Single-fraction prostate stereotactic body radiotherapy: Dose reconstruction with electromagnetic intrafraction motion tracking

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  • Maud Jaccard, University Hospital of Geneva
  • ,
  • Stefanie Ehrbar, University of Zurich, University Hospital Zurich
  • ,
  • Raymond Miralbell, University of Geneva, Teknon Oncologic Institute, University Hospital of Geneva
  • ,
  • Tobias Hagen, University of Zurich, University Hospital Zurich
  • ,
  • Nikolaos Koutsouvelis, University Hospital of Geneva
  • ,
  • Per Poulsen
  • Michel Rouzaud, University of Geneva, University Hospital of Geneva
  • ,
  • Stephanie Tanadini-Lang, University of Zurich, University Hospital Zurich
  • ,
  • Pelagia Tsoutsou, University of Geneva, University Hospital of Geneva
  • ,
  • Matthias Guckenberger, University of Zurich, University Hospital Zurich
  • ,
  • Thomas Zilli, University of Geneva, University Hospital of Geneva

Purpose: To reconstruct the dose delivered during single-fraction urethra-sparing prostate stereotactic body radiotherapy (SBRT) accounting for intrafraction motion monitored by intraprostatic electromagnetic transponders (EMT). Methods: We analyzed data of 15 patients included in the phase I/II “ONE SHOT” trial and treated with a single fraction of 19 Gy to the planning target volume (PTV) and 17 Gy to the urethra planning risk volume. During delivery, prostate motion was tracked with implanted EMT. SBRT was interrupted when a 3-mm threshold was trespassed and corrected unless the offset was transient. Motion-encoded reconstructed (MER) plans were obtained by splitting the original plans into multiple sub-beams with isocenter shifts based on recorded EMT positions, mimicking prostate motion during treatment. We analyzed intrafraction motion and compared MER to planned doses. Results: The median EMT motion range (±SD) during delivery was 0.26 ± 0.09, 0.22 ± 0.14 and 0.18 ± 0.10 cm in the antero-posterior, supero-inferior, and left–right axes, respectively. Treatment interruptions were needed for 8 patients because of target motion beyond limits in the antero-posterior (n = 6) and/or supero-inferior directions (n = 4). Comparing MER vs. original plan there was a median relative dose difference of −1.9% (range, −7.9 to −1.0%) and of +0.5% (−0.3–1.7%) for PTV D98% and D2%, respectively. The clinical target volume remained sufficiently covered with a median D98% difference of −0.3% (−1.6–0.5%). Bladder and rectum dosimetric parameters showed significant differences between original and MER plans, but mostly remained within acceptable limits. Conclusions: The dosimetric impact of intrafraction prostate motion was minimal for target coverage for single-fraction prostate SBRT with real-time electromagnetic tracking combined with beam gating.

OriginalsprogEngelsk
TidsskriftRadiotherapy and Oncology
Vol/bind156
Sider (fra-til)145-152
Antal sider8
ISSN0167-8140
DOI
StatusUdgivet - mar. 2021

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