title: Analysis of intrafractional organ motion for patients with prostate cancer using soft tissue matching image-guided intensity-modulated radiation therapy by helical tomotherapy.
abstract: OBJECTIVE
  To analyze an intrafractional organ motion for patients with prostate cancer using soft tissue matching by megavolt computed tomography (MVCT) images during the course of image-guided intensity-modulated radiotherapy (IGRT-IMRT) using helical tomotherapy.
  
  
  METHODS
  Data from a total of 10 patients with prostate cancer who received IGRT-IMRT were analyzed, and MVCT images were acquired before and after radiation therapy. Intra-fractional movement and PTV margins for soft tissue matching were calculated by comparing treatment planning images with 740 MVCT images for right-left (RL), superior-inferior (SI), and anteroposterior (AP) dimensions. A total of 74 Gy/37 fractions were administered. A margin to compensate for these variations was calculated using the van Herk's equation.
  
  
  RESULTS
  The intrafractional motion was 0.03 (-1.3 to 1.4) ±0.39 mm in the RL dimension, 0.08 (-1.8 to 0.28) ±0.73 mm in the SI dimension, and 0.52 (-1.8 to 1.8) ±0.63 mm in the AP dimension. The required PTV margin was 0.60 mm, 1.10 mm, and 0.78 mm in the RL, SI, and AP dimensions, respectively. Only one patient exhibited a deviation greater than 5 mm only once in 37 fractions (1/370=0.2%) caused by anal contraction.
  
  
  CONCLUSIONS
  The PTV margin in soft tissue matching IGRT-IMRT by helical tomotherapy for a patient with prostate cancer was 3 mm or less, and our tentative PTV margin of 3-5 mm is sufficient for most patients, if adequate instruction for avoiding anal contraction is given.
authors: Department of Radiology, Kyoto Prefectural University of Medicine, 465 Kajiicho Kawaramachi Hirokoji, Kamigyo-ku, Kyoto, Kyoto 602-8566 Japan. hideya10@hotmail.com.
authors: Kazuki
authors: K
authors: Iwama
authors: Hideya
authors: H
authors: Yamazaki
authors: Takuya
authors: T
authors: Nishimura
authors: Yoshitaka
authors: Y
authors: Oota
authors: Hironori
authors: H
authors: Aibe
authors: Satoaki
authors: S
authors: Nakamura
authors: Hiroyasu
authors: H
authors: Ikeno
authors: Ken
authors: K
authors: Yoshida
authors: Haruumi
authors: H
authors: Okabe
mesh_terms: D019583:Dose Fractionation, Radiation; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D061089:Radiotherapy, Image-Guided; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*
keywords: PTV margin; Tomotherapy; image-guided IMRT; megavolt computed tomography; prostate cancer; soft tissue matching