title: Dosimetric impact of different bladder and rectum filling during prostate cancer radiotherapy.
abstract: BACKGROUND
  The aim of this study was to analyze the influence of volumetric changes of bladder and rectum filling on the 3D dose distribution in prostate cancer radiotherapy.
  
  
  METHODS
  A total of 314 cone-beam CT (CBCT) image data sets from 19 patients were enrolled in this study. For each CBCT, the bladder and rectum were contoured and volume sizes were normalized to those on their original CT. The daily delivered dose was recalculated on the CBCT images and the doses to bladder and rectum were investigated. Linear regression analysis was performed to identify the mean dose change of the volume change using SPSS 19.
  
  
  RESULTS
  The data show that the variances of the normalized volume of the bladder and the rectum are 0.13-0.58 and 0.12-0.50 respectively. The variances of V70Gy, V60Gy, V50Gy, V40Gy and V30Gy of bladder are bigger than those of rectum for 17 patients. The linear regression analysis indicates a 10 % increase in bladder volume will cause a 5.6 % (±4.9 %) reduction in mean dose (p <0.05).
  
  
  CONCLUSIONS
  The bladder's volume change is more significant than that of the rectum for the prostate cancer patient. The rectum volume variations are not significant except for air bubbles, which change the shape and the position of the rectum. The bladder volume variations may cause dose changes proportionately. Monitoring the bladder's volume before fractional treatment delivery will be crucial for accurate dose delivery.
authors.affiliation: Department of Radiation Oncology, Fudan University Shanghai Cancer Center, 270 DongAn Road, Shanghai, 200032, China.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Radiation Oncology, Fudan University Shanghai Cancer Center, 270 DongAn Road, Shanghai, 200032, China.
authors.forename: Zhaozhi
authors.initials: Z
authors.lastname: Yang
authors.affiliation: Department of Radiation Oncology, Fudan University Shanghai Cancer Center, 270 DongAn Road, Shanghai, 200032, China.
authors.forename: Jiazhou
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, Fudan University Shanghai Cancer Center, 270 DongAn Road, Shanghai, 200032, China. jackhuwg@gmail.com.
authors.forename: Weigang
authors.initials: W
authors.lastname: Hu
mesh_terms: D001918:Brachytherapy; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D011182:Postoperative Care; D011379:Prognosis; D011468:Prostatectomy; D011471:Prostatic Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012007:Rectum / Q000528:radiation effects*; D001743:Urinary Bladder / Q000528:radiation effects*
keywords: Cone-beam CT; Dose tracking; Prostate cancer