Namratta Sehgal with Professor Bruce Thomadsen and Dan McDonald

UW-Madison Department of Medical Physics

As breast cancer has become more prevalent in the past years, new treatments have been developed. While external beam therapy is a common treatment plan for many patients, high dose-rate brachytherapy can be used for limited types of breast cancer. This involves the placement of radioactive sources within the breast to treat the surrounding tissue. Two such treatments include multi-catheter interstitial implants and single balloon-catheter intracavitary insertions. Both of these may be used to achieve similar results. Intracavitary treatment, however, can be affected by trapping air pockets on the surface of the balloon during implantation, which then pushes tissue outside the desirable irradiation margin. In order to determine if these air pockets are large enough to significantly affect the delivered dose, we used the Equivalent Uniform Dose- or EUD. In treatment plans with non-uniform dose distribution, EUD is used to find the uniform dose throughout the volume that would give the equivalent therapeutic effect. An experiment was performed to investigate the actual tissue displacement due to air pockets. By combining this information and then comparing the EUD of treatment without an air pocket to the EUD of treatment with an air pocket of known radius, we were able to find that generally, air pockets do not deleteriously impact the treatment and radiation received.