Frans, Nijsten, Sebastiaan M. J. J. G., Persoon, Lucas C. G. G., Scheib, Stefan G.
• Primary Examiner(s): NGUYEN, KIET TUAN
• Application Number:
  US14/074,144
• Publication Number:
  US 20150124930A1
• Time in Patent Office: 628 Days
• Field of Search: 378/65, 378/62, 382/132
• US Class Current: 1/1
• CPC Class Codes: A61N 2005/1054 using a portal imaging system
• CPC Class Codes: A61N 5/1031 using a specific method of dose optimization
• CPC Class Codes: A61N 5/1047 with movement of the radiation head during application of radiation, e.g. for intensity modulated arc therapy or IMAT
• CPC Class Codes: A61N 5/1071 for verifying the dose delivered by the treatment plan
• CPC Class Codes: A61N 5/1075 for testing, calibrating, or quality assurance of the radiation treatment apparatus

Abstract

Systems, devices, and methods for pre-treatment verification of radiation dose delivery in arc-based radiation therapy devices using a time-dependent gamma evaluation method.

Claims

1. A time-dependent pre-treatment dosimetric evaluation method for a radiation therapy device, comprising:

generating a sequence of portal dose images based on images continuously acquired during beam delivery according to a treatment plan, each portal dose image in the sequence corresponding to a measured dose delivered at a predetermined time interval of the treatment plan;

for each predetermined time interval, comparing the generated portal dose image with a corresponding predicted portal dose image; and

evaluating dose delivery based on the comparison.

2. The method of claim 1, wherein each time interval corresponds to a respective control point (CP) of the treatment plan.

3. The method of claim 1, wherein the portal dose images are obtained using an electronic portal dose imaging device (EPID) calibrated for measuring absolute dose.

4. The method of claim 3, wherein the measured dose is an absolute dose.

5. The method of claim 3, wherein the absolute dose calibration includes an absolute (EPID) conversion model.

6. The method of claim 1, wherein the comparing includes using a time-dependent gamma evaluation method.

7. The method of claim 6, wherein the comparing comprises using the time-dependent gamma evaluation method to calculate one of, or in combination, dose differences, spatial differences, and time differences between points in the measured portal dose images and corresponding points in the predicted portal dose images as parameters.

8. The method of claim 7, further including storing the predicted portal dose images as a first data set mapped as a first 4D array including positional information and time information of the points in the predicted portal dose images, and storing the measured portal dose images as a second data set mapped as a second 4D array including positional information and time information of the points in the measured portal dose images.

9. The method of claim 8, wherein the positional information includes spatial locations of the predicted and measured radiation fields, and the time information includes the times of the predicted and measured radiation fields.

10. The method of claim 9, wherein the comparing includes comparing the first and second data sets using the time-dependent gamma evaluation method.

11. The method of claim 10, wherein the comparing includes computing a time-dependent gamma error matrix based on a gamma error function:

12. The method of claim 11, further comprising calculating the positional metric values for each point in the first and second data sets and the time metric values for each point in the first and second data sets by comparing the positional differences between corresponding points in the first and second data sets and the time differences between corresponding points in the first and second data sets.

13. The method of claim 11, wherein the quantity of interest includes radiation dose.

14. The method of claim 13, further including determining dose delivery errors based on the comparison.

15. A method for verifying quantities of interest of a radiation beam in an arc-based radiation therapy device, comprising:

continuously acquiring portal images during a continuous arc beam delivery using an electronic portal imaging device (EPID);

converting the acquired portal images into absolute portal dose images using a dosimetric calibration model;

resampling the absolute portal dose images into respective time divisions corresponding to a treatment plan'"'"'s control points (CPs) to obtain a sequence of measured portal dose images, each measured portal dose image in the sequence corresponding to a respective control point (CP);

comparing each of the measured portal dose images in the sequence with corresponding predicted portal dose images using a 4D time-dependent gamma evaluation function; and

determining dose delivery errors based on the comparison by assessing the amount of voxels that change over time with a gamma metric exceeding unity.

16. The method of claim 15, wherein the absolute dose calibration model includes an absolute EPID conversion model.

17. The method of claim 16, wherein the comparing comprises using the time-dependent gamma evaluation method to calculate one of, or in combination, dose differences, spatial differences, and time differences between points in the measured portal dose images and corresponding points in the predicted portal dose images as parameters.

18. The method of claim 17, further including storing the predicted portal dose images as a first data set mapped as a first 4D array including positional information and time information of the points in the predicted portal dose images, and storing the measured portal dose images as a second data set mapped as a second 4D array including positional information and time information of the points in the measured portal dose images.

