title: Dosimetric impact assessment using a general algorithm in geant4 simulations for a complex-shaped multileaf collimator.
abstract: OBJECTIVE
  We have developed an inhouse algorithm for the multileaf collimator (MLC) geometry model construction with an appropriate accuracy for dosimetric tests. Our purpose is to build a complex type of MLC and analyze the influence of the modeling parameters on the dose calculation.
  
  
  METHODS
  Using radiochromic films as detector the following tests were done: (I) Density test field: to compare measured and calculated dose distributions in order to determine the tungsten alloy physical density value. (II) Leaf ends test field: to verify the penumbra shape sensitivity against the discretization level set to simulate the curved leaf ends. (III) MLC-closed field: to obtain the value of the air gap between opposite leaves for a closed configuration which completes the modeling of the MLC leakage radiation. (IV) Picket-fence field: to fit the leaf tilt angle with respect of the divergent ray emerging from the source.
  
  
  RESULTS
  For a 18.5g/cm3density value we have obtained a maximum, minimum and mean leakage values of 0.43%, 0.36% and 0.38%, similar to the experimental ones. The best discretization level in the leaf ends field shows a 5.51mm FWHM, very close to the measured value (5.49mm). An air gap of 370μm has been used in the simulation for the separation between opposite leaves. Using a 0.44° tilt angle, we found the same pattern as the experimental values.
  
  
  CONCLUSIONS
  Our code can reproduce complex MLC designs with a submilimetric dosimetric accuracy which implies the necessary background for dose calculation of high clinical interest small fields.
authors.affiliation: Dept. Atomic, Molecular and Nuclear Physics, Universidad de Sevilla, Avda. Reina Mercedes s/n, 41012 Seville, Spain. Electronic address: alvpermol@gmail.com.
authors.forename: Á
authors.initials: Á
authors.lastname: Perales
authors.affiliation: Dept. Atomic, Molecular and Nuclear Physics, Universidad de Sevilla, Avda. Reina Mercedes s/n, 41012 Seville, Spain.
authors.forename: M A
authors.initials: MA
authors.lastname: Cortés-Giraldo
authors.affiliation: Dept. Medical Physics, Hospital Universitario Virgen Macarena, Avda. Doctor Fedriani 3, 41009 Seville, Spain.
authors.forename: H
authors.initials: H
authors.lastname: Miras
authors.affiliation: Dept. Medical Physics, Hospital Universitario Virgen Macarena, Avda. Doctor Fedriani 3, 41009 Seville, Spain.
authors.forename: R
authors.initials: R
authors.lastname: Arráns
authors.affiliation: Dept. Atomic, Molecular and Nuclear Physics, Universidad de Sevilla, Avda. Reina Mercedes s/n, 41012 Seville, Spain.
authors.forename: M I
authors.initials: MI
authors.lastname: Gallardo
mesh_terms: D000465:Algorithms; D010315:Particle Accelerators; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted
keywords: Monte Carlo; Multileaf collimator; Tilt angle; geant4