Evaluation Of Change In The Lumpectomy Cavity During Radiation Therapy By Weekly Ultrasound And By Daily Ultrasound Localization During The Radiation Boost Dose

This study aims to determine whether and to what extent the lumpectomy volume changes during a course of external beam radiation for breast conservation therapy. The highest risk area for relapse following breast conservation is at or near the index lesion. Therefore accurate definition of this volume is important for treatment planning. In newer techniques of conformal breast irradiation, the lumpectomy cavity defines the gross tumor volume, and accurate definition is critical to target coverage. This study determines the change in volume of the lumpectomy cavity using weekly ultrasound measurements during a course of whole breast radiation therapy. Daily ultrasound localization during the boost treatment was performed to determine if the CT- based boost fields accurately targets the lumpectomy site. Patients receiving post lumpectomy radiation therapy of the intact whole breast were enrolled in an IRB-approved protocol to evaluate lumpectomy volume changes during the course of external beam radiation. Ultrasound imaging of the lumpectomy cavity was performed on the first day of treatment, and weekly thereafter. Measurements of the lumpectomy cavity diameters on a pair of orthogonal ultrasound images were used to estimate the lumpectomy volume assuming an ellipsoidal cavity. These weekly volume estimates were used to determine the percent volume change over the course of therapy. Daily ultrasound localization at the time of the lumpectomy site boost was performed to determine the shift in position from the clinical setup recommended by aligning the ultrasound imaged cavity with the in room CT-coordinates. Total displacements of the recommended shifts were determined as a measure of the lumpectomy site targeting accuracy. A complete set of measurements for 5 patients who enrolled in and completed the IRB approved protocol have been analyzed. Eighty percent (4/5) were found to have an ultrasound volume decrease of at least 50% over the course of therapy. The average time to experience a volume change decrease to 60% was 3 weeks (+/− 1 week). The ultrasound-estimated volumes were 1.5 to 3 times smaller than the CT lumpectomy cavity volumes. The initial daily ultrasound localization measurements were inconclusive (average displacement greater than the deviation) and lead to a revised procedure for setting up to the lumpectomy site from the CT-based coordinates. Weekly ultrasound measurements demonstrate the lumpectomy site changes significantly in volume during a course of external bean radiation therapy. Treatment accuracy may be increased by localizing the target, monitoring volume changes, and re-imaging the target prior to boost radiation.