title: Intensity-modulated radiotherapy of breast cancer using direct aperture optimization.
abstract: OBJECTIVE
  To design a clinically reliable and efficient step-and-shoot IMRT delivery technique for the treatment of breast cancer using direct aperture optimization (DAO). Using DAO, segments are created and optimized within the same optimization process.
  
  
  METHODS
  The DAO technique implemented in the Pinnacle treatment planning system, which is called direct machine parameter optimization (DMPO), was used to generate IMRT plans for twelve breast cancer patients. The prescribed dose was 50 Gy. Two DMPO plans were generated. The first approach uses DMPO only; the second technique combines DMPO with two predefined segments (DMPO(segm)), having shapes identical to the conventional tangential fields. The weight of these predefined segments is optimized simultaneously with DMPO. The DMPO plans were compared with normal two-step (TS) IMRT, creating segments after optimizing the intensity.
  
  
  RESULTS
  Dose homogeneity within the target volume was 4.8+/-0.6, 4.3+/-0.5 and 3.8+/-0.5 Gy for the TS, DMPO and DMPO(segm) plans, respectively. Comparing the IMRT plans with an idealized dose distribution obtained using only beamlet optimization, the degradation of the dose distribution was less for the DMPO plans compared with the two-step IMRT approach. Furthermore, this degradation was similar for all patients, while for the two-step IMRT approach it was patient specific.
  
  
  CONCLUSIONS
  An efficient step-and-shoot IMRT solution was developed for the treatment of breast cancer using DMPO combined with two predefined segments.
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute, Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
authors.forename: Bram
authors.initials: B
authors.lastname: van Asselen
authors.forename: Marco
authors.initials: M
authors.lastname: Schwarz
authors.forename: Corine
authors.initials: C
authors.lastname: van Vliet-Vroegindeweij
authors.forename: Joos V
authors.initials: JV
authors.lastname: Lebesque
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Mijnheer
authors.forename: Eugene M F
authors.initials: EM
authors.lastname: Damen
mesh_terms: D000465:Algorithms; D001943:Breast Neoplasms / Q000532:radiotherapy*; D006801:Humans; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods*