Comparison of dose decrement from intrafraction motion for prone and supine prostate radiotherapy

Jeffrey R. Olsen, Parag J. Parikh, Michael Watts, Camille E. Noel, Kenneth W. Baker, Lakshmi Santanam, Jeff M. Michalski

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Background and purpose: Dose effects of intrafraction motion during prone prostate radiotherapy are unknown. We compared prone and supine treatment using real-time tracking data to model dose coverage. Material and methods: Electromagnetic tracking data were analyzed for 10 patients treated prone, and 15 treated supine, with IMRT for localized prostate cancer. Plans were generated using 0 mm, 3 mm, and 5 mm PTV expansions. Manual beam-hold interventions were applied to reposition the patient when translations exceeded a predetermined threshold. A custom software application (SWIFTER) used intrafraction tracking data acquired during beam-on model delivered prostate dose, by applying rigid body transformations to the prostate structure contoured at simulation within the planned dose cloud. The delivered minimum prostate dose as a percentage of planned dose (Dmin%), and prostate volume covered by the prescription dose as a percentage of the planned volume (VRx%) were compared for prone and supine treatment. Results: Dmin% was reduced for prone treatment for 0 (p = 0.02) and 3 mm (p = 0.03) PTV margins. VRx% was reduced for prone treatment only for 0 mm margins (p = 0.002). No significant differences were found using 5 mm margins. Conclusions: Intrafraction motion has a greater impact on target coverage for prone compared to supine prostate radiotherapy. PTV margins of 3 mm or less correlate with a significant decrease in delivered dose for prone treatment.

Original languageEnglish
Pages (from-to)199-204
Number of pages6
JournalRadiotherapy and Oncology
Issue number2
StatePublished - Aug 2012


  • Calypso
  • Prone
  • Prostate
  • Radiotherapy
  • Tracking


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