Multi-Leaf Collimator Beam Shaping Using Projected Leaf Width
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Solution Overview
Problem
Current methods for determining the shape of a radiotherapy beam at a target position using a multi-leaf collimator are inadequate, particularly in accurately defining the beam shape due to assumptions about leaf width and alignment, leading to errors in beam edge positioning and radiation distribution.
Innovation Solution
A method that determines the projected width of each leaf in a multi-leaf collimator, taking into account the convergence of leaf planes laterally from the radiation source, allowing for a more accurate determination of the radiation beam shape at the target position by using the projected leaf width to adjust the beam shape dynamically during treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the projected width of leaves is assumed to be equal to their physical thickness, then the calculation is simple, but the beam edge positioning accuracy deteriorates
Solution Approach 1:
The patent changes the parameter used for leaf width from physical thickness to projected width. The projected width is calculated based on the leaf's distance from the beam axis and the geometry of the converging leaf planes, transforming a simple constant parameter into a variable parameter that depends on position, thereby improving accuracy without excessive complexity
Solution Approach 2:
The patent introduces a new dimensional consideration by accounting for the lateral displacement of the convergence point from the radiation source. This creates a geometric relationship where projected width varies with leaf position, adding a spatial dimension to the width calculation that resolves the accuracy problem
2Device complexity
If all leaves are assumed to have the same width, then the model is simplified, but the beam shape determination accuracy deteriorates at larger distances from the beam axis
Solution Approach 1:
The patent applies local quality by making the leaf width parameter location-dependent. Leaves closer to the beam axis use one projected width calculation, while leaves further away use a different calculation that accounts for the increased lateral displacement, allowing each region of the collimator to be modeled with appropriate precision
Solution Approach 2:
The patent transforms the uniform leaf width parameter into a position-varying parameter. The projected width for each leaf is calculated based on its specific distance from the beam axis and the convergence geometry, allowing the model to capture local variations in beam shaping accuracy
3Device complexity
If the convergence point is assumed to be at the radiation source, then the geometry is simplified, but the projected width calculation accuracy deteriorates
Solution Approach 1:
The patent performs preliminary geometric analysis to determine the actual convergence point location relative to the radiation source. This pre-calculated geometric relationship is then used in the projected width calculations, allowing the system to account for the displaced convergence point without requiring complex real-time calculations during treatment
Data Source
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AI summary
A method of determining the shape of a radiation beam of a radiotherapy system at a treatment position, the system comprising: a radiation source for projecting the radiation beam towards the treatment position; and a multi-leaf collimator disposed between the radiation source and the treatment position, the multi-leaf collimator comprising an array of moveable leaves that may be positioned to intersect and block parts of the radiation beam so as to define the shape of the radiation beam at the treatment position, wherein the leaves of at least one group in the array are aligned such that the planes of the leaves in that group converge at a point that is displaced laterally from the radiation source; the method comprising: for each leaf in the array that is positioned to intersect the radiation beam, determining a projected width with respect to the radiation beam, wherein the projected width is greater than the thickness of the respective leaf; and using the projected leaf width to determine the shape of the radiation beam at the treatment position.