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The dosimetric error due to uncorrected tumor rotation during real-time adaptive prostate stereotactic body radiation therapy

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  • Chandrima Sengupta, University of Sydney
  • ,
  • Simon Skouboe
  • Thomas Ravkilde
  • Per Rugaard Poulsen
  • Doan Trang Nguyen, University of Sydney
  • ,
  • Peter B. Greer, Calvary Mater Newcastle
  • ,
  • Trevor Moodie, Crown Princess Mary Cancer Centre
  • ,
  • Nicholas Hardcastle, Peter Maccallum Cancer Centre
  • ,
  • Amy J. Hayden, Crown Princess Mary Cancer Centre
  • ,
  • Sandra Turner, Crown Princess Mary Cancer Centre
  • ,
  • Shankar Siva, Peter Maccallum Cancer Centre
  • ,
  • Keen Hun Tai, University of Melbourne
  • ,
  • Jarad Martin, Calvary Mater Newcastle
  • ,
  • Jeremy T. Booth, Royal North Shore Hospital
  • ,
  • Ricky O'Brien, University of Sydney
  • ,
  • Paul J. Keall, University of Sydney

Background: During prostate stereotactic body radiation therapy (SBRT), prostate tumor translational motion may deteriorate the planned dose distribution. Most of the major advances in motion management to date have focused on correcting this one aspect of the tumor motion, translation. However, large prostate rotation up to 30° has been measured. As the technological innovation evolves toward delivering increasingly precise radiotherapy, it is important to quantify the clinical benefit of translational and rotational motion correction over translational motion correction alone. Purpose: The purpose of this work was to quantify the dosimetric impact of intrafractional dynamic rotation of the prostate measured with a six degrees-of-freedom tumor motion monitoring technology. Methods: The delivered dose was reconstructed including (a) translational and rotational motion and (b) only translational motion of the tumor for 32 prostate cancer patients recruited on a 5-fraction prostate SBRT clinical trial. Patients on the trial received 7.25 Gy in a treatment fraction. A 5 mm clinical target volume (CTV) to planning target volume (PTV) margin was applied in all directions except the posterior direction where a 3 mm expansion was used. Prostate intrafractional translational motion was managed using a gating strategy, and any translation above the gating threshold was corrected by applying an equivalent couch shift. The residual translational motion is denoted as (Formula presented.). Prostate intrafractional rotational motion (Formula presented.) was recorded but not corrected. The dose differences from the planned dose due to (Formula presented.) + (Formula presented.), ΔD((Formula presented.) + (Formula presented.)) and due to (Formula presented.) alone, ΔD((Formula presented.)), were then determined for CTV D98, PTV D95, bladder V6Gy, and rectum V6Gy. The residual dose error due to uncorrected rotation, (Formula presented.) was then quantified: (Formula presented.) = ΔD((Formula presented.) + (Formula presented.)) - ΔD((Formula presented.)). Results: Fractional data analysis shows that the dose differences from the plan (both ΔD((Formula presented.) + (Formula presented.)) and ΔD((Formula presented.))) for CTV D98 was less than 5% in all treatment fractions. ΔD((Formula presented.) + (Formula presented.)) was larger than 5% in one fraction for PTV D95, in one fraction for bladder V6Gy, and in five fractions for rectum V6Gy. Uncorrected rotation, (Formula presented.) induced residual dose error, (Formula presented.), resulted in less dose to CTV and PTV in 43% and 59% treatment fractions, respectively, and more dose to bladder and rectum in 51% and 53% treatment fractions, respectively. The cumulative dose over five fractions, ∑D((Formula presented.) + (Formula presented.)) and ∑D((Formula presented.)), was always within 5% of the planned dose for all four structures for every patient. Conclusions: The dosimetric impact of tumor rotation on a large prostate cancer patient cohort was quantified in this study. These results suggest that the standard 3–5 mm CTV-PTV margin was sufficient to account for the intrafraction prostate rotation observed for this cohort of patients, provided an appropriate gating threshold was applied to correct for translational motion. Residual dose errors due to uncorrected prostate rotation were small in magnitude, which may be corrected using different treatment adaptation strategies to further improve the dosimetric accuracy.

Original languageEnglish
JournalMedical Physics
Pages (from-to)20-29
Number of pages10
Publication statusPublished - Jan 2023

Bibliographical note

Publisher Copyright:
© 2022 University of Sydney. Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.

    Research areas

  • motion management, motion-induced dose error, tumor motion

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