title: Rectal complication probability from composite volumes derived from daily cone beam computed tomography in prostate cancer radiotherapy.
abstract: OBJECTIVE
  The aim of this study is to investigate the rectal complication probabilities for various rectum volumes with intensity-modulated radiation therapy (IMRT) and three-dimensional conformal radiotherapy (3D-CRT) in patients undergoing prostate cancer radiotherapy.
  
  
  METHODS
  Thirteen patients undergoing prostate cancer radiotherapy were consecutively selected for this study. All patients were treated with IMRT to a dose of 78 Gy in 39 fractions. Three different rectum volumes: (i) planned rectum (plan-rectum) (ii) Boolean sum of rectum volume based on the cone-beam computed tomography (CBCT) for first five fractions (planning organ at risk volumes [PRV]-CBCT-5), (iii) Boolean sum of rectum volume from all the CBCTs (PRV-CBCT-All) in addition to an average rectal complication (PRV-CBCT-AV) were used for computing the probabilities of rectal complications. To assess the rectal complications with 3D-CRT, a five-field plan was generated for comparison with IMRT. The Lyman-Kutcher-Burman (LKB) normal tissue complication probability (NTCP) model was used to assess the rectal complications for all of the defined rectal volumes.
  
  
  RESULTS
  The NTCPs for rectum as assessed from plan-rectum, PRV-CBCT-5, PRV-CBCT-All, and PRV-CBCT-AV with IMRT were 9.71% ±4.69%, 16.34% ±9.51%, 19.39% ±9.71%, and 12.81% ±7.22%, respectively. Similarly, with 3D-CRT, the NTCPs were 17.41% ±10.44%, 19.61% ±11.08%, 21.03% ±11.06%, and 17.72% ±10.29%, respectively.
  
  
  CONCLUSIONS
  Our results showed that the rectal complications are reduced significantly with IMRT as compared to 3D-CRT. As such, the analyses of NTCP with various defined composite rectum volumes indicate that IMRT requires image-guided adaptive radiotherapy as opposed to 3D-CRT.
authors.affiliation: Department of Physical Sciences, Peter MacCallum Cancer Centre, St. Andrew Place, East Melboure, Vic 3002; Bendigo Radiotherapy Centre, Peter MacCallum Cancer Centre, Stewart Street, Vic 3550; School of Med Sciences, RMIT University, Bundoora Campus, Bundoora, Vic 3083, Australia.
authors.forename: Ramachandran
authors.initials: R
authors.lastname: Prabhakar
authors.forename: Richard
authors.initials: R
authors.lastname: Oates
authors.forename: Jones
authors.initials: J
authors.lastname: Daryl
authors.forename: Joe
authors.initials: J
authors.lastname: Chang
authors.forename: Moshi
authors.initials: M
authors.lastname: Geso
authors.forename: Jim
authors.initials: J
authors.lastname: Cramb
mesh_terms: D054893:Cone-Beam Computed Tomography / Q000009:adverse effects*; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000150:complications / Q000473:pathology / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000473:pathology; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000009:adverse effects*; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects*; D012007:Rectum / Q000473:pathology / Q000528:radiation effects