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Isodose Curve Manipulation for Interactive Dose Shaping

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C Kamerling

C Kamerling*, P Ziegenhein, H Heinrich, U Oelfke, German Cancer Research Center (DKFZ), Heidelberg, Germany

TH-A-213AB-2 Thursday 8:00:00 AM - 9:55:00 AM Room: 213AB

Purpose:
The interactive dose shaping (IDS) planning paradigm aims to perform interactive local dose adaptations of an IMRT plan without compromising already established valuable dose features in real-time. In this work we introduce an interactive isodose curve manipulation tool which enables local modifications of a dose distribution by intuitively dragging an isodose curve.

Methods:
We developed an in-house IMRT TPS framework consisting of a 3D GUI for dose manipulation and visualization. Dose calculations are performed with an adapted pencil beam algorithm, enabling ultra-fast dose calculation for local fluence map changes. Starting point of our planning approach is a homogeneous, conformal dose of the target volume at the prescribed dose level.
This initial dose distribution will be interactively modified by our isodose curve manipulation tool, which induces a dose modification as a direct change of dose in one or more voxels. This modification is incrementally obtained by fluence adjustments. These will naturally lead to unintended and unwanted dose features outside the vicinity of modified dose. A subsequent recovery step identifies these voxels and aims to recover their original dose by selecting and modifying an orthogonal set of fluence amplitudes that does not alter the initially achieved dose modification.

Results:
We evaluated the proposed tool by adapting the dose distribution of a prostate case (9 beams, coplanar). The initial homogeneous, conformal dose distribution led to a severe over dosage of the rectum. By manipulation of isodose curves it was possible to reduce the dose in the rectum to clinically acceptable values. Dose modification for one dragged point on the isodose curve took about 1 second, subsequent recovery of 25 points took 2 seconds. This time includes approximately 300 local fluence updates per beam as well as 300 dose calculations.

Conclusions:
We proposed, implemented and successfully tested an isodose curve manipulation tool.

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