Alternating Trapezoidal Leaf Geometry for Multileaf Collimator Leakage
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Solution Overview
Problem
Multileaf collimators (MLCs) face issues with interleaf leakage, which is unpredictable and can lead to radiation leakage and undesirable underdose effects, especially when the MLC rotates, and existing solutions like the 'tongue in groove' design are costly and may cause variations in penumbra and resolution.
Innovation Solution
The use of an alternating trapezoidal leaf geometry design in MLCs, where beam-blocking leaves with wider and narrower ends are arranged to converge at specific points offset from the radiation source, reducing interleaf leakage and maintaining uniform penumbra across the treatment field, while also reducing manufacturing costs by allowing identical construction of support structures for both banks of leaves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a 'tongue in groove' design is used to reduce interleaf leakage, then radiation leakage is reduced, but manufacturing cost increases significantly
Solution Approach 1:
The patent applies asymmetry by designing leaves with different geometries in opposing banks - one bank has leaves with a first geometry while the opposing bank has leaves with a second geometry. This asymmetric configuration reduces interleaf leakage through geometric interlocking without requiring expensive tongue-in-groove features on all leaves, thereby lowering manufacturing costs while maintaining radiation leakage reduction.
2Object-affected harmful factors
If a 'tongue in groove' design is used to reduce interleaf leakage, then radiation leakage is reduced, but underdose effects occur when treatment fields are combined
Solution Approach 1:
The asymmetric leaf geometry design creates complementary shapes between opposing banks that reduce interleaf leakage while maintaining more uniform penumbra characteristics. This allows for more accurate dose delivery when multiple treatment fields are combined, avoiding the underdose effects associated with tongue-in-groove designs.
3Object-affected harmful factors
If an asymmetrical shift of beam-blocking leaves is used to avoid gaps, then interleaf leakage is reduced, but penumbra and resolution vary across the treatment field
Solution Approach 1:
The patent uses asymmetry in leaf geometry rather than asymmetrical positioning. By designing leaves with specific geometric shapes that are asymmetric in form but symmetric in their effect on the beam, the system reduces interleaf leakage while maintaining uniform penumbra and resolution across the entire treatment field.
Solution Approach 2:
The patent applies local quality by designing different geometric characteristics for different regions of the leaves. The leaf geometries are optimized locally to achieve uniform penumbra across the field while maintaining the asymmetry needed to reduce interleaf leakage at specific locations.
Data Source
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AI summary
A multileaf collimator includes a plurality of beam-blocking leaves of a first type and a plurality of beam-blocking leaves of a second type. The beam-blocking leaves of the first type are alternatingly arranged with the beam-blocking leaves of the second type side by side. Each of the beam-blocking leaves of the first type has a trapezoidal geometry viewed in the leaf longitudinal moving direction comprising a wider end and a narrower end with the wider end being proximal to a source. Each of the beam-blocking leaves of the second type has a trapezoidal geometry viewed in the leaf longitudinal moving direction comprising a wider end and a narrower end with the wider end being distal to the source.