title: Identifying afterloading PDR and HDR brachytherapy errors using real-time fiber-coupled Al(2)O(3):C dosimetry and a novel statistical error decision criterion.
abstract: OBJECTIVE
  The feasibility of a real-time in vivo dosimeter to detect errors has previously been demonstrated. The purpose of this study was to: (1) quantify the sensitivity of the dosimeter to detect imposed treatment errors under well controlled and clinically relevant experimental conditions, and (2) test a new statistical error decision concept based on full uncertainty analysis.
  
  
  METHODS
  Phantom studies of two gynecological cancer PDR and one prostate cancer HDR patient treatment plans were performed using tandem ring applicators or interstitial needles. Imposed treatment errors, including interchanged pairs of afterloader guide tubes and 2-20mm source displacements, were monitored using a real-time fiber-coupled carbon doped aluminum oxide (Al(2)O(3):C) crystal dosimeter that was positioned in the reconstructed tumor region. The error detection capacity was evaluated at three dose levels: dwell position, source channel, and fraction. The error criterion incorporated the correlated source position uncertainties and other sources of uncertainty, and it was applied both for the specific phantom patient plans and for a general case (source-detector distance 5-90 mm and position uncertainty 1-4mm).
  
  
  RESULTS
  Out of 20 interchanged guide tube errors, time-resolved analysis identified 17 while fraction level analysis identified two. Channel and fraction level comparisons could leave 10mm dosimeter displacement errors unidentified. Dwell position dose rate comparisons correctly identified displacements ≥ 5mm.
  
  
  CONCLUSIONS
  This phantom study demonstrates that Al(2)O(3):C real-time dosimetry can identify applicator displacements ≥ 5mm and interchanged guide tube errors during PDR and HDR brachytherapy. The study demonstrates the shortcoming of a constant error criterion and the advantage of a statistical error criterion.
authors.affiliation: Radiation Research Division, Technical University of Denmark, Roskilde, Denmark. guke@risoe.dtu.dk
authors.forename: Gustavo
authors.initials: G
authors.lastname: Kertzscher
authors.forename: Claus E
authors.initials: CE
authors.lastname: Andersen
authors.forename: Frank-André
authors.initials: FA
authors.lastname: Siebert
authors.forename: Søren Kynde
authors.initials: SK
authors.lastname: Nielsen
authors.forename: Jacob C
authors.initials: JC
authors.lastname: Lindegaard
authors.forename: Kari
authors.initials: K
authors.lastname: Tanderup
mesh_terms: D000537:Aluminum Oxide; D001918:Brachytherapy / Q000295:instrumentation / Q000592:standards*; D019583:Dose Fractionation, Radiation; D004867:Equipment Design; D005240:Feasibility Studies; D005260:Female; D005833:Genital Neoplasms, Female / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D019300:Medical Errors / Q000517:prevention & control*; D009010:Monte Carlo Method; D009339:Needles; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011785:Quality Assurance, Health Care; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D012680:Sensitivity and Specificity; D014025:Titanium
chemical_list: D014025:Titanium; D000537:Aluminum Oxide