title: Feasibility of and rectal dosimetry improvement with the use of SpaceOAR® hydrogel for dose-escalated prostate cancer radiotherapy.
abstract: BACKGROUND
  The aim of this study was to investigate the feasibility of injecting a temporary spacer between the rectum and the prostate and to quantify the degree of rectal dosimetric improvement that might result.
  
  
  METHODS
  Ten patients underwent CT and MRI before and after injection of 10 cc of hydrogel and at completion of radiotherapy. Hydrogel was injected under general anaesthetic using a transperineal approach. The primary endpoints were perioperative toxicity and rectal dosimetry (V80, V75, V70, V65, V40 and V30). Secondary endpoints were acute gastrointestinal toxicity during and 3 months following radiotherapy and the stability of the hydrogel. Treatment for all patients was planned incorporating volumetric modulated arc therapy with a D95 of 80 Gy in 40 fractions to the prostate and proximal seminal vesicles on both the pre- and post-hydrogel scans. Toxicity was scored with the Common Terminology Criteria, v. 3.0.
  
  
  RESULTS
  In the first 24 h, two patients described an increase in bowel movement frequency. The comparison plans had identical prescription doses. Rectal doses were significantly lower for all hydrogel patients for all dose endpoints (V80 = 7% vs. 0.1%, V75 = 10.3% vs. 1.1%, V70 = 13.2% vs. 2.7%, V65 = 15.8% vs. 4.6%, V40 = 35.2% vs. 23.3%, V30 = 52.6% vs. 38.5%; P < 0.001). Post-treatment MRI showed gel stability. Grade 1 bowel toxicity was reported in six patients during radiotherapy and two patients at 3 months' follow-up. No Grade 2 or Grade 3 acute bowel toxicity was reported.
  
  
  CONCLUSIONS
  SpaceOAR hydrogel was successfully injected in 10 patients with minimal side effects. Rectal dosimetry was significantly improved in all patients. This study has been extended to 30 patients with longer follow-up planned.
authors.affiliation: Northern Sydney Cancer Centre, Royal North Shore Hospital, Sydney, New South Wales, Australia.
authors.forename: Kirsten
authors.initials: K
authors.lastname: van Gysen
authors.forename: Andrew
authors.initials: A
authors.lastname: Kneebone
authors.forename: Florencia
authors.initials: F
authors.lastname: Alfieri
authors.forename: Linxin
authors.initials: L
authors.lastname: Guo
authors.forename: Thomas
authors.initials: T
authors.lastname: Eade
mesh_terms: D000368:Aged; D019583:Dose Fractionation, Radiation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D005240:Feasibility Studies; D006801:Humans; D020100:Hydrogels / Q000528:radiation effects; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011832:Radiation Injuries / Q000175:diagnosis / Q000209:etiology* / Q000517:prevention & control*; D011874:Radiometry / Q000295:instrumentation*; D020266:Radiotherapy, Conformal / Q000009:adverse effects*; D012002:Rectal Diseases / Q000175:diagnosis / Q000209:etiology* / Q000517:prevention & control*; D012007:Rectum / Q000528:radiation effects; D016896:Treatment Outcome
chemical_list: D020100:Hydrogels
keywords: prostate cancer; radiation therapy; spacer gel; toxicity; treatment planning