A phase 1 trial of preoperative partial breast radiation therapy: Patient selection, target delineation, and dose delivery.

Abstract Purpose Diffusion of accelerated partial breast irradiation into clinical practice is limited by the need for specialized equipment and training. The accessible external beam technique yields unacceptable complication rates, likely from large postoperative target volumes. We designed a phase 1 trial evaluating preoperative radiation therapy to the intact tumor using widely available technology. Methods and materials Patients received 15, 18, or 21 Gy in a single fraction to the breast tumor plus margin. Magnetic resonance imaging (MRI) was used in conjunction with standard computed tomography (CT)-based planning to identify contrast enhancing tumor. Skin markers and an intratumor biopsy marker were used for verification during treatment. Results MRI imaging was critical for target delineation because not all breast tumors were reliably identified on CT scan. Breast shape differences were consistently seen between CT and MRI but did not impede image registration or tumor identification. Target volumes were markedly smaller than historical postoperative volumes, and normal tissue constraints were easily met. A biopsy marker within the breast proved sufficient for setup localization. Conclusions This single fraction linear accelerator–based partial breast irradiation approach can be easily incorporated at most treatment centers. In vivo targeting may improve accuracy and can reduce the dose to normal tissues.