Abstract
PURPOSE: This paper introduces a new external beam radiotherapy device named GammaPod that is dedicated for stereotactic radiotherapy of breast cancer. METHODS: The design goal of the GammaPod as a dedicated system for treating breast cancer is the ability to deliver ablative doses with sharp gradients under stereotactic image guidance. Stereotactic localization of the breast is achieved by a vacuum-assisted breast immobilization cup with built-in stereotactic frame. 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. The dedicated treatment planning system optimizes an optimal path of the focal spot using an optimization algorithm borrowed from computational geometry such that the target can be covered by 90%-95% of the prescription dose and the doses to surrounding tissues are minimized. The treatment plan is intended to be delivered with continuous motion of the treatment couch. In this paper the authors described in detail the gamma radiation unit, stereotactic localization of the breast, and the treatment planning system of the GammaPod system. RESULTS: A prototype GammaPod system was installed at University of Maryland Medical Center and has gone through a thorough functional, geometric, and dosimetric testing. The mechanical and functional performances of the system all meet the functional specifications. CONCLUSIONS: An image-guided breast stereotactic radiotherapy device, named GammaPod, has been developed to deliver highly focused and localized doses to a target in the breast under stereotactic image guidance. It is envisioned that the GammaPod technology has the potential to significantly shorten radiation treatments and even eliminate surgery by ablating the tumor and sterilizing the tumor bed simultaneously.