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Inverse Planning for 3D Intensity-Modulated Grid-Therapy

J Chen

J Chen*, D Rashid, E Yu, H Fakir, S Karnas, K Jordan, London Health Science Center, London, ON

TH-A-213AB-3 Thursday 8:00:00 AM - 9:55:00 AM Room: 213AB

Purpose: To develop an inverse optimization method for 3D intensity-modulated grid-therapy to improve dose distribution of grid therapy of advanced stage tumors.

Methods: The following process was used to generate a 3D intensity-modulated grid-therapy plan. First, based on the geometry of the target volume and organs at risk (OAR), three to six radiation fields were selected to minimize the overlap between the target volume and OARs. Typically, three orthogonal fields were used to minimize the overlap between the fields to maintain grid-like dose distribution for each field. Second, a step-and-shoot IMRT plan was generated with selected fields using Pinnacle treatment planning system (Philips Medical Systems). Third, each MLC segment was converted to a grid field defined by additional MLC segments using an in-house developed program. Finally, the plan was further optimized using segment weight optimization in Pinnacle treatment planning system, maintaining the grid shape for each IMRT field with optimized intensities for the opening grids. The method was tested for a few clinical cases with bulky tumors. Dose distributions and dose volume histograms were compared between conventional single-field grid-therapy plan and 3D intensity-modulated grid-therapy plan.

Results: Compared to conventional single-field grid-therapy plan, 3D intensity-modulated grid-therapy plan gives higher minimum dose to the target volume for potential improved tumor control probability and lower space-fractionated doses to OARs for potential reduction of normal tissue complication probability. The drawback of the method is longer radiation treatment time.

Conclusions: A method was developed to generate 3D intensity-modulated grid-therapy plan. Comparing to single-field grid-therapy plan, it gives higher dose to the target volume and lower space-fractionated dose to OARs for a potential therapeutic advantage.

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