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Improvements in dose calculation accuracy for small off-axis targets in high dose per fraction tomotherapy

Journal Article


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Abstract


  • Purpose: A recent field safety notice from TomoTherapy detailed the underdosing of small, off-axis

    targets when receiving high doses per fraction. This is due to angular undersampling in the dose

    calculation gantry angles. This study evaluates a correction method to reduce the underdosing, to be

    implemented in the current version (v4.1) of the TomoTherapy treatment planning software.

    Methods: The correction method, termed “Super Sampling” involved the tripling of the number

    of gantry angles from which the dose is calculated during optimization and dose calculation. Radiochromic

    film was used to measure the dose to small targets at various off-axis distances receiving

    a minimum of 21 Gy in one fraction. Measurements were also performed for single small targets at

    the center of the Lucy phantom, using radiochromic film and the dose magnifying glass (DMG).

    Results:Without super sampling, the peak dose deficit increased from 0% to 18% for a 10 mm target

    and 0% to 30% for a 5 mm target as off-axis target distances increased from 0 to 16.5 cm. When

    super sampling was turned on, the dose deficit trend was removed and all peak doses were within 5%

    of the planned dose. For measurements in the Lucy phantom at 9.7 cm off-axis, the positional and

    dose magnitude accuracy using super sampling was verified using radiochromic film and the DMG.

    Conclusions: A correction method implemented in the TomoTherapy treatment planning system

    which triples the angular sampling of the gantry angles used during optimization and dose

    calculation removes the underdosing for targets as small as 5 mm diameter, up to 16.5 cm

    off-axis receiving up to 21 Gy.

Publication Date


  • 2012

Citation


  • Hardcastle, N., Bayliss, A., Wong, J. Hsiu Ding., Rozenfeld, A. & Tome, W. (2012). Improvements in dose calculation accuracy for small off-axis targets in high dose per fraction tomotherapy. Medical Physics, 39 (8), 4788-4794.

Scopus Eid


  • 2-s2.0-84864718772

Ro Full-text Url


  • http://ro.uow.edu.au/cgi/viewcontent.cgi?article=1249&context=eispapers

Ro Metadata Url


  • http://ro.uow.edu.au/eispapers/244

Number Of Pages


  • 6

Start Page


  • 4788

End Page


  • 4794

Volume


  • 39

Issue


  • 8

Abstract


  • Purpose: A recent field safety notice from TomoTherapy detailed the underdosing of small, off-axis

    targets when receiving high doses per fraction. This is due to angular undersampling in the dose

    calculation gantry angles. This study evaluates a correction method to reduce the underdosing, to be

    implemented in the current version (v4.1) of the TomoTherapy treatment planning software.

    Methods: The correction method, termed “Super Sampling” involved the tripling of the number

    of gantry angles from which the dose is calculated during optimization and dose calculation. Radiochromic

    film was used to measure the dose to small targets at various off-axis distances receiving

    a minimum of 21 Gy in one fraction. Measurements were also performed for single small targets at

    the center of the Lucy phantom, using radiochromic film and the dose magnifying glass (DMG).

    Results:Without super sampling, the peak dose deficit increased from 0% to 18% for a 10 mm target

    and 0% to 30% for a 5 mm target as off-axis target distances increased from 0 to 16.5 cm. When

    super sampling was turned on, the dose deficit trend was removed and all peak doses were within 5%

    of the planned dose. For measurements in the Lucy phantom at 9.7 cm off-axis, the positional and

    dose magnitude accuracy using super sampling was verified using radiochromic film and the DMG.

    Conclusions: A correction method implemented in the TomoTherapy treatment planning system

    which triples the angular sampling of the gantry angles used during optimization and dose

    calculation removes the underdosing for targets as small as 5 mm diameter, up to 16.5 cm

    off-axis receiving up to 21 Gy.

Publication Date


  • 2012

Citation


  • Hardcastle, N., Bayliss, A., Wong, J. Hsiu Ding., Rozenfeld, A. & Tome, W. (2012). Improvements in dose calculation accuracy for small off-axis targets in high dose per fraction tomotherapy. Medical Physics, 39 (8), 4788-4794.

Scopus Eid


  • 2-s2.0-84864718772

Ro Full-text Url


  • http://ro.uow.edu.au/cgi/viewcontent.cgi?article=1249&context=eispapers

Ro Metadata Url


  • http://ro.uow.edu.au/eispapers/244

Number Of Pages


  • 6

Start Page


  • 4788

End Page


  • 4794

Volume


  • 39

Issue


  • 8