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Implementation of An Online Replanning Tool for VMAT Using Flattening Filter-Free Beams

O Ates

O Ates*, E Ahunbay , X Li , Medical College of Wisconsin, Milwaukee, WI


SU-E-J-127 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: This is to report the implementation of an online replanning tool based on segment aperture morphing (SAM) for VMAT with flattening filter free (FFF) beams.

Methods: Previously reported SAM algorithm modified to accommodate VMAT with FFF beams was implemented in a tool that was interfaced with a treatment planning system (Monaco, Elekta). The tool allows (1) to output the beam parameters of the original VMAT plan from Monaco, and (2) to input the apertures generated from the SAM algorithm into Monaco for the dose calculation on daily CT/CBCT/MRI in the following steps:

(1) Quickly generating target contour based on the image of the day, using an auto-segmentation tool (ADMIRE, Elekta) with manual editing if necessary;

(2) Morphing apertures based on the SAM in the original VMAT plan to account for the interfractional change of the target from the planning to the daily images;

(3) Calculating dose distribution for new apertures with the same numbers of MU as in the original plan;

(4) Transferring the new plan into a record & verify system (MOSAIQ, Elekta);

(5) Performing a pre-delivery QA based on software;

(6) Delivering the adaptive plan for the fraction.

This workflow was implemented on a 16-CPU (2.6 GHz dual-core) hardware with GPU and was tested for sample cases of prostate, pancreas and lung tumors.

Results: The online replanning process can be completed within 10 minutes. The adaptive plans generally have improved the plan quality when compared to the IGRT repositioning plans. The adaptive plans with FFF beams have better normal tissue sparing as compared with those of FF beams.

Conclusion: The online replanning tool based on SAM can quickly generate adaptive VMAT plans using FFF beams with improved plan quality than those from the IGRT repositioning plans based on daily CT/CBCT/MRI and can be used clinically.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by Elekta Inc. (Crawley, UK).

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