title: Comparison of prostate proton treatment planning technique, interfraction robustness, and analysis of single-field treatment feasibility.
abstract: BACKGROUND
  This study compares target coverage robustness among proton therapy plans for prostate cancer patients treated with 2 laterally opposed fields delivered daily or, alternatively, every other day as single lateral fields, using uniform scanning (US), single-field uniform dose (SFUD), pencil beam scanning (PBS) optimized for uniform target coverage only, SFUD PBS optimized for target coverage and organs at risk (OAR) sparing (SFUD-opt), and intensity modulated proton therapy (IMPT).
  
  
  METHODS
  Ten prostate cancer patients treated with proton therapy underwent weekly verification computed tomographic (CT) scans. US, SFUD, SFUD-opt, and IMPT treatment plans were created and recalculated on weekly verification scans evaluating 2-field daily and single-field target coverage and OAR constraints.
  
  
  RESULTS
  The average (±standard deviation) planning target volume conformity index for US, SFUD, SFUD-opt, and IMPT clinical plans was 0.53 ± 0.06, 0.78 ± 0.05, 0.78 ± 0.04, and 0.78 ± 0.03, respectively. The average 2-field internal target volume (ITV) coverage was significantly higher for both US and SFUD when individually compared with SFUD-opt and IMPT. There was no significant difference between US and SFUD ITV coverage when comparing 2-field daily versus single-field daily delivery. The average single-field coverage was greatest using US and SFUD with 99% of the ITV being covered by 96.8% ± 0.9% and 96.7% ± 1.3%, respectively, compared with 95.5% ± 0.7% for SFUD-opt. There were no significant differences among the 4 plans regarding OAR dose constraints assessed.
  
  
  CONCLUSIONS
  Pencil beam scanning techniques are more conformal than US and, when optimized only for uniform target coverage from each field, can be equally as robust relative to anatomic interfraction variations for prostate cancer patients treated with a single field per day technique. The SFUD-opt and IMPT involve highly modulated pencil beam spots and may be less robust to daily interfraction anatomic variations.
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania. Electronic address: Maura.kirk@uphs.upenn.edu.
authors.forename: Maura L
authors.initials: ML
authors.lastname: Kirk
authors.affiliation: Department of Radiation Oncology, ProCure Proton Therapy Center, Somerset, New Jersey.
authors.forename: Shikui
authors.initials: S
authors.lastname: Tang
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Huifang
authors.initials: H
authors.lastname: Zhai
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Neha
authors.initials: N
authors.lastname: Vapiwala
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Curtiland
authors.initials: C
authors.lastname: Deville
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Paul
authors.initials: P
authors.lastname: James
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Justin E
authors.initials: JE
authors.lastname: Bekelman
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: John P
authors.initials: JP
authors.lastname: Christodouleas
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Zelig
authors.initials: Z
authors.lastname: Tochner
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania.
authors.forename: Stefan
authors.initials: S
authors.lastname: Both
mesh_terms: D006801:Humans; D008297:Male; D010934:Planning Techniques; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D061766:Proton Therapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*