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An online replanning method using warm start optimization and aperture morphing for flattening-filter-free beams
Ergun E Ahunbay1, O Ates1, X A Li1
1Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226.
Medical Physics
|August 5, 2016
Summary
A new automated method combines two-step plan interpolation and segment aperture morphing (SAM) to correct for flattening-filter-free (FFF) beam translational dose effects and target deformation in intensity-modulated radiation therapy.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Planning
Background:
- Patient positioning adjustments like couch shifts are often restricted in advanced radiotherapy, particularly with MR-linacs.
- Existing segment aperture morphing (SAM) methods can correct for target deformation but introduce adverse translational dose effects with flattening-filter-free (FFF) beams.
- Accurate dose delivery in intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) requires addressing both target motion and beam characteristics.
Purpose of the Study:
- To develop and evaluate a novel two-step automated replanning method to compensate for translational dose effects specific to FFF beams.
- To integrate this method with segment aperture morphing (SAM) to simultaneously correct for target deformation in IMRT/VMAT.
- To provide an efficient and automated solution for adaptive radiotherapy when couch shifts are not feasible.
Main Methods:
- An offline step generates a series of preshifted plans (PSPs) using a 'warm start' optimization to preserve segment shapes.
- An online step selects or interpolates the closest PSP based on daily imaging to account for translational shifts.
- The previously established SAM algorithm is applied for daily target deformation correction, with the entire process automated and near-instantaneous.
Main Results:
- The two-step interpolation effectively mitigates the translational dose effects associated with FFF beams.
- Combined with SAM, the method accurately corrects for target deformation, demonstrating efficacy in sample prostate and pancreas cases.
- The automated process achieves results comparable in time (5-10 min) to existing SAM methods, potentially reducing the need for numerous PSPs.
Conclusions:
- The proposed two-step automated method, coupled with SAM, successfully addresses both FFF beam translational effects and target deformation.
- This approach offers a fully automated solution for adaptive radiotherapy, requiring only target contour delineation for SAM.
- The method enhances the feasibility of advanced radiotherapy techniques where couch shifts are prohibited or undesirable.
