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Craniospinal Irradiation Using a Precise Geometric Matching Planning Technique with Dual Scattered Protons

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F Reynoso

F Reynoso*, T Zhao , B Sun , S Goddu , L Santanam , S Mutic , T Zhang , Washington University School of Medicine, St.louis, MO


SU-I-GPD-T-178 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Develop a precise geometric matching treatment planning technique for craniospinal irradiation.

Methods: Conventional craniospinal irradiation involves a field arrangement of posterior spinal fields (~1-3) and opposed lateral brain fields. Matching of the two divergent posterior spine-fields suffers from dose overlap anterior to the cord and dose under-dosing in the posterior aspect. This effect prompts the need to use multiple junction shifts to feather the dose in the match region to minimize dose uncertainties. The current precise geometric matching technique was developed using the Varian Eclipse Treatment Planning System (Varian Medical Systems, Inc.). The field arrangement is chosen to match beam divergence by rotating the gantry and couch. Analytical expressions based on the field aperture length were developed to obtain the gantry and couch angles. The snout position and compensator thickness were adjusted for dosimetric matching.

Results: The precise geometric matching of the treatment planning technique produced a homogeneous dose distribution throughout the entire target. The beam penumbra (~0.8 cm) of adjacent fields was matched resulting in uniform dose across fields within 3%.

Conclusion: A precise geometric matching technique was developed to accomplish improved dose uniformity for craniospinal irradiation using dual scattered protons. The technique enables robust delivery of uniform dose and simplifies the treatment planning process.

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