Monitor unit: Difference between revisions
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<ref>"[https://doi.org/10.1093/jicru/os13.1.Report24]" Determination of Absorbed Dose in a Patient Irradiated by Beams of X or Gamma Rays in Radiotheraphy Procedures, accessed July 29, 2021</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> |
<ref>"[https://doi.org/10.1093/jicru/os13.1.Report24]" Determination of Absorbed Dose in a Patient Irradiated by Beams of X or Gamma Rays in Radiotheraphy Procedures, accessed July 29, 2021</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> |
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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. |
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|last=Gibbons|first=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=2014-03|title=Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71|url=https://pubmed.ncbi.nlm.nih.gov/24593704/|journal=Medical Physics|volume=41|issue=3|pages=031501|doi=10.1118/1.4864244|issn=2473-4209|pmc=5148083|pmid=24593704}}</ref><ref name=":0">{{Cite journal|last=Zhu|first=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|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/mp.15069|journal=Medical Physics|language=en|volume=48|issue=10|pages=e808–e829|doi=10.1002/mp.15069|issn=2473-4209}}</ref> |
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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. |
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. |
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[[Category:Radiation therapy]] |
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Revision as of 00:06, 15 February 2022
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 chambers that measure the dose delivered by a beam and are built into the treatment head of radiotherapy linear accelerators.[1]
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.[2][3]
The most common definitions are:[4]
- The monitor chamber reads 100 MU when an absorbed dose of 1 gray (100 rads) is delivered to a point at the depth of maximum dose in a water-equivalent phantom whose surface is at the isocenter of the machine (i.e. usually at 100 cm from the source) with a field size at the surface of 10 cm × 10 cm.
- The monitor chamber reads 100 MU when an absorbed dose of 1 Gy (100 rad) 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 cm × 10 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 treatment 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 [5]
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 [6], the delivered dose should not deviate by more than ± 5% of the prescribed dose. More recently, the new ICRU recommendations in Publication 62[7]
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.[8][9]
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[10]. Table 1 lists MU calculation software manufacturers.
| 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
- ^ Halperin, Edward C.; Perez, Carlos A.; Brady, Luther W. (2008). Perez and Brady's principles and practice of radiation oncology (5th ed.). Philadelphia: Lippincott Williams & Wilkins. p. 152. ISBN 9780781763691.
- ^ Lillicrap, S C; Owen, B; Williams, J R; Williams, P C (1 October 1990). "Code of Practice for high-energy photon therapy dosimetry based on the NPL absorbed dose calibration service". Physics in Medicine and Biology. 35 (10): 1355–1360. doi:10.1088/0031-9155/35/10/301.
- ^ Nath, Ravinder; Biggs, Peter J.; Bova, Frank J.; Ling, C. Clifton; Purdy, James A.; van de Geijn, Jan; Weinhous, Martin S. (July 1994). "AAPM code of practice for radiotherapy accelerators: Report of AAPM Radiation Therapy Task Group No. 45" (PDF). Medical Physics. 21 (7): 1093–1121. doi:10.1118/1.597398. PMID 7968843.
- ^ Mayles, Philip; Nahum, Alan; Rosenwald, Jean-Claude (2007). "Chapter 20: From Measurements to Calculations". Handbook of Radiotherapy Physics - Theory and Practice. ISBN 0-7503-0860-5.
- ^ ed. International Atomic Energy Agency., "Commissioning and Quality Assurance of Computerized Planning Systems for Radiation Treatment of Cancer"
- ^ "[1]" Determination of Absorbed Dose in a Patient Irradiated by Beams of X or Gamma Rays in Radiotheraphy Procedures, accessed July 29, 2021
- ^ "[2]" Prescribing, Recording and Reporting Photon Beam Therapy, accessed July 29, 2021
- ^ Gibbons, John P.; Antolak, John A.; Followill, David S.; Huq, M. Saiful; Klein, Eric E.; Lam, Kwok L.; Palta, Jatinder R.; Roback, Donald M.; Reid, Mark; Khan, Faiz M. (2014-03). "Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71". Medical Physics. 41 (3): 031501. doi:10.1118/1.4864244. ISSN 2473-4209. PMC 5148083. PMID 24593704.
{{cite journal}}: Check date values in:|date=(help) - ^ a b Zhu, Timothy C.; Stathakis, Sotiris; Clark, Jennifer R.; Feng, Wenzheng; Georg, Dietmar; Holmes, Shannon M.; Kry, Stephen F.; Ma, Chang-Ming Charlie; Miften, Moyed; Mihailidis, Dimitris; Moran, Jean M. (2021). "Report of AAPM Task Group 219 on independent calculation-based dose/MU verification for IMRT". Medical Physics. 48 (10): e808–e829. doi:10.1002/mp.15069. ISSN 2473-4209.
- ^ "[3]" An independent check method of radiotherapy computer plan derived monitor units, accessed July 29, 2021
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