title: Comparison study of intensity modulated arc therapy using single or multiple arcs to intensity modulated radiation therapy for high-risk prostate cancer.
abstract: OBJECTIVE
  Intensity modulated arc therapy (IMAT) is a form of intensity modulated radiation therapy (IMRT) that delivers dose in single or multiple arcs. We compared IMRT plans versus single-arc field (1ARC) and multi-arc fields (3ARC) IMAT plans in high-risk prostate cancer.
  
  
  METHODS
  Sixteen patients were studied. Prostate (PTV P ), right pelvic (PTV RtLN ) and left pelvic lymph nodes (PTV LtLN ), and organs at risk were contoured. PTV P , PTV RtLN , and PTV LtLN received 50.40 Gy followed by a boost to PTV B of 28.80 Gy. Three plans were per patient generated: IMRT, 1ARC, and 3ARC. We recorded the dose to the PTV, the mean dose (D MEAN ) to the organs at risk, and volume covered by the 50% isodose. Efficiency was evaluated by monitor units (MU) and beam on time (BOT). Conformity index (CI), Paddick gradient index, and homogeneity index (HI) were also calculated.
  
  
  RESULTS
  Average Radiation Therapy Oncology Group CI was 1.17, 1.20, and 1.15 for IMRT, 1ARC, and 3ARC, respectively. The plans' HI were within 1% of each other. The D MEAN of bladder was within 2% of each other. The rectum D MEAN in IMRT plans was 10% lower dose than the arc plans (p < 0.0001). The GI of the 3ARC was superior to IMRT by 27.4% (p = 0.006). The average MU was highest in the IMRT plans (1686) versus 1ARC (575) versus 3ARC (1079). The average BOT was 6 minutes for IMRT compared to 1.3 and 2.9 for 1ARC and 3ARC IMAT (p < 0.05).
  
  
  CONCLUSIONS
  For high-risk prostate cancer, IMAT may offer a favorable dose gradient profile, conformity, MU and BOT compared to IMRT.
authors.affiliation: New York Methodist Hospital, Brooklyn, NY, USA. ; Leading Edge Radiation Oncology (LEROS), Weill Medical College of Cornell University, Brooklyn, NY, USA.
authors.forename: Hani
authors.initials: H
authors.lastname: Ashamalla
authors.forename: Ajay
authors.initials: A
authors.lastname: Tejwani
authors.forename: Ioannis
authors.initials: I
authors.lastname: Parameritis
authors.forename: Uma
authors.initials: U
authors.lastname: Swamy
authors.forename: Pei Ching
authors.initials: PC
authors.lastname: Luo
authors.forename: Adel
authors.initials: A
authors.lastname: Guirguis
authors.forename: Amir
authors.initials: A
authors.lastname: Lavaf
keywords: High risk prostate cancer; Intensity modulated arc therapy; Intensity modulated radiation therapy; RapidArc