Editing Monitor unit

A '''monitor unit''' ('''MU''') is a measure of machine output from a clinical accelerator for [[radiation therapy]] such as a [[linear accelerator]] or an [[orthovoltage]] unit. Monitor units are measured by monitor chambers, which are [[ionization chamber]]s that measure the [[radiation dose|dose]] delivered by a beam and are built into the treatment head of radiotherapy linear accelerators.<ref>{{cite book|last1=Halperin|first1=Edward C.|last2=Perez|first2=Carlos A.|last3=Brady|first3=Luther W.|title=Perez and Brady's principles and practice of radiation oncology|date=2008|publisher=Lippincott Williams & Wilkins|location=Philadelphia|isbn=9780781763691|page=152|edition=5th}}</ref>

==Calibration and dose quantities==

Linear accelerators are calibrated to give a particular [[absorbed dose]] under particular conditions, although the definition and measurement configuration may vary among medical clinics.<ref>{{cite journal|last1=Lillicrap|first1=S C|last2=Owen|first2=B|last3=Williams|first3=J R|last4=Williams|first4=P C|title=Code of Practice for high-energy photon therapy dosimetry based on the NPL absorbed dose calibration service|journal=Physics in Medicine and Biology|date=1 October 1990|volume=35|issue=10|pages=1355–1360|doi=10.1088/0031-9155/35/10/301|bibcode=1990PMB....35.1355L }}</ref><ref>{{cite journal|last1=Nath|first1=Ravinder|last2=Biggs|first2=Peter J.|last3=Bova|first3=Frank J.|last4=Ling|first4=C. Clifton|last5=Purdy|first5=James A.|last6=van de Geijn|first6=Jan|last7=Weinhous|first7=Martin S.|title=AAPM code of practice for radiotherapy accelerators: Report of AAPM Radiation Therapy Task Group No. 45|journal=Medical Physics|date=July 1994|volume=21|issue=7|pages=1093–1121|doi=10.1118/1.597398|pmid=7968843|bibcode=1994MedPh..21.1093N |url=http://www.aapm.org/pubs/reports/rpt_47.PDF}}</ref>

The most common definitions are:<ref>{{cite book |last1=Mayles |first1=Philip |last2=Nahum |first2=Alan |last3=Rosenwald |first3=Jean-Claude |year=2007 |title=Handbook of Radiotherapy Physics - Theory and Practice |chapter=Chapter 20: From Measurements to Calculations |publisher=Taylor & Francis |isbn=978-0-7503-0860-1}}</ref>

# The monitor chamber reads 100&nbsp;MU when an [[absorbed dose]] of 1 [[Gray (unit)|gray]] (100 [[rad (unit)|rads]]) is delivered to a point at the depth of maximum dose in a water-equivalent [[Imaging phantom|phantom]] whose surface is at the [[isocenter]] of the machine (i.e. usually at 100&nbsp;cm from the source) with a field size at the surface of 10&nbsp;cm&nbsp;×&nbsp;10&nbsp;cm.
# The monitor chamber reads 100&nbsp;MU when an absorbed dose of {{convert|1|Gy|rad|abbr=on}} is delivered  to a point at a given depth in the phantom with the surface of the phantom positioned so that the specified point is at the isocentre of the machine and the field size is 10&nbsp;cm&nbsp;×&nbsp;10&nbsp;cm at the isocentre.

Some linear accelerators are calibrated using source-to-axis distance (SAD) instead of source-to-surface distance (SSD), and calibration (monitor unit definition) may vary depending on hospital custom.

Early radiotherapy was performed using "constant SSD" treatments, and so the definition of monitor unit was adopted to reflect this calibration geometry.

Modern radiotherapy is performed using [[isocentric technique|isocentric]] treatment [[treatment planning|plans]], so newer definitions of the monitor unit are based on geometry at the [[isocenter]] based on the source-to-axis distance (SAD).

==Secondary monitor unit calculations ==

Nearly 60% of the reported errors involved a lack of an appropriate independent secondary check of the treatment plan or dose calculation <ref>ed. International Atomic Energy Agency., "[https://www.iaea.org/publications/6974/commissioning-and-quality-assurance-of-computerized-planning-systems-for-radiation-treatment-of-cancer Commissioning and Quality Assurance of Computerized Planning Systems for Radiation Treatment of Cancer]"</ref>

