Tungsten Leaves: Leaf Speed Up to 3 cm/s, Density ≥ 18 g/cm³

Q: Why is tungsten used for MLC leaves?

Tungsten has a very high density (≈19.3 g/cm³) and high atomic number (74), making it extremely effective at attenuating high-energy X-rays used in radiotherapy, allowing for thinner leaves and sharper beam edges.

Q: How are tungsten leaves controlled?

Each leaf is controlled by an individual motor (servo or stepper) and drive mechanism, receiving positioning instructions from the treatment planning system via the MLC controller to dynamically shape the beam during treatment delivery.

Component Specifications

Definition

Tungsten leaves are individual, independently movable, high-density metal components arranged in banks within a multi-leaf collimator (MLC) system. They function as dynamic radiation attenuators that shape the therapeutic X-ray beam from a linear accelerator to match the tumor's contour in three dimensions, minimizing exposure to surrounding healthy tissues during radiotherapy.

Working Principle

Each tungsten leaf is driven by a precise motor (typically a servo or stepper motor) along a curved path to project a straight edge at the isocenter. The leaves move into and out of the radiation field based on digital treatment plans, creating custom apertures. Their high atomic number (74) and density (≈19.3 g/cm³) provide effective attenuation of megavoltage photons through photoelectric absorption and Compton scattering.

Materials

Primary: Tungsten or Tungsten alloy (e.g., W-Ni-Fe, W-Ni-Cu). May include minor alloying elements for machinability. Surface may have protective coatings. Backing structure often uses aluminum or composite materials for reduced weight.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Density	≥ 18 g/cm³
Leaf Speed	Up to 3 cm/s
Travel Range	Up to 200 mm from central axis
Maximum Field Size	Typically 40 cm x 40 cm
Positioning Accuracy	≤ 1 mm
Leakage Between Leaves	< 2%
Leaf Width At Isocenter	2.5 mm to 10 mm
Transmission Through Leaf	< 0.5%

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 13485, IEC 60601-2-1, IEC 60601-2-29

Parent Products

This component is used in the following industrial products

Multi-Leaf Collimator

A device used in radiation therapy to shape radiation beams to match tumor contours.

View Product Details

Multi-Leaf Collimator (MLC)

The Multi-Leaf Collimator (MLC) is a critical component of the Integrated Radiotherapy Treatment Planning and Delivery System.

View Product Details

Engineering Analysis

Risks & Mitigation

Mechanical wear or backlash affecting positional accuracy
Radiation leakage through leaf gaps
Motor or drive failure immobilizing a leaf
Thermal expansion causing positional drift
Software control errors leading to incorrect field shape

FMEA Triads

Trigger: Wear in drive mechanism or bearings
Failure: Reduced positioning accuracy or leaf sticking
Mitigation: Regular calibration and preventive maintenance; use of wear-resistant materials and lubrication where applicable.

Trigger: Control system software error or communication fault
Failure: Incorrect leaf position, creating wrong radiation field shape
Mitigation: Redundant position verification (e.g., potentiometers, encoders); independent safety interlocks; rigorous software testing and validation.

Trigger: Thermal effects from radiation absorption
Failure: Thermal expansion alters leaf position relative to isocenter
Mitigation: Thermal modeling in control algorithms; use of materials with low thermal expansion; active or passive cooling systems.

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Leaf position tolerance typically ±1 mm at isocenter, with tighter tolerances (e.g., ±0.5 mm) for high-precision systems. Must meet manufacturer specifications and regulatory requirements for medical devices.

Test Method

Regular quality assurance tests including: Picket Fence test for leaf positioning accuracy and reproducibility, Garden Fence test for inter-leaf leakage, transmission measurements using ion chambers, and Winston-Lutz test for isocenter coincidence. Performed per TG-142 (AAPM) and manufacturer guidelines.

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

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Inspection readiness

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Manufacturers of Tungsten Leaves

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Frequently Asked Questions

Why is tungsten used for MLC leaves?