Determination of TG-43 Parameters for the Xoft Cervical Applicator

Graduate Investigator: Samantha Simiele

Summary of Research: The current dosimetry calculation formalism for brachytherapy treatment planning utilizes the AAPM TG-43 protocol. The TG-43 formalism involves the superposition of pre-calculated dose distributions onto computed tomography scans of the patient. These dose distributions are determined using tabulated Monte Carlo values and measurements performed in a homogeneous water phantom with full backscatter. Therefore, treatment planning by superposition of these dose distributions on patient geometries does not account for finite patient dimensions and tissue inhomogeneities. Further, when applicators are used as part of the treatment plan (such as the treatment of cervical cancer) the materials and geometric characteristics of the applicator are ignored. This can result in an over or underestimation of dose delivered to a lesion or avoidance structure, compromising the effectiveness of the therapy. To address this issue, Xoft’s new cervical applicator is being directly incorporated into TG-43 parameters through measurements with the applicator present. The air kerma strength, dose rate constant, radial dose function, and azimuthal anisotropy values will be determined based on methods developed by Dr. Tina Pike.