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Dosimetric Effects Of Air Cavity Migration Through The Mammosite Multi-Lumen Balloon Treatments

W Li

W Li*, L Liu, A Shapiro, SUNY Upstate Medical Univ, Syracuse, NY

SU-E-T-347 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Study the dosimetric effects of air cavity migration through the mammosite multi-lumen balloon treatments.
Methods: Using Multi-lumen mammosite had the advantage of shaping the dose around the balloon to get better coverage and less skin dose/hot spots. However, when there was air pocket around the balloon, the air pocket tended to move/change volume throughout the treatment. Since the dose distribution was usually asymmetric in treatment plans, the effects of air pocket need to be studied.
Five(5) patients were selected for this study. For each patient, multi-lumen mammosite balloon was inserted into the cavity. Patient was then CTed and a treatment plan was created using Varian Eclipse TPS for delivery with Varian Varisource IX. PTV was created by expanding 1cm from balloon surface, 34 Gy were delivered in 10 fractions. The patient was CTed again after the last fraction before the balloon was extracted. The position of the balloon was checked to match the original CT. The treatment plan was recreated in the post-treatment CT.
In order to evaluate the true difference, a new PTV was created in both original CT and post-treatment CT. The new PTV was 1 cm expansion from the cavity, excluding the entrance pathway, since these tissues were intended to be treated. Coverage and hot spots were evaluated with the new PTVs.
Results: Through the treatment, air pocket normally will reduce volume and redistributed more evenly around the balloon, therefore coverage improved through the treatment. Since hot spots in multi-lumen cases were not symmetric, and during the planning, hot spots were usually targeted at air pocket if possible, at the end of the treatment, more tissue would receive high doses due to the air-pocket change.
Conclusion: Care needs to be taken when there is air-pocket in treatment planning using multi-lumen mammosite treatment, especially the hot spots.

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