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Modelling of the Magnetic Port in Temporary Breast Tissue Expanders for a Treatment Planning System

J Yoon

J Yoon*, D Heins , R Zhang , Louisiana State University, Baton Rouge, LA


SU-F-T-409 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To model the magnetic port in the temporary breast tissue expanders and to improve accuracy of dose calculation in Pinnacle, a commercial treatment planning system (TPS).

Methods: A magnetic port in the tissue expander was modeled with a radiological measurement-basis; we have determined the dimension and the density of the model by film images and ion chamber measurement under the magnetic port, respectively. The model was then evaluated for various field sizes and photon energies by comparing depth dose values calculated by TPS (using our new model) and ion chamber measurement in a water tank. Also, the model was further evaluated by using a simplified anthropomorphic phantom with realistic geometry by placing thermoluminescent dosimeters (TLD)s around the magnetic port. Dose perturbations in a real patient’s treatment plan from the new model and a current clinical model, which is based on the subjective contouring created by the dosimetrist, were also compared.

Results: Dose calculations based on our model showed less than 1% difference from ion chamber measurements for various field sizes and energies under the magnetic port when the magnetic port was placed parallel to the phantom surface. When it was placed perpendicular to the phantom surface, the maximum difference was 3.5%, while average differences were less than 3.1% for all cases. For the simplified anthropomorphic phantom, the calculated point doses agreed with TLD measurements within 5.2%. By comparing with the current model which is being used in clinic by TPS, it was found that current clinical model overestimates the effect from the magnetic port.

Conclusion: Our new model showed good agreement with measurement for all cases. It could potentially improve the accuracy of dose delivery to the breast cancer patients.

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