title: Deviations from the planned dose during 48 hours of stepping source prostate brachytherapy caused by anatomical variations.
abstract: OBJECTIVE
  To determine the uncertainties in planned dose associated with catheter and organ movement during 48 hours of stepping source prostate brachytherapy.
  
  
  METHODS
  Pulsed-dose rate (PDR) prostate brachytherapy as a boost is given in 24 pulses every 2 hours, making the total treatment last 48 hours. The entire treatment is based on one plan, created on the planning CT (CT1). Two follow-up CTs (CT2 and CT3) were acquired; halfway through the treatment and at the end of treatment. On these repeat scans the catheters were reconstructed and PTV and OARs were delineated. The original treatment plan was calculated on the repeat CTs. Target coverage V(100%), D(90), dose to 2cm(3) (D2cm(3)) of the rectum and bladder and dose to 0.1cm(3) of the urethra were recorded from the recalculated DVHs.
  
  
  RESULTS
  On the two repeat CTs the V100% decreased -1.5% and -2.3% as compared to the planning CT. For the rectum D2cm(3), the average increase was 14.8% (CT1-CT2) and 17.3% (CT1-CT3). Increase in bladder D2cm(3) was on average 23.1% (CT1-CT2) and 24.8% (CT1-CT3). For the urethra D0.1cm(3) an average decrease of -2% (CT1-CT2) and -3.2% (CT2-CT3) was observed.
  
  
  CONCLUSIONS
  Changes in target coverage during treatment were small and considered clinically irrelevant. However, an overall increase in dose to the OARs was found as compared to the planned dose, which should be taken into account during treatment planning.
authors: Department of Radiation Oncology, Academic Medical Center, Amsterdam, The Netherlands. a.m.dinkla@amc.uva.nl
authors: Anna M
authors: AM
authors: Dinkla
authors: Bradley R
authors: BR
authors: Pieters
authors: Kees
authors: K
authors: Koedooder
authors: Philip
authors: P
authors: Meijnen
authors: Niek
authors: N
authors: van Wieringen
authors: Rob
authors: R
authors: van der Laarse
authors: Johan N
authors: JN
authors: van der Grient
authors: Coen R N
authors: CR
authors: Rasch
authors: Arjan
authors: A
authors: Bel
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D008297:Male; D058958:Organs at Risk; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012007:Rectum / Q000528:radiation effects; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden