A tungsten alloy multi-leaf collimator has been in routine clinical use for both conventional and conformal radiotherapy for many years. And there are many pieces of medical shields in tungsten alloy multi-leaf collimator. They are tungsten alloy leaves. According to a report, the collimator comprised of 80 tungsten alloy leaves and two orthogonal pairs of back-up collimators is used to replace the conventional treatment head of a linear accelerator.
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It has been reported that each tungsten alloy leaf projects a width of 1 cm in the isocentric plane, allowing shaped photon treatment beams of up to 40 cm square. Radiation attenuation by the collimator components has been measured and substantially exceeds those requirements. The irregular portion of a field (shielded by the leaves only) receives, on average, a dose of less than 2% of the tumor dose. The effect on the penumbra of using leaves which translate linearly and have curved faces has been assessed and found not to degrade the sharpness of the beam fall-off significantly. The reproducibility of the video system used in positioning the leaves has been measured and gave a root mean square deviation of less than 0.3 mm in repeat setting of a 10 cm square field, and an accuracy always within 1 mm. The rationale for clinical use of the device is discussed and its effect on treatment quality control and reliability, is considered. All in all, tungsten alloy leaves – the medical shields in tungsten alloy multi-leaf collimator have good radiation attenuation for clinical use.