19. The method of claim 18, wherein the positional information includes spatial locations of the predicted and measured radiation fields, and the time information includes the times of the predicted and measured radiation fields.

20. The method of claim 19, wherein the comparing includes comparing the first and second data sets using the time-dependent gamma evaluation method.

21. The method of claim 20, wherein the comparing includes computing a time-dependent gamma error matrix based on a gamma error function:

22. The method of claim 21, further comprising calculating the positional metric values for each point in the first and second data sets and the time metric values for each point in the first and second data sets by comparing the positional differences between corresponding points in the first and second data sets and the time differences between corresponding points in the first and second data sets.

23. The method of claim 21, wherein the quantity of interest includes radiation dose.

24. A system for verifying quantities of interest of a radiation beam in an arc-based radiation therapy device including a gantry, comprising:

a portal imaging device configured to measure incident radiation dose from predetermined radiation fields corresponding to an arc segment of the gantry and to generate a series of two-dimensional (2D) absolute portal dose images using a calibration model; and

a processing device operably connected to the portal dose imaging device and configured to store the series of 2D absolute portal dose images in a first 4D array having spatial locations and time of delivery of the predetermined radiation fields as dimensions, the processing device being further configured to store a series of predicted 2D portal dose images in a second 4D array having spatial locations and time of delivery of predicted radiation fields as dimensions;

wherein the processing device is further configured to compare points in the first 4D array with corresponding points in the second 4D array using a 4D gamma evaluation method, the gamma evaluation method including dose differences, spatial differences, and time differences between corresponding points in the first and second 4D arrays as parameters, and

wherein errors in the quantities of interest are determined based on the comparison.

25. The system of claim 24, wherein the arc-field radiation therapy device is one of an intensity modulated radiation therapy device and a volumetric modulated arc therapy device.

26. The system of claim 24, wherein the portal imaging device is an electronic portal imaging device (EPID).

27. The system of claim 26, wherein the processing device is further configured to generate a 4D gamma error matrix based on a gamma error function:

28. The system of claim 27, wherein the quantity of interest is radiation dose.

29. A non-transitory computer-readable storage medium upon which is embodied a sequence of programmed instructions for verifying quantities of interest of a radiation beam in a system including an arc-based radiation therapy device including a gantry and a computer processing system which executes the sequence of programmed instructions embodied on the computer-readable storage medium to cause the computer processing system to perform the steps of:

continuously acquiring portal images during a continuous arc beam delivery using an electronic portal imaging device (EPID);

converting the acquired portal images into absolute portal dose images using a dosimetric calibration model;

resampling the absolute portal dose images into respective time divisions corresponding to a treatment plan'"'"'s control points (CPs) to obtain a sequence of measured portal dose images, each measured portal dose image in the sequence corresponding to a respective control point (CP);

comparing each of the measured portal dose images in the sequence with corresponding predicted portal dose images using a time-dependent gamma evaluation function; and

determine dose delivery errors based on the comparison by assessing the amount of voxels that change over time exceeding unity.

30. The non-transitory computer-readable medium of claim 29, wherein the absolute dose calibration model includes an absolute EPID conversion model.

31. The non-transitory computer-readable medium of claim 30, wherein the comparing comprises using the time-dependent gamma evaluation method to calculate one of, or in combination, dose differences, spatial differences, and time differences between points in the measured portal dose images and corresponding points in the predicted portal dose images as parameters.

32. The non-transitory computer-readable medium of claim 31, further including storing the predicted portal dose images as a first data set mapped as a first 4D array including positional information and time information of the points in the predicted portal dose images, and storing the measured portal dose images as a second data set mapped as a second 4D array including positional information and time information of the points in the measured portal dose images.

33. The non-transitory computer-readable medium of claim 32, wherein the positional information includes spatial locations of the predicted and measured radiation fields, and the time information includes the times of the predicted and measured radiation fields.

34. The non-transitory computer-readable medium of claim 33, wherein the comparing includes comparing the first and second data sets using the time-dependent gamma evaluation method.

35. The non-transitory computer-readable medium of claim 34, wherein the comparing includes computing a time-dependent gamma error matrix based on a gamma error function:

36. The non-transitory computer-readable medium of claim 35, further comprising calculating the positional metric values for each point in the first and second data sets and the time metric values for each point in the first and second data sets by comparing the positional differences between corresponding points in the first and second data sets and the time differences between corresponding points in the first and second data sets.