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Optimisation of Varian TrueBeam head, thorax and pelvis CBCT based on patient size

Published online by Cambridge University Press:  05 April 2021

Christina E. Agnew Open the ORCID record for Christina E. Agnew [Opens in a new window] ,
Candice McCallum ,
Gail Johnston ,
Adam Workman  and
Denise M. Irvine
Christina E. Agnew*
Affiliation:
Radiotherapy Physics, Belfast Health and Social Care Trust, Northern Ireland Cancer Centre, BelfastBT9 7AB, Northern Ireland
Candice McCallum
Affiliation:
Radiotherapy Physics, Belfast Health and Social Care Trust, Northern Ireland Cancer Centre, BelfastBT9 7AB, Northern Ireland
Gail Johnston
Affiliation:
Radiation Protection and Radiological Sciences and Imaging, Belfast Health and Social Care Trust, Forster Green Hospital, BelfastBT8 6GR, Northern Ireland
Adam Workman
Affiliation:
Radiation Protection and Radiological Sciences and Imaging, Belfast Health and Social Care Trust, Forster Green Hospital, BelfastBT8 6GR, Northern Ireland
Denise M. Irvine
Affiliation:
Radiotherapy Physics, Belfast Health and Social Care Trust, Northern Ireland Cancer Centre, BelfastBT9 7AB, Northern Ireland
*
Author for correspondence: Christina E. Agnew, Radiotherapy Physics, Belfast Health and Social Care Trust, Northern Ireland Cancer Centre, BelfastBT9 7AB, Northern Ireland. Tel: +44 28 95048352. E-mail: Christina.agnew@belfasttrust.hscni.net
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Abstract

Purpose:

The aim of this study was to optimise patient dose and image quality of Varian TrueBeam cone beam computed tomography (CBCT) pelvis, thorax and head and neck (H&N) images based on patient size.

Methods:

An elliptical phantom of small, medium and large size was designed representative of a local population of pelvis, thorax and H&N patients. The phantom was used to establish the relationship between image noise, CT and CBCT exposure settings. Using this insight, clinical images were optimised in phases and the image quality graded qualitatively by radiographers. At each phase, the time required to match the images was recorded from the record and verify system.

Results:

Average patient diameter was a suitable metric to categorise patient size. Phantom measurements showed the power relationship between noise and CBCT exposure settings of value −0·15, −0·35 and −0·43 for thorax, pelvis and H&N, respectively. These quantitative phantom measurements provided confidence that phased variation of ~±20% in mAs should result in clinically usable images. Qualitative assessment of almost 2000 images reduced the exposure settings in H&N images by −50%, thorax images by up to −66% and pelvis images by up to −80%. These optimised CBCT settings did not affect the time required to match images.

Findings:

Varian TrueBeam CBCT mAs settings have been optimised for dose and image quality based on patient size for three treatment sites: pelvis, thorax and H&N. Quantitative phantom measurements provided insight into the magnitude of change to implement clinically. The final optimised exposure settings were determined from radiographer qualitative image assessment.

Keywords

CBCTdose optimisationradiotherapy imaging
Type
Original Article
Information
Journal of Radiotherapy in Practice , Volume 20 , Issue 3 , September 2021 , pp. 248 - 256
Copyright
© The Author(s), 2021. Published by Cambridge University Press

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