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Dosimetric Consequences From Minimal Displacements in APBI with SAVI Applicators

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S Chandrasekara

S Chandrasekara1*, N Dumitru2 , M Hyvarinen3 , S Pella4 , (1) ,,,(2) ,Bucharest, ,(3) Florida Atlantic University, Boca Raton, FL, (4) South Florida Radiation Oncology, Boca Raton, FL


SU-E-J-167 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

To determine the importance of providing proper solid immobilization in every fraction of treatment in APBI with brachytherapy.

125 patients treated with APBI brachytherapy with SAVI applicators at SFRO Boca Raton, from 2013-2015 were considered for this retrospective study. The CT scans of each patient, which were taken before each treatment, were imported in to the Oncentra treatment planning system. Then they were compared with the initial CT scan which was used for the initial plan. Deviation in displacements in reference to ribs and skin surface was measured and dosimetric evaluations respective to the initial image were performed.

Small deviations in displacements were observed from the SAVI applicator to the ribs and the skin surface. Dosimetric evaluations revealed, very small changes in the inter-fractionation position make significant differences in the maximum dose to critical organs. Additionally, the volume of the cavity also changed between fractions. As a result, the maximum dose manifested variance between 10% and 32% in ribs and skin surface respectively.

It appears that taking a CT scan before each treatment is necessary to minimize the risk of delivering undesired high doses to the critical organs. This study indicates, in 30% of the cases re-planning was necessary between treatments. We conclude that, treatment planning teams should evaluate the placement of the device by analyzing the CT images before each treatment and they must be prepared for re-planning if needed. This study also reveals the urgent need of improving the immobilization methods with APBI when treating with the SAVI applicator.

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