Radiotherapy Dose Measurement Using Imaging-Guided Detector Alignment
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Solution Overview
Problem
Conventional methods for measuring radiotherapeutic dose distribution in MR-guided linear accelerators are inaccurate due to reliance on visual alignments and optical aids, which are limited by the small bore size and restricted visibility, leading to suboptimal alignment and measurement precision.
Innovation Solution
A method involving a shorter and wider water tank with a detector holder containing a radio-opaque marker and visual reference point, aligned using imaging apparatus to ensure precise positioning of the marker at the isocentre, allowing for accurate measurement of dose distribution in both vertical and horizontal directions, and a tank design with reduced wall thickness for minimized radiation attenuation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional visual alignment methods are used in MR linacs, then the alignment process is simple and quick, but the alignment accuracy and measurement precision are insufficient due to limited visibility and small bore size
Solution Approach 1:
The patent replaces conventional visual alignment methods with imaging-based alignment using the MR scanner. The imaging apparatus captures images of the water tank and detector holder, and processing circuitry automatically determines their positions and orientations, substituting manual visual alignment with automated image-based alignment to improve precision in the constrained MR linac environment
Solution Approach 2:
The patent introduces radio-opaque markers as intermediaries to facilitate alignment. These markers are attached to the water tank and detector holder, serving as visible references for the imaging apparatus to accurately determine positions and orientations without relying on direct visual alignment through the limited bore space
2Measurement precision
If a conventional water tank is used for dose distribution measurement, then the measurement process is straightforward, but the tank walls cause significant radiation attenuation leading to measurement errors
Solution Approach 1:
The patent applies local quality by making the water tank walls non-uniform in thickness. The front wall (facing the radiation source) is made thinner to minimize radiation attenuation, while the rear wall can be thicker for structural support. This localized variation in wall thickness optimizes radiation transmission for measurement accuracy while maintaining tank integrity
3Measurement precision
If the detector is positioned away from the water surface for measurements, then the measurement process is simple, but the depth measurements become inaccurate due to surface tension and meniscus effects
Solution Approach 1:
The patent replaces manual depth estimation methods with automated image-based depth measurement. The imaging apparatus captures images showing the detector holder position relative to the water surface, and processing circuitry automatically calculates the vertical distance, eliminating the need for manual measurement and avoiding errors from surface tension and meniscus effects
Solution Approach 2:
The patent uses radio-opaque markers attached to the detector holder as intermediaries for depth measurement. These markers are visible in the imaging apparatus, allowing automatic determination of the detector's vertical position relative to the water surface without direct contact or manual measurement
4Measurement precision
If extrapolation is used to determine dose distribution at depths beyond measurement range, then the measurement process is limited by tank size, but extrapolation introduces significant errors
Solution Approach 1:
The patent changes the physical parameters of the water tank by reducing wall thickness (especially the front wall) and optimizing the water volume. This allows the radiation beam to penetrate deeper into the water with minimal attenuation, enabling direct measurement at greater depths without relying on extrapolation, thereby improving dose distribution accuracy
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 enhances alignment accuracy and measurement precision, enabling more comprehensive dose distribution characterization with reduced extrapolation errors, even in constrained spaces like MR linacs, by using imaging to guide the placement of the detector holder and tank within the bore.
Implementation Method 1
rotating the gantry and monitoring the detector holder using the imaging apparatus to determine the position of the marker relative to the isocentre
Implementation Method 2
determine the radiation dose distribution within the patient's body, taking account of attenuation of the radiation beam as it passes through bodily tissue
Data Source
Figure 1A~1B
Figure 2
Figure 3A
AI summary
A method for the measurement of dose distribution in radiotherapy apparatus comprising an apparatus for generating a beam of therapeutic radiation and an imaging apparatus, one or both apparatuses being mounted to a rotatable gantry adapted in use to rotate around a bore of the radiotherapy apparatus and around an isocentre therein, the method comprising: placing a detector holder within a tank, the detector holder comprising a radio-opaque marker and a visual reference point, the marker and the reference point being separated and in a fixed spatial relationship to each other, and the tank in use containing a liquid having a surface level uppermost; locating the tank within the bore such that the detector holder is in the vicinity of the isocentre; rotating the gantry and monitoring the position of the detector holder using the imaging apparatus to determine the position of the marker relative to the isocentre; displacing the detector holder vertically such that the reference point is positioned at a point level with a desired surface level of the liquid, and adding liquid to or removing liquid from the tank until the surface of the liquid is at the same level as the reference point. Features of the detector holder and tank are also described.