title: HDR 192Ir source speed measurements using a high speed video camera.
abstract: OBJECTIVE
  The dose delivered with a HDR (192)Ir afterloader can be separated into a dwell component, and a transit component resulting from the source movement. The transit component is directly dependent on the source speed profile and it is the goal of this study to measure accurate source speed profiles.
  
  
  METHODS
  A high speed video camera was used to record the movement of a (192)Ir source (Nucletron, an Elekta company, Stockholm, Sweden) for interdwell distances of 0.25-5 cm with dwell times of 0.1, 1, and 2 s. Transit dose distributions were calculated using a Monte Carlo code simulating the source movement.
  
  
  RESULTS
  The source stops at each dwell position oscillating around the desired position for a duration up to (0.026 ± 0.005) s. The source speed profile shows variations between 0 and 81 cm/s with average speed of ∼ 33 cm/s for most of the interdwell distances. The source stops for up to (0.005 ± 0.001) s at nonprogrammed positions in between two programmed dwell positions. The dwell time correction applied by the manufacturer compensates the transit dose between the dwell positions leading to a maximum overdose of 41 mGy for the considered cases and assuming an air-kerma strength of 48 000 U. The transit dose component is not uniformly distributed leading to over and underdoses, which is within 1.4% for commonly prescribed doses (3-10 Gy).
  
  
  CONCLUSIONS
  The source maintains its speed even for the short interdwell distances. Dose variations due to the transit dose component are much lower than the prescribed treatment doses for brachytherapy, although transit dose component should be evaluated individually for clinical cases.
authors.affiliation: Instituto de Pesquisas Energéticas e Nucleares-IPEN-CNEN/SP, São Paulo 05508-000, Brazil and Department of Radiation Oncology (MAASTRO), GROW School for Oncology and Developmental Biology, Maastricht University Medical Center, Maastricht 6201 BN, The Netherlands.
authors.forename: Gabriel P
authors.initials: GP
authors.lastname: Fonseca
authors.affiliation: Instituto de Pesquisas Energéticas e Nucleares-IPEN-CNEN/SP, São Paulo 05508-000, Brazil.
authors.forename: Rodrigo S S
authors.initials: RS
authors.lastname: Viana
authors.affiliation: Department of Radiation Oncology (MAASTRO), GROW School for Oncology and Developmental Biology, Maastricht University Medical Center, Maastricht 6201 BN, The Netherlands.
authors.forename: Mark
authors.initials: M
authors.lastname: Podesta
authors.affiliation: Hospital das Clínicas da Universidade de São Paulo-HC/FMUSP, São Paulo 05508-000, Brazil.
authors.forename: Rodrigo A
authors.initials: RA
authors.lastname: Rubo
authors.affiliation: Hospital das Clínicas da Universidade de São Paulo-HC/FMUSP, São Paulo 05508-000, Brazil.
authors.forename: Camila P
authors.initials: CP
authors.lastname: de Sales
authors.affiliation: Department of Radiation Oncology (MAASTRO), GROW School for Oncology and Developmental Biology, Maastricht University Medical Center, Maastricht 6201 BN, The Netherlands and Research Group NuTeC, CMK, Hasselt University, Agoralaan Gebouw H, Diepenbeek B-3590, Belgium.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Reniers
authors.affiliation: Instituto de Pesquisas Energéticas e Nucleares-IPEN-CNEN/SP, São Paulo 05508-000, Brazil.
authors.forename: Hélio
authors.initials: H
authors.lastname: Yoriyaz
authors.affiliation: Department of Radiation Oncology (MAASTRO), GROW School for Oncology and Developmental Biology, Maastricht University Medical Center, Maastricht 6201 BN, The Netherlands and Medical Physics Unit, Department of Oncology, McGill University, Montréal, Québec H3G 1A4, Canada.
authors.forename: Frank
authors.initials: F
authors.lastname: Verhaegen
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation*; D003198:Computer Simulation; D007496:Iridium Radioisotopes / Q000627:therapeutic use*; D009010:Monte Carlo Method; D009038:Motion; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods*; D013997:Time Factors; D014741:Video Recording / Q000295:instrumentation* / Q000379:methods*
chemical_list: D007496:Iridium Radioisotopes