With the development and technological advances, radiotherapy requires that high doses of radiation are delivered to the tumor with increasing precision. According to the recommendations of the International Commission on Radiation Units and Measurements (ICRU) in Publication 24 
,<ref>{{Cite journal|url=https://doi.org/10.1093/jicru/os13.1.Report24|doi = 10.1093/jicru/os13.1.Report24|title = Report 24|journal = Journal of the International Commission on Radiation Units and Measurements|year = 1976|pages = NP|url-access = subscription}}</ref> the delivered dose should not deviate by more than ± 5% of the prescribed dose. More recently, the new ICRU recommendations in Publication 62<ref>"[https://www.icru.org/report/prescribing-recording-and-reporting-photon-beam-therapy-report-62]"  Prescribing, Recording and Reporting Photon Beam Therapy, accessed July 29, 2021</ref>

Commercially available computerized treatment planning systems are often used in radiotherapy services to perform monitoring unit (MU) calculations to deliver the prescribed dose to the patient. As only a part of the total dose uncertainty originates from the calculation process in treatment planning, the tolerance for accuracy of planning systems has to be smaller.<ref>{{Cite journal|last1=Gibbons|first1=John P.|last2=Antolak|first2=John A.|last3=Followill|first3=David S.|last4=Huq|first4=M. Saiful|last5=Klein|first5=Eric E.|last6=Lam|first6=Kwok L.|last7=Palta|first7=Jatinder R.|last8=Roback|first8=Donald M.|last9=Reid|first9=Mark|last10=Khan|first10=Faiz M.|date=March 2014|title=Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71|journal=Medical Physics|volume=41|issue=3|pages=031501|doi=10.1118/1.4864244|issn=2473-4209|pmc=5148083|pmid=24593704|bibcode=2014MedPh..41c1501G }}</ref><ref name=":0">{{Cite journal|last1=Zhu|first1=Timothy C.|last2=Stathakis|first2=Sotiris|last3=Clark|first3=Jennifer R.|last4=Feng|first4=Wenzheng|last5=Georg|first5=Dietmar|last6=Holmes|first6=Shannon M.|last7=Kry|first7=Stephen F.|last8=Ma|first8=Chang-Ming Charlie|last9=Miften|first9=Moyed|last10=Mihailidis|first10=Dimitris|last11=Moran|first11=Jean M.|date=2021|title=Report of AAPM Task Group 219 on independent calculation-based dose/MU verification for IMRT|journal=Medical Physics|language=en|volume=48|issue=10|pages=e808–e829|doi=10.1002/mp.15069|pmid=34213772|s2cid=235710976|issn=2473-4209|doi-access=free}}</ref>

Publications on quality assurance in radiotherapy have recommended routine checks of MU calculations through independent manual calculation. This type of verification can also increase confidence in the accuracy of the algorithm and in the [[data integrity]] of the beams used, in addition to providing an indication of the limitations of the application of conventional dose calculation algorithms used by planning systems.<ref>"[https://pubmed.ncbi.nlm.nih.gov/9745794/]"  An independent check method of radiotherapy computer plan derived monitor units, accessed July 29, 2021</ref> Table 1 lists MU calculation software manufacturers.
{| class="wikitable"
|+TABLE 1. Commercially available 2nd MU verification software<ref name=":0" />
!Manufacturer
!Software
!Algorithm
!Supported
!Website
|-
|LAP Laser
|RadCalc
|Modified Clarkson
|IMRT
VMAT

TomoTherapy

CyberKnife

Halcyon
|https://www.lap-laser.com/
|-
|Varian Medical Systems
|Mobius
|Collapsed Cone Convolution/Superposition
|IMRT
VMAT

TomoTherapy

CyberKnife

Halcyon
|https://www.varian.com/
|-
|Standard Imaging
|IMSure
|Three Source Model
|IMRT
VMAT
|https://www.standardimaging.com/
|-
|PTW Freiburg
|Diamond
|Modified Clarkson
|IMRT
VMAT
|https://www.ptwdosimetry.com/en/
|-
|Sun Nuclear
|DoseCHECK 
|Collapsed Cone Convolution/Superposition
|IMRT
VMAT

TomoTherapy

Halcyon
|https://www.sunnuclear.com/
|-
|RT Medical Systems
|RT Connect
|Modified Clarkson
|3D, 2D
IMRT

VMAT

TomoTherapy

CyberKnife

Halcyon
|http://rtmedical.com.br/
|-
|Math Resolutions LLC 
|DosimetryCheck
|Modified Clarkson
|IMRT
VMAT
|http://www.mathresolutions.com/
|-
|MUCheck
|Oncology Data Systems
|Modified Clarkson
|IMRT
VMAT

TomoTherapy

CyberKnife
|https://mucheck.com/odshome/
|}


== References ==
{{Reflist}}

{{Radiation protection|state=uncollapsed}}

{{DEFAULTSORT:Monitor Unit}}
[[Category:Radiation therapy]]
[[Category:Medical physics]]
[[Category:Oncology]]
[[Category:X-rays]]