M MacFarlane¹*, D Hoover² , E Wong³ , J Battista⁴ , J Chen⁵ , (1) University of Western Ontario, London, ON, (2) London Regional Cancer Program, London, ON, (3) London Regional Cancer Program, London, ON, (4) Western University, London, ON, (5) London Regional Cancer Centre, London, ON

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  M MacFarlane

(Sunday, 7/29/2018) 3:30 PM - 4:00 PM

Room: Exhibit Hall | Forum 4

Purpose: The goal of this work is to improve the plan optimization algorithm used in Unified Intensity-Modulated Arc Therapy (UIMAT) so that, in addition to generating hybrid VMAT-IMRT plans, UIMAT can also generate standalone VMAT or IMRT plans when optimal for the patient.

Methods: A proof-of-concept algorithm was developed in MATLAB. First, fluence map optimization and aperture sequencing is performed on equal-spaced beams within a user specified angular range. Then an accelerated proximal gradient method optimizes the aperture shapes and weights while simultaneously minimizing an l2-norm objective acting on the aperture weights. This objective forces the optimization algorithm to select the most impactful apertures in the plan, while eliminating the rest. From the remaining apertures, the algorithm can deduce the optimal mode of delivery (VMAT, IMRT, or mixed) for the patient. The algorithm finishes execution by sequencing the apertures into their VMAT and/or IMRT beams and performing a final direct aperture optimization.This new UIMAT algorithm was evaluated on three clinical test cases. The algorithm’s plans were compared with a dual 360° arc VMAT plan on a prostate and a head-and-neck case, and with a tangent-field IMRT plan on a breast case.

Results: In the prostate case, UIMAT also produced a dual-arc VMAT plan with similar tumor coverage but superior sparing of the organs at risk (OARs). A hybrid plan with a single 360° arc and 3 IMRT fields was generated in the head-and-neck case, which gave comparable tumor volume coverage and considerably better OAR sparing. In the breast case, UIMAT generated a hybrid plan with one partial 220° arc and two tangential IMRT fields. This plan slightly lowered the high-doses received by the adjacent liver and lung.

Conclusion: A new UIMAT algorithm was developed and demonstrated potential dosimetric benefits over standalone VMAT or IMRT.

Funding Support, Disclosures, and Conflict of Interest: This work was funded by the Canadian Institutes of Health Research as well as through a tri-partisan research agreement between the London Health Research Institute, Philips Healthcare, and the Government of Ontario.

Keywords

Not Applicable / None Entered.

Taxonomy

TH- External beam- photons: Development (new technology and techniques)

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