Phase II Multi-center Trial Evaluating 5 Fraction Stereotactic Partial Breast Irradiation Using Gammapod

The GammaPod is a new external beam radiotherapy device dedicated for stereotactic radiotherapy of breast cancer (Xcision Medical Systems, LLC, Columbia, Maryland). The design goal of the GammaPod has been the ability to deliver ablative doses with sharp gradients under stereotactic image guidance. Highly focused radiation is achieved at the isocenter due to the cross-firing from 36 radiation arcs generated by rotating 36 individual Cobalt-60 beams.In order to immobilize the breast during imaging and treatment and in order to get a stereotactic localization of the breast target volume, a vacuum-assisted breast immobilization cup with built-in stereotactic frame is used. The patient can be imaged on a CT or MRI wearing the vacuum-assisted breast cup and then be transferred to the GammaPod for treatment. Then, the planner is required to delineate the gross tumor volume (GTV) and its subclinical extensions. Multiple targets within a breast are allowed.Different doses can be prescribed to different targets.One benefit of using the GammaPod over the cyberknife for breast SBRT, is elimination of the need for internal gold fiducial markers, which are required for the cyberknife treatment. Using a stereotactic technique for APBI allows smaller margins in comparison to a 3DCRT technique. The total expansions on the RAPID trial (3DCRT APBI) were 1.0 cm CTV expansion on the lumpectomy cavity and an additional 1.0 cm for PTV, for a total expansion of 2.0 cm. As a 3DCRT technique was used on the RAPID trial limited number of radiation beams were employed, no Intensity Modulated Radiation Techniques allowed, and the margins used to create a PTV were relatively large (total margin 2 cm). As the GammaPod will allow us to minimize the volume of normal breast being irradiated, and decrease the PTV volume we hypothesize that a stereotactic technique with the GammaPod will allow us to improve on the 3 year global cosmesis rates (physician and patient) reported in the RAPID trial (3DCRT) by 40% despite 5 daily fractions of SBRT (in contrast to 38.5Gy/10 fractions 3DCRT BID on the RAPID trial) The GammaPod was FDA approved 12-2017.