title: Design and characterization of a new high-dose-rate brachytherapy Valencia applicator for larger skin lesions.
abstract: OBJECTIVE
  The aims of this study were (i) to design a new high-dose-rate (HDR) brachytherapy applicator for treating surface lesions with planning target volumes larger than 3 cm in diameter and up to 5 cm in size, using the microSelectron-HDR or Flexitron afterloader (Elekta Brachytherapy) with a (192)Ir source; (ii) to calculate by means of the Monte Carlo (MC) method the dose distribution for the new applicator when it is placed against a water phantom; and (iii) to validate experimentally the dose distributions in water.
  
  
  METHODS
  The penelope2008 MC code was used to optimize dwell positions and dwell times. Next, the dose distribution in a water phantom and the leakage dose distribution around the applicator were calculated. Finally, MC data were validated experimentally for a (192)Ir mHDR-v2 source by measuring (i) dose distributions with radiochromic EBT3 films (ISP); (ii) percentage depth-dose (PDD) curve with the parallel-plate ionization chamber Advanced Markus (PTW); and (iii) absolute dose rate with EBT3 films and the PinPoint T31016 (PTW) ionization chamber.
  
  
  RESULTS
  The new applicator is made of tungsten alloy (Densimet) and consists of a set of interchangeable collimators. Three catheters are used to allocate the source at prefixed dwell positions with preset weights to produce a homogenous dose distribution at the typical prescription depth of 3 mm in water. The same plan is used for all available collimators. PDD, absolute dose rate per unit of air kerma strength, and off-axis profiles in a cylindrical water phantom are reported. These data can be used for treatment planning. Leakage around the applicator was also scored. The dose distributions, PDD, and absolute dose rate calculated agree within experimental uncertainties with the doses measured: differences of MC data with chamber measurements are up to 0.8% and with radiochromic films are up to 3.5%.
  
  
  CONCLUSIONS
  The new applicator and the dosimetric data provided here will be a valuable tool in clinical practice, making treatment of large skin lesions simpler, faster, and safer. Also the dose to surrounding healthy tissues is minimal.
authors.affiliation: Radiation Oncology Department, La Fe University and Polytechnic Hospital, Valencia 46026, Spain and National Dosimetry Centre (CND), Valencia 46009, Spain.
authors.forename: C
authors.initials: C
authors.lastname: Candela-Juan
authors.affiliation: Elekta Brachytherapy, Veenendaal 3905 TH, The Netherlands.
authors.forename: Y
authors.initials: Y
authors.lastname: Niatsetski
authors.affiliation: Quality Radiation Therapy BV, Zeist 3707 HB, The Netherlands.
authors.forename: R
authors.initials: R
authors.lastname: van der Laarse
authors.affiliation: Department of Radiation Physics, ERESA, Hospital General Universitario, Valencia 46014, Spain.
authors.forename: D
authors.initials: D
authors.lastname: Granero
authors.affiliation: Department of Atomic, Molecular and Nuclear Physics, University of Valencia, Burjassot 46100, Spain.
authors.forename: F
authors.initials: F
authors.lastname: Ballester
authors.affiliation: Radiation Oncology Department, La Fe University and Polytechnic Hospital, Valencia 46026, Spain and Department of Radiotherapy, Clínica Benidorm, Benidorm 03501, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Perez-Calatayud
authors.affiliation: Department of Atomic, Molecular and Nuclear Physics, University of Valencia, Burjassot 46100, Spain and Instituto de Física Corpuscular (UV-CSIC), Burjassot 46100, Spain.
authors.forename: J
authors.initials: J
authors.lastname: Vijande
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation*; D004867:Equipment Design; D006801:Humans; D007496:Iridium Radioisotopes / Q000627:therapeutic use; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012871:Skin Diseases / Q000532:radiotherapy*; D014867:Water
chemical_list: D007496:Iridium Radioisotopes; D014867:Water