Editing Isocentric technique (section)

==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>