Impact of MLC properties and IMRT technique in XXXX and head-and-neck treatments.

@entity1 @entity717 @entity1653 @entity343
PURPOSE: The impact of multileaf collimator (MLC) design and IMRT technique on plan quality and delivery improvements for head-and-neck and @entity1653 @entity1 is compared in a planning study. MATERIAL AND METHODS: Ten previously treated @entity1 (5 head-and-neck, 5 @entity1653 ) were re-planned for step-and-shoot IMRT (ssIMRT), sliding window IMRT (dMLC) and VMAT using the MLCi2 without (-) and with (+) interdigitation and the Agility-MLC attached to an Elekta 6MV linac. This results in nine plans per @entity1 . Consistent @entity1 individual optimization parameters are used. Plans are generated using the research tool Hyperion V2.4 (equivalent to Elekta Monaco 3.2) with hard constraints for critical structures and objectives for target structures. For VMAT plans, the improved segment shape optimization is used. Critical structures are evaluated based on QUANTEC criteria. @entity343 coverage is compared by EUD, Dmean, homogeneity and conformity. Additionally, MU/plan, treatment times and number of segments are evaluated. RESULTS: As constrained optimization is used, all plans fulfill the hard constraints. Doses to critical structures do not differ more than 1Gy between the nine generated plans for each @entity1 . Only larynx, parotids and eyes differ up to 1.5Gy (Dmean or Dmax) or 7  % (volume-constraint) due to (1) increased scatter, (2) not avoiding structures when using the full range of @entity717 and (3) improved leaf sequencing with advanced segment shape optimization for VMAT plans. EUD, Dmean, homogeneity and conformity are improved using the Agility-MLC. However, @entity343 coverage is more affected by technique. MU increase with the use of dMLC and VMAT, while the MU are reduced by using the Agility-MLC. Fastest treatments are always achieved using Agility-MLC, especially in combination with VMAT. CONCLUSION: Fastest treatments with the best @entity343 coverage are found for VMAT plans with Agility-MLC, achieving the same sparing of healthy tissue compared to the other combinations of ssIMRT, dMLC and VMAT with either MLCi2(-/+) or Agility.
