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Dosimetric Advantage of IMRT Compared to VMAT for H&N Plans Using a Prototype Jawless and Fast MLC System

D Mihailidis

D Mihailidis*, R Scheuermann , S Anamalayil , C Kennedy , L Brady , L Dong , J Metz , University of Pennsylvania, Philadelphia, PA


SU-I-GPD-T-505 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To study the dosimetric performance of novel a jawless MLC collimating system with a high leaf speed capability of 5 cm/sec, intended for faster intensity modulated deliveries (IMRT/VMAT).

Methods: A new MLC system with 56 leaves of 1cm width (28x28cm2 maximum field size at 100cm), is mounted on a straight-through linac that produced a single 6X-FFF beam. The flexibility of this prototype MLC system is due to the absence of jaws, maximum leaf over-travel and 100% inter-digitization and leaf speed of 5cm/s. A group of H&N plans were performed with IMRT and VMAT deliveries with intention to study the dosimetric feasibility for the prototype system, look for dosimetric differences due to its jawless nature, leaf width and, due to its 100% over-travel and inter-digitization capability. Dose distributions and DVHs for IMRT and VMAT plans were compared as means of plan evaluation.

Results: Preliminary results of the dosimetric comparison between IMRT and VMAT deliveries with the prototype MLC system showed that both techniques met the prescription goals with the IMRT plans having superior target dose homogeneity and clinically significantly lower mean doses for the organs-at-risk (OARs). However, an interesting reduced dose conformality was observed superiorly for the IMRT delivery that was independent of the collimator angle.

Conclusion: The prototype fast jawless MLC system with a straight-through 6X-FFF linac delivers more conformal plans for IMRT than VMAT for H&N. The dosimetric performance of jawless MLC systems increases the importance of lower leaf transmission and is influenced by the lack of standard jaws. Further investigation is under way for other treatment sites.

Funding Support, Disclosures, and Conflict of Interest: This work was performed as part of a research agreement with Varian Medical Systems.

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