title: Frequency and predisposing factors for interfractional rectal displacement requiring repeated precaution in prostate cancer patients treated with image-guided intensity-modulated radiation therapy.
abstract: OBJECTIVE
  To investigate the frequency and characteristics of interfractional rectal displacement in patients with prostate cancer treated with image-guided intensity-modulated radiation therapy (IG-IMRT) using helical tomotherapy.
  
  
  METHODS
  Data for a total of 256 patients were analyzed. Megavoltage computed tomography (MVCT) images were acquired before radiation therapy and interfractional rectal displacement was assessed with soft-tissue matching by comparing treatment planning images within 9,445 fractions. Anterior rectal region displacement larger than 5 mm, requiring repeated precaution, was defined as the action level of rectal displacement (ARD).
  
  
  RESULTS
  ARD was identified in 676 (7.2%) out of 9,445 fractions and at least once in 75% (190/256) of patients. Univariate analysis identified three predisposing factors for ARD: body mass index (BMI), rectal volume and prostate volume. Multivariate logistic regression analysis revealed that lower BMI and large rectal volume were statistically significant predictors of ARD. The highest incidence of ARD (13.6% and 9.1%) was found during the initial two weeks of treatment (first five and next five fractions), after which the incidence decreased to 5.96% (p<0.0001).
  
  
  CONCLUSIONS
  ARD was identified in 7.9% of fractions and in 74.8% of patients and was most likely to occur in patients with a low BMI and/or large rectal volume. ARD occurred predominantly during the initial two weeks of treatment and became less likely over time.
authors.affiliation: Department of Radiology, Ujitakeda Hospital, Uji-city, Kyoto, Japan.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Iwama
authors.affiliation: Department of Radiology, Ujitakeda Hospital, Uji-city, Kyoto, Japan Department of Radiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan hideya10@hotmail.com.
authors.forename: Hideya
authors.initials: H
authors.lastname: Yamazaki
authors.affiliation: Department of Radiology, Ujitakeda Hospital, Uji-city, Kyoto, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Nishimura
authors.affiliation: Department of Radiology, Ujitakeda Hospital, Uji-city, Kyoto, Japan.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Oota
authors.affiliation: Department of Radiology, Ujitakeda Hospital, Uji-city, Kyoto, Japan Department of Radiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
authors.forename: Norihiro
authors.initials: N
authors.lastname: Aibe
authors.affiliation: Department of Radiology, Ujitakeda Hospital, Uji-city, Kyoto, Japan Department of Radiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
authors.forename: Satoaki
authors.initials: S
authors.lastname: Nakamura
authors.affiliation: Department of Radiology, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, Japan.
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Ikeno
authors.affiliation: Department of Radiology, Osaka Medical College, Takatsuki City, Osaka, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Yoshida
authors.affiliation: Department of Radiology, Ujitakeda Hospital, Uji-city, Kyoto, Japan.
authors.forename: Haruumi
authors.initials: H
authors.lastname: Okabe
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D061089:Radiotherapy, Image-Guided / Q000009:adverse effects*; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*; D012005:Rectal Prolapse / Q000473:pathology*; D012007:Rectum / Q000473:pathology
keywords: MVCT; Tomotherapy; image-guided IMRT; organ dislocation; prostate cancer