Impact of MLC properties and IMRT technique in meningioma and head-and-neck treatments.
OBJECTIVE
The impact of multileaf collimator (MLC) design and IMRT technique on plan quality and delivery improvements for head-and-neck and meningioma patients is compared in a planning study.


METHODS
Ten previously treated patients (5 head-and-neck, 5 meningioma) 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 patient. Consistent patient 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. PTV 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 1 Gy between the nine generated plans for each patient. Only larynx, parotids and eyes differ up to 1.5 Gy (Dmean or Dmax) or 7% (volume-constraint) due to (1) increased scatter, (2) not avoiding structures when using the full range of gantry rotation 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, PTV 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.


CONCLUSIONS
Fastest treatments with the best PTV 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.
Department of Radiation Oncology, Ludwig-Maximilians-University, Munich, Germany. Steffi.Kantz@med.uni-muenchen.de.
Steffi
S
Kantz
Department of Radiation Oncology, Ludwig-Maximilians-University, Munich, Germany. Matthias.Soehn@med.uni-muenchen.de.
Matthias
M
Söhn
Department of Radiation Oncology, Ludwig-Maximilians-University, Munich, Germany. Almut.Troeller@med.uni-muenchen.de.|Department of Radiation Oncology, William Beaumont Health System, Royal Oak, MI, USA. Almut.Troeller@med.uni-muenchen.de.
Almut
A
Troeller
Department of Radiation Oncology, Ludwig-Maximilians-University, Munich, Germany. Michael.Reiner@med.uni-muenchen.de.
Michael
M
Reiner
Department of Radiation Oncology, Ludwig-Maximilians-University, Munich, Germany. Helmut.Weingandt@med.uni-munenchen.de.
Helmut
H
Weingandt
Department of Clinical Medicine, Department of Oncology, Aarhus University, Aarhus, Denmark. malb@oncology.au.dk.
Markus
M
Alber
Department of Radiation Oncology, Ludwig-Maximilians-University, Munich, Germany. Claus.Belka@med.uni-muenchen.de.
Claus
C
Belka
Department of Radiation Oncology, Ludwig-Maximilians-University, Munich, Germany. Ute.Ganswindt@med.uni-muenchen.de.
Ute
U
Ganswindt
D002294:Carcinoma, Squamous Cell / Q000532:radiotherapy*; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008577:Meningeal Neoplasms / Q000532:radiotherapy*; D008579:Meningioma / Q000532:radiotherapy*; D058958:Organs at Risk; D010315:Particle Accelerators / Q000295:instrumentation; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D000077195:Squamous Cell Carcinoma of Head and Neck