Calibration Tool Alignment for Radiation Therapy Coordinate Systems
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Solution Overview
Problem
There is a need for improved methods and systems to accurately calibrate the alignment between the coordinate systems of imaging systems, such as CBCT systems, and stereotactic fixation units in radiation therapy, to prevent positioning errors during treatment due to manufacturing tolerances and angular variations.
Innovation Solution
A calibration method and system that uses a calibration tool with reference objects of known positions in the stereotactic coordinate system, capturing two-dimensional images to determine image coordinates, and calculating a transformation between the imaging system and stereotactic coordinate systems to account for translational and rotational differences, ensuring precise alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a CBCT system is used for imaging, then volumetric reconstruction of the treatment volume can be created, but angular variations between the CBCT coordinate system and the stereotactic fixation unit coordinate system cause positioning errors
Solution Approach 1:
A calibration tool with reference objects of known positions is introduced as an intermediary between the CBCT imaging system and the stereotactic fixation unit. The calibration tool serves as a common reference that allows accurate determination of the transformation between the two coordinate systems, eliminating positioning errors caused by angular variations.
2Adaptability or versatility
If the stereotactic fixation unit coordinate system and CBCT coordinate system are not aligned, then manufacturing tolerances cause angular variations, but calibration can correct these variations
Solution Approach 1:
Calibration is performed before treatment to pre-determine the transformation between coordinate systems. By conducting the calibration in advance using a known reference tool, the system establishes accurate transformation parameters that compensate for manufacturing tolerances and ensure reliable positioning during subsequent treatments.
3Measurement precision
If reference objects with known positions are used for calibration, then transformation between coordinate systems can be calculated, but multiple images and processing are required
Solution Approach 1:
The calibration tool with multiple reference objects serves multiple functions: it provides known positions for calculating transformation, enables verification of calibration accuracy, and can be used for both initial calibration and quality assurance. This multi-functionality justifies the procedural complexity by providing comprehensive calibration capabilities.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides a highly accurate calibration, reducing positioning errors and ensuring precise alignment between imaging and stereotactic systems, thereby improving the accuracy of radiation therapy treatments.
Implementation Method 1
irradiating a calibration tool comprising at least one reference object with ionizing radiation during an image scanning procedure using a radiation unit of the imaging system
Data Source
AI summary
A method of calibrating a positioning system in a radiation therapy system which includes a radiation therapy unit having a fixed radiation focus, includes irradiating a calibration tool having at least one reference object, capturing at least one two-dimensional image including cross-sectional representations of reference objects of the calibration tool and determining image coordinates of the representation of each reference object. Based on the reference objects' image coordinates, positions of the reference objects in the stereotactic coordinate system relative to an origin of the calibration tool and the position of the origin of the calibration tool relative to the imaging unit, a position difference between the position of the calibration tool in the stereotactic coordinate system and a position of the calibration tool in an imaging system coordinate system including a translational and rotational position difference is calculated.