title: Who will benefit most from hydrogel rectum spacer implantation in prostate cancer radiotherapy? A model-based approach for patient selection.
abstract: Previous studies confirmed that implantable rectum spacers (IRS) decreased acute gastro-intestinal (GI) toxicity in a significant percentage of prostate cancer patients undergoing intensity modulated radiation therapy (IMRT). We developed decision rules based on clinical risk factors (CRFs) to select those patients who are expected to benefit most from IRS implantation.
  
  
  
  For 26 patients dose distributions with (IMRT+IRS) and without (IMRT-IRS) IRS were calculated. Validated nomograms based on CRFs and dosimetric criteria (anorectal V40Gyand V75Gy) were used to predict probabilities for grade 2-3 (G2-3) acute GI toxicity, G2-3 late rectal bleeding (LRB), G3 LRB, and G2-3 faecal incontinence (FI) for IMRT+IRS and IMRT-IRS. All permutations of CRFs were generated to identify most benefit scenarios (MBS) in which a predicted toxicity reduction of ⩾5% points in ⩾25% of the cohort was present due to IRS implantation.
  
  
  
  IMRT+IRS revealed a significant reduction in V40Gy(p=0.0357) and V75Gy(p<0.0001) relative to IMRT-IRS. For G2-3 acute GI toxicity and G2-3 LRB, the predicted toxicity rates decreased in 17/26 (65%) and 20/26 (77%) patients, and decision rules were derived for 22/32 (69%) and 12/64 (19%) MBS, respectively. From the decision rules, it follows that diabetes status has no impact on G2-3 acute toxicity, and in absence of pre-RT abdominal surgery, the implantation of an IRS is predicted to show no clinically relevant benefit for G2-3 LRB.
  
  
  
  Prostate cancer patients who are expected to benefit most from IRS implantation can be identified prior to IMRT based on their CRFs profile.
authors.affiliation: Department of Radiation Oncology (MAASTRO Clinic), Maastricht University Medical Center, The Netherlands. Electronic address: ben.vanneste@maastro.nl.
authors.forename: Ben G L
authors.initials: BG
authors.lastname: Vanneste
authors.affiliation: Department of Radiation Oncology (MAASTRO Clinic), Maastricht University Medical Center, The Netherlands; Institute of Radiooncology, Helmholtz-Zentrum Dresden-Rossendorf, Germany; Department of Radiotherapy and Radiooncology, University Hospital Carl Gustav Carus at the Technische Universität Dresden, Germany.
authors.forename: Aswin L
authors.initials: AL
authors.lastname: Hoffmann
authors.affiliation: Department of Radiation Oncology (MAASTRO Clinic), Maastricht University Medical Center, The Netherlands.
authors.forename: Emile N
authors.initials: EN
authors.lastname: van Lin
authors.affiliation: Department of Radiation Oncology (MAASTRO Clinic), Maastricht University Medical Center, The Netherlands.
authors.forename: Lien
authors.initials: L
authors.lastname: Van De Voorde
authors.affiliation: Department of Radiation Oncology, University Hospital RWTH Aachen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Pinkawa
authors.affiliation: Department of Radiation Oncology (MAASTRO Clinic), Maastricht University Medical Center, The Netherlands.
authors.forename: Philippe
authors.initials: P
authors.lastname: Lambin
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D005242:Fecal Incontinence / Q000209:etiology / Q000517:prevention & control; D006471:Gastrointestinal Hemorrhage / Q000209:etiology / Q000517:prevention & control; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D049451:Nomograms; D018579:Patient Selection; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000209:etiology / Q000517:prevention & control*; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods; D012007:Rectum / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000528:radiation effects*
chemical_list: D020136:Hydrogel, Polyethylene Glycol Dimethacrylate
keywords: Patient selection; Prostate cancer; Radiotherapy; Rectum spacer; Toxicity prediction