Multileaf collimator: Difference between revisions

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[[File:MLCShape.svg|thumb|''MLC shape of an X-MLCs'']]

A '''multileaf collimator''' (also known as an '''MLC''') is device used in [[radiotherapy]] for defining the shape of a treatment field.

A '''multileaf collimator''' ('''MLC''') is a [[collimator]] or beam-limiting device that is made of individual "leaves" of a high [[atomic number]]ed material, usually [[tungsten]], that can move independently in and out of the path of a [[external beam radiotherapy|radiotherapy beam]] in order to shape it and vary its intensity.

[[Image:NeutronPort.gif|thumb|right|Simulation of a treatment neutron field collimated using MLC. The white bars represent MLC leaves]]

The goal of [[external beam radiotherapy]] is to deliver a target [[radiation dose|dose]] to the [[tumour]] while sparing dose to healthy tissue as much as possible. In order to achieve this goal, the radiation beam must be shaped to match the shape of the tumor from the [[beam's eye view]]. As it takes about 10cm of lead or tungsten to block radiation, this shaping is not easy to do automatically. The multileaf collimator was designed to do precisely that. A standard MLC consists of 40 or more pairs of tungsten plates called "leaves". Each leave can move independently in towards in centre of the treatment field, creating an approximation of any desired shape.

MLCs are used in external beam radiotherapy to provide conformal shaping of beams. Specifically, [[Radiation therapy#External beam radiation therapy|conformal radiotherapy]] and [[Intensity Modulated Radiation Therapy]] (IMRT) can be delivered using MLCs.

The MLC has improved rapidly since its inception and the first use of leaves to shape structures in 1965 <ref>{{cite journal | last=Takahashi | first=S | title=Conformation radiotherapy. Rotation techniques as applied to radiography and radiotherapy of cancer. | journal=Acta Radiologica: Diagnosis | year=1965 | issn=0567-8056 | pmid=5879987 | page=Suppl 242:1+}}</ref> to modern day operation and use. MLCs are now widely used and have become an integral part of any radiotherapy department. MLCs were primarily used for conformal radiotherapy, and have allowed the cost-effective implementation of conformal treatment with significant time saving,<ref>{{cite journal | last1=Brewster | first1=Linda | last2=Mohan | first2=Radhe | last3=Mageras | first3=Gig | last4=Burman | first4=Chandra | last5=Leibel | first5=Steven | last6=Fuks | first6=Zvi | title=Three dimensional conformal treatment planning with multileaf collimators | journal=International Journal of Radiation Oncology, Biology, Physics | publisher=Elsevier BV | volume=33 | issue=5 | date=1995-12-01 | issn=0360-3016 | pmid=7493834 | doi=10.1016/0360-3016(95)02061-6 | pages=1081–1089}}</ref> and also have been adapted for use for IMRT treatments. For conformal radiotherapy the MLC allows conformal shaping of the beam to match the borders of the target tumour. For intensity modulated treatments the leaves of a MLC can be moved across the field to create IMRT distributions (MLCs really provide a [[fluence]] modulation rather than intensity modulation).

The MLC was later discovered to be ideal for [[intensity-modulated radiotherapy]] (IMRT). IMRT involves optimising the precise amount of radiation that should be applied to each part of the beam in order to deliver an ideal treatment. By layering multiple MLC deliveries with different shapes atop one another, an approximation of this ideal treatment can be achieved.

[[File:Collimatore multilama.jpg|thumb|Leaves, changing shape, direct the beam to the right [[cancer]] area]]

[[Category:Radiobiology]]

The MLC is an important tool for radiation therapy dose delivery. It was originally used as a surrogate for alloy block field shaping and is now widely used for IMRT. As with any tool used in radiotherapy the MLC must undergo commissioning and quality assurance. Additional commissioning measurements are completed to model a MLC for [[treatment planning]]. Various MLCs are provided by different vendors and they all have unique design features as determined by specifications of design,<ref>{{cite journal | last1=Galvin | first1=James M. | last2=Smith | first2=Alfred R. | last3=Lally | first3=Brian | title=Characterization of a multileaf collimator system | journal=International Journal of Radiation Oncology, Biology, Physics | publisher=Elsevier BV | volume=25 | issue=2 | date=1993-01-15 | issn=0360-3016 | pmid=8420867 | doi=10.1016/0360-3016(93)90339-w | pages=181–192}}</ref> and these differences are quite significant.

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==References==

{{Reflist}}

[[Category:Medical equipment]]

[[Category:RadiobiologyMedical physics]]

[[Category:Particle accelerators]]

[[Category:Radiation therapy]]

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