title: Conformal radiotherapy optimization with micromultileaf collimators: comparison with radiosurgery techniques.
abstract: OBJECTIVE
  Conformal radiotherapy (CRT) consists of irradiating the target volume while avoiding the healthy peripheral tissues and organs at risk as far as possible. One technique used to treat intracranial tumors consists of using micromultileaf collimators (MMLCs). Given the dose constraints involved, it is of interest to optimize MMLC irradiation parameters and compare the results of this technique with those of conventional radiosurgery (RT) techniques (Gamma Knife and linear accelerator stereotactic RT).
  
  
  METHODS
  MMLC protocols are optimized in two stages. The orientation of the fields, delimited by a beam's eye view technique, is determined using a genetic algorithm method. The weighting of the fields and subfields when using intensity modulation and the position of the leaves are optimized using a simulated annealing method. We compared the results obtained for 8 clinical cases using 5 intensity-modulated fields with those obtained using the two radiosurgery techniques. The comparison indexes are those defined by the Radiation Therapy Oncology Group (RTOG).
  
  
  RESULTS
  The results of this study demonstrated the advantages of using intensity modulation and the improvement obtained for the RTOG indexes in the case of CRT with MMLC, although the healthy peripheral tissues were less exposed to radiation with the radiosurgery techniques. The results also highlight the difficulty encountered with radiosurgery techniques in obtaining satisfactory dose homogeneity when the protocol is defined with numerous iosocenters.
  
  
  CONCLUSIONS
  In CRT with MMLC, intensity modulation makes it possible to reduce the number of fields used. It is especially useful to optimize the orientations in the case of target volumes of complex shape or when volumes at risk are in the vicinity of the target. If used correctly, MMLC can be a valuable alternative to conventional radiosurgery techniques.
authors.affiliation: Laboratoire de Biophysique, ITM, CHRU, Lille, France.
authors.forename: Carine
authors.initials: C
authors.lastname: Kulik
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Caudrelier
authors.forename: Maximilien
authors.initials: M
authors.lastname: Vermandel
authors.forename: Bernard
authors.initials: B
authors.lastname: Castelain
authors.forename: Salah
authors.initials: S
authors.lastname: Maouche
authors.forename: Jean
authors.initials: J
authors.lastname: Rousseau
mesh_terms: D000465:Algorithms; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008577:Meningeal Neoplasms / Q000532:radiotherapy / Q000601:surgery; D008579:Meningioma / Q000532:radiotherapy / Q000601:surgery; D015233:Models, Statistical; D010315:Particle Accelerators; D016634:Radiosurgery / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000295:instrumentation* / Q000379:methods*; D013696:Temperature