Contoured Multi-Layer MLC Apertures for Small-Field SRS

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Solution Overview

Problem

Existing multi-layer MLCs face challenges in achieving adequate dose distribution for small field sizes required in stereotactic radiosurgery, particularly for pediatric patients with disproportionately larger cranial lesions, and conventional designs compromise radiation delivery efficiency and precision.

Innovation Solution

The development of a multi-layer MLC with contoured beam-blocking leaves that form small apertures when closed, allowing precise delivery of focused treatment beams for targets of varying sizes and shapes, while maintaining the advantages of multi-layer MLCs such as compactness and robust shielding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional multi-layer MLCs are used, then compactness and robust shielding are maintained, but adequate dose distribution for small field sizes required for SRS cannot be achieved

Engineering Contradiction:

Improvedose distribution precisionVSAvoidfield size adaptability

Core Design Contradiction:

Manufacturing precisionVSAdaptability or versatility

Solution Approach 1:

The MLC leaves are designed with different end portion configurations: some leaves have concave end surfaces to form small circular apertures for SRS, while other leaves maintain straight or angled end surfaces for standard radiotherapy. This local differentiation allows the same multi-layer MLC structure to achieve both small field SRS precision and standard field versatility.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The MLC system dynamically selects which leaves to close based on treatment requirements. For SRS, specific leaves with concave ends are closed to form small apertures, while for standard radiotherapy, different leaf combinations are used. This dynamic configuration allows adaptation between small field SRS and standard field treatments without physical reconfiguration.

Inventive Principle:

Principle #15Dynamics

2Area of stationary object

If SRS cones are mounted externally on linear accelerator, then installation space is reduced, but collision hazard with treatment couch or patient increases and treatment delivery efficiency is compromised

Engineering Contradiction:

Improveinstallation spaceVSAvoidtreatment delivery efficiency

Core Design Contradiction:

Area of stationary objectVSProductivity

Solution Approach 1:

The SRS aperture-forming capability is merged into the existing multi-layer MLC structure rather than using separate external cones. The MLC leaves themselves form the aperture when closed, eliminating the need for external SRS cones and their associated mounting space, while avoiding collision hazards and maintaining treatment efficiency.

Inventive Principle:

Principle #5Merging (Combining)

3Productivity

If multi-layer MLCs with larger leaf widths are used, then handling of larger field sizes is improved, but adequate dose distribution for small field sizes is compromised

Engineering Contradiction:

Improvelarge field handling speedVSAvoidsmall field dose distribution

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

Data Source

PatentEP4304710B1SRS contoured multi-layer multileaf collimator

Publication Date: 2025.11.26 VARIAN MEDICAL SYSTEMS INC

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Figure 2A~2D

AI summary

An apparatus includes a first multileaf collimator (130) comprising a plurality of pairs of beam-blocking leaves each comprising an end portion. The end portions of the beam-blocking leaves of one pair (132a-b) are contoured to allow forming a first aperture (134) when the beam-blocking leaves of the pair are closed. The first aperture has a closed shape such as a circle in a beam's eye view.