Editing Isocentric technique

{{refimprove|date=February 2017}}
[[File:Linac radiotherapy.png|thumb|[[Linear particle accelerator|<span style="color:black;">Linac</span>]] movements: [[Gantry crane|<span style="color:red;">gantry</span>]] <span style="color:red;">rotation</span>, [[collimator|<span style="color:blue;">collimator</span>]] <span style="color:blue;">twist</span>, <span style="color:green;">bed swing</span>.]]
An '''isocentric technique''' is where all beams used in a [[radiation therapy|radiation treatment]] have a common focus point, a.k.a. the [[isocenter]]. Isocentric techniques require less patient repositioning as multiple field arrangements can be delivered with gantry and collimator movements, reducing treatment times.<ref>{{cite book|last1=Mayles|first1=P.|last2=Nahum|first2=A.|last3=Rosenwald|first3=J.C.|title=Handbook of radiotherapy physics|date=2007|publisher=Taylor & Francis|location=Boca Raton|isbn=9781420012026|page=692}}</ref> 

==Definition==
The idealized intersection point of the gantry axis of rotation with that of the [[collimator]] and treatment table is known as the mechanical isocenter<ref>{{cite book|last1=Greene|first1=David|last2=Peter C.|first2=Williams|title=Linear accelerators for radiation therapy|date=1997|publisher=CRC Press|location=New York|isbn=9780750304764|page=121|edition=2}}</ref>

In practice, due to the heavy weight and mechanical imperfections of the system, the isocenter is not a single point and its location changes with the rotation of the gantry, [[collimator]] or couch. This causes small uncertainties in the determination of isocenter position, typically less than 2 [[millimetres]]<ref>{{cite journal|last1=Klein|first1=Eric E.|last2=Hanley|first2=Joseph|last3=Bayouth|first3=John|author4-link=Fang-Fang Yin|last4=Yin|first4=Fang-Fang|last5=Simon|first5=William|last6=Dresser|first6=Sean|last7=Serago|first7=Christopher|last8=Aguirre|first8=Francisco|last9=Ma|first9=Lijun|last10=Arjomandy|first10=Bijan|last11=Liu|first11=Chihray|last12=Sandin|first12=Carlos|last13=Holmes|first13=Todd|title=Task Group 142 report: Quality assurance of medical acceleratorsa)|journal=Medical Physics|date=17 August 2009|volume=36|issue=9|pages=4197–4212|doi=10.1118/1.3190392|pmid=19810494|doi-access=free}}</ref>

==Working==
The movements of the [[linear particle accelerator]] (or linac) are threefold:
# the [[Gantry crane|gantry]] rotates (like a big crane arm)
# the [[collimator]] twists in the head of the gantry
# the bed swings around on the floor
<!-- Unsourced image removed: [[Image:Linac.jpg]] --><!-- Missing image removed: [[Image:Linac Collimatortwist.png]] -->
All of these movements in the modern linac occur around an axis that runs through the isocenter. In this way, if the centre of the target area in the patient's body is moved to coincide with the [[isocenter]], then all motions of the machine will remain centred on the target. This way, non-target areas will only receive short durations of [[radiation]], reducing damage to them, while the target area receives constant radiation.

==References==
{{Reflist}}
==Further reading==
*{{cite journal|last1=Rowshanfarzad|first1=P|last2=Sabet|first2=M|last3=O'Connor|first3=DJ|last4=Greer|first4=PB|title=Isocenter verification for linac-based stereotactic radiation therapy: review of principles and techniques.|journal=Journal of Applied Clinical Medical Physics|date=15 November 2011|volume=12|issue=4|pages=3645|doi=10.1120/jacmp.v12i4.3645|pmid=22089022|pmc=5718736}}

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[[Category:Medical treatments]]


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