Abstract: Systems and methods for low energy radiation x-ray radiation therapy system for use at a target within a cavity of a subject. In an aspect, the system uses an aperture shaping device used to shape the radiation beam from the low energy radiation source. In an aspect, the aperture shaping device includes a plurality of leaf assemblies which include leaves configured to form the aperture and engage the radiation beam. In an aspect, the present invention utilizes a geared mechanics approach to create an aperture using only one dial input. The design ensures that the field size of the collimator remains a constant shape as it is opened and closed. In an aspect, the overall size of the collimator may be scaled to accommodate various radiation therapy requirements.