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

15 Scopus citations

Abstract

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
Volume87
Issue number2
DOIs
StatePublished - Oct 1 2013
Externally publishedYes

ASJC Scopus subject areas

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

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