title: Spacer stability and prostate position variability during radiotherapy for prostate cancer applying a hydrogel to protect the rectal wall.
abstract: OBJECTIVE
  The aim was to evaluate the spacer dimensions and prostate position variability during the course of radiotherapy for prostate cancer.
  
  
  METHODS
  CT scans were performed in a group of 15 patients (G1) after the 10 ml injection of a hydrogel spacer (SpaceOAR™) and 30 patients without a spacer (G2) before the beginning of treatment (CT1) and in the last treatment week, 10-12 weeks following spacer implantation (CT2). Spacer dimensions and displacements were determined and prostate displacements compared.
  
  
  RESULTS
  Mean volume of the hydrogel increased slightly (17%; p<0.01), in 4 of 15 patients >2 cm(3). The average displacement of the hydrogel center of mass was 0.6mm (87%≤ 2.2mm), -0.6mm (100% ≤ 2.2mm) and 1.4mm (87% ≤ 4.3mm) in the x-, y- and z-axes (not significant). The average distance between prostate and anterior rectal wall before/at the end of radiotherapy was 1.6 cm/1.5 cm, 1.2 cm/1.3 cm and 1.0 cm/1.1cm at the level of the base, middle and apex (G1). Prostate position variations were similar comparing G1 and G2, but significant systematic posterior displacements were only found in G2.
  
  
  CONCLUSIONS
  A stable distance between the prostate and anterior rectal wall results during the radiotherapy course after injection of the spacer before treatment planning. Larger posterior prostate displacements could be reduced.
authors: Department of Radiation Oncology, RWTH Aachen University, Aachen, Germany. MPinkawa@ukaachen.de
authors: Michael
authors: M
authors: Pinkawa
authors: Marc D
authors: MD
authors: Piroth
authors: Richard
authors: R
authors: Holy
authors: Nuria
authors: N
authors: Escobar-Corral
authors: Mariana
authors: M
authors: Caffaro
authors: Victoria
authors: V
authors: Djukic
authors: Jens
authors: J
authors: Klotz
authors: Michael J
authors: MJ
authors: Eble
mesh_terms: D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000008:administration & dosage*; D008297:Male; D058958:Organs at Risk / Q000528:radiation effects*; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000528:radiation effects*; D014057:Tomography, X-Ray Computed
chemical_list: D020136:Hydrogel, Polyethylene Glycol Dimethacrylate