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The effect of megavoltage field size on intrafraction cone-beam CT image quality

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Abstract

To investigate the effects of scatter from a megavoltage treatment beam on intrafraction cone beam CT (CBCT) image quality. The effects of treatment beam field size and phantom geometry were investigated as well as the clinical success of IFI. Intrafraction imaging (IFI) was performed on four phantoms with four different MV field sizes using a 6 MV FFF source. The image quality of the intrafraction CBCT images was compared to that of a baseline CBCT (i.e. with no treatment beam on) and quantified using noise and low contrast visibility. Increasing the kV tube current was explored as a possible method to reduce noise induced by the MV photon scatter in the intrafraction-CBCTs. The clinical success of all IFI patients over a 2 month period was reviewed. Intrafraction-CBCT image quality and low-contrast visibility deteriorated as MV field size increased. The extent of image degradation was found to depend on the mass of the phantom resulting in a more pronounced effect for a pelvic phantom than a thoracic phantom. While increasing the tube current could reduce the noise in the intrafraction-CBCT images, increasing the current by a factor of 4 failed to reach baseline image quality. Anatomy was found to be the primary indication of clinical IFI failure with all observed failures occurring during abdominal treatments. Image quality was found to decrease with increasing MV field size and decrease with increasing treatment anatomy mass. When considering intrafraction imaging clinically, the primary indicator of IFI failure is treatment anatomy. IFI can be used during chest treatments with high success rates but care must be taken for abdominal treatments and failures should be expected.

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Data availability

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

The author would like to acknowledge the radiation therapists on PA4 at the Princess Alexandra Hospital who helped immensely with data collection for this project. The author would also like to acknowledge Dr Elizabeth Brown for helping with ethics approval and reviewing the manuscript from a radiation therapist perspective, and Luke K Webb who brainstormed ideas with me, talked through problems and generally provided moral support and guidance throughout this project.

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Authors and Affiliations

  1. Princess Alexandra Hospital, Brisbane, QLD, Australia

    Georgia Friend

  2. Sunshine Coast University Hospital, Birtinya, QLD, Australia

    Patrick O’Connor

  3. Herston Biofabrication Institute, Brisbane, QLD, Australia

    Paul Charles

  4. School of Chemistry and Physics, Queensland University of Technology, Brisbane, QLD, Australia

    Paul Charles

Authors
  1. Georgia Friend
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  2. Patrick O’Connor
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  3. Paul Charles
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Corresponding author

Correspondence to Georgia Friend.

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Granted by Metro South HREC Number LNR/2018/QMS/47578.

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The authors declare that they have no conflict of interest.

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Friend, G., O’Connor, P. & Charles, P. The effect of megavoltage field size on intrafraction cone-beam CT image quality. Phys Eng Sci Med 43, 711–717 (2020). https://doi.org/10.1007/s13246-020-00870-7

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  • DOI: https://doi.org/10.1007/s13246-020-00870-7

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