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Dosimetric Characterization and Comparison of the Elekta Agility and MLCi2 Multi-Leaf Collimator Heads


D Cutright

D Cutright*, M Gopalakrishnan, V Sathiaseelan, Robert H. Lurie Comprehensive Cancer Center & Department of Radiation Oncology, Northwestern University, Northwestern Memorial Hospital, Chicago, IL 60611

SU-E-T-261 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
The new Elekta Agility™ radiation head with integrated 160 x 5mm inter-digitating tungsten-alloy leaves has been designed with leaf sides tilted to reduce overall transmission and leaf leakage. In this study, a comparison of the major dosimetric parameters of the Elekta Agility™ 160 leaf (5mm leaf width) multi-leaf collimator (MLC) head design and the older Elekta MLCi2™ 80 leaf MLC head (10mm leaf width) is presented.

Methods:
Electron and photon beam data (including PDDs and profiles for various field sizes) were collected and analyzed using IBA hardware and software products for linac commissioning (i.e., IBA water tank, diodes, and OmniPro Accept™ 7). MLC transmission and leakage was measured using gafchromic film and SunNuclear MAPcheck2™.

Results:
Photon beams: Percent depth doses for 6MV and 10MV photon beams with various field sizes indicated little difference between the MLCi2™ and Agility™ heads (i.e., less than 1% difference at depths beyond dmax). Penumbra and umbra of dose profiles matched well for both energies; marginally differences were noticed on the toe-side of large wedged-fields. The average Agility™ MLC transmission was measured to be 0.4%, nearly an order of magnitude lower than the MLCi2™. Collimator scatter factors were nearly identical for small fields and reduced by as much as 1% for larger fields.
Electron beams: PDDs of electron beam energies of 6, 9, 12, 15, and 18 MeV were collected, indicating little differences between the Elekta Infinity™ with the MLCi2™ and Agility™ heads.

Conclusion:
Analysis of the MLCi2™ and Agility™ beam data indicate little to no undesirable dosimetric differences; the largest deviation being a significant decrease in MLC transmission and leakage. These characteristics, combined with a significant increase in leaf speed, make the Elekta Agility™ a considerable improvement over the MLCi2™.

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