Method of calibrating a patient monitoring system for use with a radiotherapy treatment apparatus

Patent metadata

Field	Value
Publication number	US-10861193-B2
Application number	US-201515516628-A
Country	US
Kind code	B2
Filing date	Sep 29, 2015
Priority date	Oct 2, 2014
Publication date	Dec 8, 2020
Grant date	Dec 8, 2020

Abstract

A calibration sheet is located at a first position where its surface substantially corresponds to the expected position of a patient surface lying on a mechanical couch during treatment. Images of the calibration sheet are obtained and processed to ascertain relative locations and orientations of the image detectors obtaining the images and optical distortion parameters indicative of optical distortions present in the obtained images of the calibration sheet. The calibration sheet is then re-located to a known position relative to the iso-centre of the treatment apparatus and images of the re-located calibration sheet are obtained and processed to determine a transform corresponding to the relocation of the calibration sheet from the first position to the iso-centre of the treatment apparatus. Data indicative of optical distortions present in the images and data indicative of the locations and orientations of the image detectors relative to the iso-centre of the treatment apparatus are stored.

First claim

The invention claimed is:

1. A method of calibrating a patient monitoring system including a plurality of image detectors arranged to view a surface of a patient lying on a mechanical couch of a radio therapy treatment apparatus, the method comprising:
identifying an iso-centre of the treatment apparatus;
performing a first calibration stage by:
locating a calibration object at a first position where a visible surface of the calibration object substantially corresponds to an expected position of the surface of the patient lying on the mechanical couch of the radio therapy treatment apparatus during treatment, the first position being above the previously identified iso-centre of the treatment apparatus to account for a difference between the expected position of the patient lying on the mechanical couch and the iso-centre of the treatment apparatus; and
obtaining images of the calibration object using the plurality of image detectors and processing the obtained images to ascertain relative locations and orientations of the plurality of image detectors and optical distortion parameters indicative of optical distortions present in the images of the calibration object obtained by the image detectors;

performing a second calibration stage by:
re-locating the calibration object to a second position at a known position relative to the iso-centre of the treatment apparatus; and
obtaining images of the re-located calibration object using the plurality of image detectors and processing the obtained images to determine a transform corresponding to the relocation of the calibration object from the first position to the iso-centre of the treatment apparatus; and

storing data indicative of optical distortions present in the images obtained by the image detectors of the calibration object in the first position during the first calibration stage, and data indicative of the locations and orientations of the image detectors relative to the iso-centre of the treatment apparatus determined by applying the determined transform obtained during the second calibration stage to the ascertained relative locations and orientations of the image detectors.

2. The method of claim 1 , wherein the patient monitoring system-includes a single stereoscopic camera having a plurality of image detectors.

3. The method of claim 1 , wherein the patient monitoring system includes a plurality of stereoscopic cameras each having a plurality of image detectors, wherein determining a transform corresponding to the relocation of the calibration object from the first position to the iso-centre of the treatment apparatus comprises:
individually processing images from each the plurality of stereoscopic cameras to determine for each of the stereoscopic cameras, a transform corresponding to the re-location of the calibration object from the first position to the iso-centre of the treatment apparatus; and
determining an average transform corresponding to the relocation of the calibration object from the first position to the iso-centre of the treatment apparatus.

4. The method of claim 1 , wherein the patient monitoring system includes a plurality of stereoscopic cameras each having a plurality of image detectors, wherein determining a transform corresponding to the relocation of the calibration object from the first position to the iso-centre of the treatment apparatus comprises:
processing images from one the plurality of stereoscopic cameras to determine a transform corresponding to the relocation of the calibration object from the first position to the iso-centre of the treatment apparatus.

5. The method of claim 1 , wherein at the first position the calibration object is located 5 to 10 cm above the identified location of iso-centre of the radio therapy treatment apparatus.

6. The method of claim 1 , wherein the patient monitoring system includes one or more lenses located between the patient and the image detector and, wherein determining lens distortion parameters indicative of optical distortions for each of the plurality of image detectors comprises:
applying transformations that account for perspective distortions arising from the relative locations and orientations of the image detectors causing the image detectors to view the surface of a calibration object at an oblique angle; and
comparing the transformed images to an expected image of the calibration object from a predefined viewpoint to identify optical distortions.

7. The method of claim 6 , wherein the calibration object includes a calibration sheet having markings located in a known pattern, wherein the step of comparing the transformed images to an expected image of the calibration object to identify optical distortions comprises:
processing the transformed images to identify locations of markings present on the calibration sheet and comparing with the positions of the markings in the expected image of the calibration sheet viewed from a predefined viewpoint.

8. A method of operating a patient monitoring system including a plurality of image detectors arranged to view the surface of a patient lying on a mechanical couch of a radio therapy treatment apparatus, the method comprising:
implementing a plurality of calibrations of the patient monitoring system, the calibrations being done by:
identifying an iso-centre of the treatment apparatus;
performing a first calibration stage by:
locating a calibration object at a first position where a visible surface of the calibration object substantially corresponds to an expected position of the surface of the patient lying on the mechanical couch of the radio therapy treatment apparatus during treatment, the first position being above the previously identified iso-centre of the treatment apparatus to account for a difference between the expected position of the patient lying on the mechanical couch and the iso-centre of the treatment apparatus; and
obtaining images of the calibration object using the plurality of image detectors and processing the obtained images to ascertain relative locations and orientations of the plurality of image detectors and optical distortion parameters indicative of optical distortions present in the images of the calibration object obtained by the image detectors;

performing a second calibration stage by:
re-locating the calibration object to a second position at a known position relative to the iso-centre of the treatment apparatus; and
obtaining images of the re-located calibration object using the plurality of image detectors and processing the obtained images to determine a transform corresponding to the relocation of the calibration object from the first position to the iso-centre of the treatment apparatus; and

storing data indicative of optical distortions present in the images obtained by the image detectors of the calibration object in the first position during the first calibration stage, and data indicative of the locations and orientations of the image detectors relative to the iso-centre of the treatment apparatus determined by applying the determined transform obtained during the second calibration stage to the ascertained relative locations and orientations of the image detectors,
wherein each of the plurality of calibrations is implemented with the calibration object located at a different first position, and the data stored as a result of each of the plurality of calibrations further comprises an indication of the location of the first position used for the calibration;
determining an actual position of a visible surface of the patient;
selecting the data stored as a result of the calibration for which the location of the first position used for the calibration corresponds to the actual position of the surface of the patient;

Assignees

• Vision Rt Ltd

Inventors

• Mead Edward
• Meir Ivan

Classifications

• G06T7/85 Primary

  Stereo camera calibration · CPC title

• A61N5/1049 Primary

  for verifying the position of the patient with respect to the radiation beam · CPC title

• G06T7/70

  Determining position or orientation of objects or cameras (camera calibration G06T7/80) · CPC title

• A61N2005/1059

  using cameras imaging the patient · CPC title

• H04N13/243

  using three or more two-dimensional [2D] image sensors · CPC title