title: To evaluate the accuracy of dynamic versus static IMRT delivery using portal dosimetry.
abstract: BACKGROUND
  To evaluate the delivery accuracy of dynamic (DMLC) and static (SMLC) intensity modulated radiation therapy (IMRT) techniques using portal dosimetry (PD) in Varian Eclipse Treatment Planning System.
  
  
  METHODS
  Seven DMLC IMRT Head and Neck plans were retrospectively generated for the study using SMLC mode at 20, 10 and 5 levels of intensity (SMLC20, SMLC10, SMLC5). Dosimetric verifications performed by PD on a total of 107 fields were evaluated using the gamma index (maximum (γmax), average (γavg), percentage of points with (γ%) ≤ 1). The images were acquired at a source-detector distance of 100 cm at gantry zero degree and also at clinically planned gantry angles.
  
  
  RESULTS
  For both modes, measurements are within acceptable criteria. (γ%) ≤ 1 improves by increasing SMLC levels (+3.4 % from SMLC5 to SMLC20, p < 0.001) and using DMLC (+3.9 % and +0.6 % compared to SMLC5 and SMLC20, respectively, p < 0.001). Also (γmax) parameter improves significantly by increasing SMLC levels (+22 % from SMLC5 to SMLC20) and using DMLC (+34 % and +16 % compared to SMLC5 and SMLC20, respectively). The effect of the gantry rotation influences the delivery accuracy by up to -7 % (p < 0.05). The effect of leaves travelling direction was almost negligible (1 %).
  
  
  CONCLUSIONS
  A good agreement between calculated and measured fluences was obtained for DMLC and SMLC techniques at higher intensity levels; however, DMLC delivery ensures the best reproduction of computed fluence maps. The gantry rotation influences the delivery accuracy in particular for SMLC modes at lower intensity levels.
authors.affiliation: Department of Radiation Oncology, IRCCS CROB, 1 Padre Pio Street, 85028, Rionero in Vulture, PZ, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Clemente
authors.forename: R
authors.initials: R
authors.lastname: Caivano
authors.forename: M
authors.initials: M
authors.lastname: Cozzolino
authors.forename: G
authors.initials: G
authors.lastname: Califano
authors.forename: C
authors.initials: C
authors.lastname: Chiumento
authors.forename: A
authors.initials: A
authors.lastname: Fiorentino
authors.forename: V
authors.initials: V
authors.lastname: Fusco
mesh_terms: D006801:Humans; D058958:Organs at Risk; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation / Q000379:methods / Q000592:standards; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000379:methods; D012189:Retrospective Studies; D012680:Sensitivity and Specificity