title: Dose-effect relationships for individual pelvic floor muscles and anorectal complaints after prostate radiotherapy.
abstract: OBJECTIVE
  To delineate the individual pelvic floor muscles considered to be involved in anorectal toxicity and to investigate dose-effect relationships for fecal incontinence-related complaints after prostate radiotherapy (RT).
  
  
  METHODS
  In 48 patients treated for localized prostate cancer, the internal anal sphincter (IAS) muscle, the external anal sphincter (EAS) muscle, the puborectalis muscle (PRM), and the levator ani muscles (LAM) in addition to the anal wall (Awall) and rectal wall (Rwall) were retrospectively delineated on planning computed tomography scans. Dose parameters were obtained and compared between patients with and without fecal urgency, incontinence, and frequency. Dose-effect curves were constructed. Finally, the effect of an endorectal balloon, which was applied in 28 patients, was investigated.
  
  
  RESULTS
  The total volume of the pelvic floor muscles together was about three times that of the Awall. The PRM was exposed to the highest RT dose, whereas the EAS received the lowest dose. Several anal and rectal dose parameters, as well as doses to all separate pelvic floor muscles, were associated with urgency, while incontinence was associated mainly with doses to the EAS and PRM. Based on the dose-effect curves, the following constraints regarding mean doses could be deduced to reduce the risk of urgency: ≤ 30 Gy to the IAS; ≤ 10 Gy to the EAS; ≤ 50 Gy to the PRM; and ≤ 40 Gy to the LAM. No dose-effect relationships for frequency were observed. Patients treated with an endorectal balloon reported significantly less urgency and incontinence, while their treatment plans showed significantly lower doses to the Awall, Rwall, and all pelvic floor muscles.
  
  
  CONCLUSIONS
  Incontinence-related complaints show specific dose-effect relationships to individual pelvic floor muscles. Dose constraints for each muscle can be identified for RT planning. When only the Awall is delineated, substantial components of the continence apparatus are excluded.
authors.affiliation: Department of Radiation Oncology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands. r.smeenk@rther.umcn.nl
authors.forename: Robert Jan
authors.initials: RJ
authors.lastname: Smeenk
authors.forename: Aswin L
authors.initials: AL
authors.lastname: Hoffmann
authors.forename: Wim P M
authors.initials: WP
authors.lastname: Hopman
authors.forename: Emile N J Th
authors.initials: EN
authors.lastname: van Lin
authors.forename: Johannes H A M
authors.initials: JH
authors.lastname: Kaanders
mesh_terms: D000368:Aged; D001003:Anal Canal / Q000000981:diagnostic imaging / Q000528:radiation effects*; D002404:Catheterization / Q000295:instrumentation / Q000379:methods; D004307:Dose-Response Relationship, Radiation; D005242:Fecal Incontinence / Q000209:etiology* / Q000517:prevention & control; D006801:Humans; D008297:Male; D009132:Muscles / Q000528:radiation effects*; D017773:Pelvic Floor / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects*