Effect of intrafraction prostate motion on proton pencil beam scanning delivery: A quantitative assessment

Shikui Tang, Curtiland Deville, James McDonough, Zelig Tochner, Ken Kang Hsin Wang, Neha Vapiwala, Stefan Both

Research output: Contribution to journalArticlepeer-review


Purpose To assess the dosimetric impact caused by the interplay between intrafraction prostate motion and the intermittent delivery of proton pencil beam scanning (PBS). Methods and Materials A cohort of 10 prostate patients was treated with PBS using a bilateral single-field uniform dose (SFUD) modality. Bilateral intensity-modulated proton therapy (IMPT) plans were generated for comparison. Because beam-on time in PBS was intermittent, the actual beam-on time was determined from treatment logs. Prostate motion was generalized according to real-time Calypso tracking data from our previously reported prospective photon trial. We investigated potential dose deviations by considering the interplay effect resulting from the worst-case scenario motion and the PBS delivery sequence. Results For both bilateral-field SFUD and IMPT plans, clinical target volume (CTV) D99% coverage was degraded <2% owing to prostate intrafraction motion when averaged over the course of treatment, but was >10% for the worst fraction. The standard deviation of CTV D99% distribution was approximately 1.2%. The CTV coverage of individual fields in SFUD plans degraded as time elapsed after the initial alignment, owing to prostate drift. Intensity-modulated proton therapy and SFUD demonstrated comparable results when bilateral opposed fields were used. Single-field SFUD plans that were repainted twice, which could reduce half of the treatment time, resulted in similar CTV coverage as bilateral-field plans. Conclusions Intrafraction prostate motion affects the actual delivered dose to CTV; however, when averaged over the course of treatment, CTV D99% coverage degraded only approximately 2% even for the worst-case scenario. The IMPT plan results are comparable to those of the SFUD plan, and similar coverage can be achieved if treated by SFUD 1 lateral field per day when rescanning the field twice to shorten the treatment time and mitigate intrafraction motion.

Original languageEnglish (US)
Pages (from-to)375-382
Number of pages8
JournalInternational Journal of Radiation Oncology Biology Physics
Issue number2
StatePublished - Oct 1 2013

ASJC Scopus subject areas

  • Radiation
  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Cancer Research


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