Multi-leaf Collimator Drive Mechanism for Radiotherapy
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Solution Overview
Problem
Conventional multi-leaf collimator drive systems face issues with high friction, noise, production costs, assembly complexity, and servicing challenges due to the limitations of leadscrew and rack and pinion systems, particularly in accommodating a large number of leaves and maintaining radiation beam integrity.
Innovation Solution
A compact modular drive mechanism using a sub-frame to distribute motors and leadscrews efficiently, allowing for faster leaf movement and reduced component count, with a precision machined leadscrew and low-friction nut, and a drive coupling system that minimizes interference with the radiation beam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional leadscrew system is used to drive MLC leaves, then the leaves can be actuated, but high friction and noise are generated during operation
Solution Approach 1:
The patent replaces the conventional leadscrew mechanical transmission system with a direct-drive motor system. Each MLC leaf is driven by its own dedicated motor that couples directly to the leaf without intermediate mechanical elements like leadscrews. This eliminates the friction and noise problems inherent in leadscrew systems while maintaining reliable leaf actuation.
2Adaptability or versatility
If motors are mounted directly behind each leaf to enable individual actuation, then each leaf can be driven independently, but the motor arrangement becomes complex and interferes with the radiation beam
Solution Approach 1:
The patent relocates the motor mounting position from behind the leaves (one-dimensional arrangement) to the side of the leaf bank (two-dimensional arrangement). Motors are mounted on a motor plate positioned laterally adjacent to the leaf bank, allowing each motor to drive its corresponding leaf through a side-mounted drive mechanism. This spatial reconfiguration reduces complexity and avoids interference with the radiation beam path.
3Measurement precision
If a large number of leaves are accommodated in the MLC bank, then higher resolution treatment is achieved, but the drive system becomes more complex and difficult to service
Solution Approach 1:
The patent divides the drive system into modular units, with each motor and its associated drive mechanism forming an independent module. This segmentation allows individual motors to be accessed, removed, or replaced without affecting other parts of the system. The motor plate design enables easy access to all motors from the side, significantly simplifying servicing of large-leaf-count MLC systems.
4Ease of manufacture
If conventional motor mounting behind leaves is used, then drive coverage is complete, but production and assembly costs increase
Solution Approach 1:
The patent merges multiple motor mounting functions into a single integrated motor plate structure. All motors are mounted on this common plate that attaches to the side of the leaf bank, consolidating what would otherwise be multiple separate mounting structures. This merging reduces the total component count, simplifies assembly procedures, and lowers production costs while maintaining complete drive coverage for all leaves.
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
The solution reduces production and assembly costs, minimizes interference with the radiation beam, and improves servicing by allowing the drive system to be removed and reinstalled without affecting radiation performance, enabling better dynamic treatment therapies and higher leaf resolution.
Implementation Method 1
Each leaf is driven by an associated motor connected to the leaf via a drive means so as to extend or retract the leaf in its longitudinal direction, the drive means comprising a sub-frame on which at least a subset of the motors are mounted... and including a plurality of threaded drives disposed longitudinally, each being driven by a motor and being operatively connected to a leaf thereby to drive that leaf.
Data Source
AI summary
A multi-leaf collimator for a radiotherapy apparatus comprises at least one array of laterally-spaced elongate leaves, each leaf being driven by an associated motor connected to the leaf via a drive means so as to extend or retract the leaf in its longitudinal direction, the drive means comprising a sub-frame on which at least a subset of the motors are mounted, the sub-frame being mounted at a location spaced from the leaf array in a direction transverse to the lateral and longitudinal directions, and including a plurality of threaded drives disposed longitudinally, each being driven by a motor and being operatively connected to a leaf thereby to drive that leaf.