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A Proton Pencil Beam Scanning Treatment Planning Technique for Breast Patients with Tissue Expanders Containing High Density Metallic Filling Ports

M Pankuch

M Pankuch*, S Gans , D Kaplan , M Stauffer , S Niles , S Boyer , D Hecksel , B Kreydick , S Laub , A Panchal , H Ramirez , S Schmidt , W Hartsell , C Kesslering , M Gao , CDH Proton Center, Warrenville, IL


SU-I-GPD-T-176 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To develop treatment planning method using Intensity Modulated Proton Therapy (IMPT) that delivers the prescribed doses to target tissues in the presence of a breast expander containing a high density metallic filling port. Due to the challenges in the accuracy of calculating proton scattering and proton path lengths through a high density filling port, this method eliminates all proton spots that have a potential to pass through the port.

Methods: PBS plans were made for 7 Stage III Breast patients (2 Right Sided, 5 Lt Sided). Two fields were used with constraints that omitted all spots downstream of the defined metallic port. Spot weights were determined using a multi field iterative optimization to deliver a cumulative uniform dose to the target regions around the port. Gantry angles are chosen to allow the target shadowed by any one field to be supplemented by doses delivered by the complementary field. To minimize the sensitivities to set-up errors and range uncertainty, regions superior and inferior to the metallic filling port were optimized using Single Field Optimization methods. This segregation of optimization areas was used to increase overall plan robustness.

Results: Plans have been developed that demonstrate appropriate target coverage. For all plans the average V20Gy(RBE) and V5Gy(RBE) of the ipsilateral lung was 17.2Gy(RBE) and 32.8Gy(RBE) respectively. Mean heart dose of the Lt sided patients was 1.8Gy(RBE) with and average V5Gy(RBE) of 8%. The average hot spot, D(1cc) for all plans was 106% and no plans had any volume receiving >110%. Robustness evaluations using 3mm set-up and 3.5% range error demonstrated V95% of >95% for the CTV.

Conclusion: An IMPT planning method to treat breast targets around a metal filling port has been developed. This method produced clinically acceptable plans while eliminating inaccuracies for calculations of particles passing through the metallic port.

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