The impact of linac output variations on dose distributions in helical tomotherapy

R T Flynn; M W Kissick; M P Mehta; G H Olivera; R Jeraj; T R Mackie

doi:10.1088/0031-9155/53/2/009

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The impact of linac output variations on dose distributions in helical tomotherapy

Journal article

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Peer reviewed

The impact of linac output variations on dose distributions in helical tomotherapy

R T Flynn, M W Kissick, M P Mehta, G H Olivera, R Jeraj and T R Mackie

Physics in medicine & biology, Vol.53(2), pp.417-430

01/21/2008

DOI: 10.1088/0031-9155/53/2/009

PMCID: PMC2713685

PMID: 18184996

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http://doi.org/10.1088/0031-9155/53/2/009View

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Abstract

It has been suggested for quality assurance purposes that linac output variations for helical tomotherapy (HT) be within ±2% of the long-term average. Due to cancellation of systematic uncertainty and averaging of random uncertainty over multiple beam directions, relative uncertainties in the dose distribution can be significantly lower than those in linac output. The sensitivity of four HT cases with respect to linac output uncertainties was assessed by scaling both modelled and measured systematic and random linac output uncertainties until a dose uncertainty acceptance criterion failed. The dose uncertainty acceptance criterion required the delivered dose to have at least a 95% chance of being within 2% of the planned dose in all of the voxels in the treatment volume. For a random linac output uncertainty of 5% of the long-term mean, the maximum acceptable amplitude of the modelled, sinusoidal, systematic component of the linac output uncertainty for the four cases was 1.8%. Although the measured linac output variations represented values that were outside of the ±2% tolerance, the acceptance criterion did not fail for any of the four cases until the measured linac output variations were scaled by a factor of almost three. Thus the ±2% tolerance in linac output variations for HT is a more conservative tolerance than necessary.

intensity modulation

dose uncertainty

Helical tomotherapy

output variations

dose uniformity

Details

Title: Subtitle: The impact of linac output variations on dose distributions in helical tomotherapy
Creators: R T Flynn - University of Wisconsin Department of Medical Physics, 1530 MSC, 1300 University Ave, Madison, WI 53703, USA
M W Kissick - University of Wisconsin Department of Medical Physics, 1530 MSC, 1300 University Ave, Madison, WI 53703, USA
M P Mehta - University of Wisconsin Department of Human Oncology, 600 Highland Ave, Madison, WI 53792, USA
G H Olivera - TomoTherapy Inc., 1240 Deming Way, Madison, WI 53717, USA
R Jeraj - University of Wisconsin Department of Medical Physics, 1530 MSC, 1300 University Ave, Madison, WI 53703, USA
T R Mackie - University of Wisconsin Department of Medical Physics, 1530 MSC, 1300 University Ave, Madison, WI 53703, USA
Resource Type: Journal article
Publication Details: Physics in medicine & biology, Vol.53(2), pp.417-430
DOI: 10.1088/0031-9155/53/2/009
PMID: 18184996
PMCID: PMC2713685
NLM abbreviation: Phys Med Biol
ISSN: 0031-9155
eISSN: 1361-6560
Language: English
Date published: 01/21/2008
Academic Unit: Radiation Oncology
Record Identifier: 9984047767402771

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