title: Technical note: removing the stem effect when performing Ir-192 HDR brachytherapy in vivo dosimetry using plastic scintillation detectors: a relevant and necessary step.
abstract: OBJECTIVE
  The purpose of this study was to investigate whether or not a stem effect removal technique is necessary when performing Ir-192 HDR brachytherapy in vivo dosimetry using a scintillation detector.
  
  
  METHODS
  A red-green-blue photodiode connected to a multichannel electrometer was used to detect the light emitted from a plastic scintillation detector (PSD) during irradiation with an Ir-192 HDR brachytherapy source. Accuracy in dose measurement was compared with and without the use of stem effect removal techniques. Monochromatic and polychromatic filtration techniques were studied. An in-house template was built for accurate positioning of catheters in which the source and the PSD were inserted. Dose distribution was measured up to 5 cm from source to detector in the radial and longitudinal directions.
  
  
  RESULTS
  The authors found the stem effect to be particularly important when the source was close to the optical fiber guide and far from the scintillation component of the detector. It can account for up to (72 +/- 3)% of the signal under clinically relevant conditions. The polychromatic filtration outperformed the monochromatic filtration as well as the absence of filtration in regard to dose measurement accuracy.
  
  
  CONCLUSIONS
  It is necessary to implement a stem effect removal technique when building a PSD for in vivo dosimetry during Ir-192 HDR brachytherapy. The PSD that the authors have developed for this study would be suitable for such an application.
authors.affiliation: Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Boulevard, Unit 94, Houston, Texas 77030, USA.
authors.forename: Francois
authors.initials: F
authors.lastname: Therriault-Proulx
authors.forename: Sam
authors.initials: S
authors.lastname: Beddar
authors.forename: Tina M
authors.initials: TM
authors.lastname: Briere
authors.forename: Louis
authors.initials: L
authors.lastname: Archambault
authors.forename: Luc
authors.initials: L
authors.lastname: Beaulieu
mesh_terms: D016477:Artifacts; D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D003116:Color; D007496:Iridium Radioisotopes / Q000627:therapeutic use*; D010969:Plastics; D011874:Radiometry; D011879:Radiotherapy Dosage; D012588:Scintillation Counting / Q000295:instrumentation / Q000379:methods*
chemical_list: D007496:Iridium Radioisotopes; D010969:Plastics