Abstract: A phantom apparatus for measuring the radiation dose distribution produced by a brachytherapy device used to treat a localized area with radiation. The brachytherapy device includes an insertable probe capable of producing predefined radiation dose geometries about a predefined point. The phantom apparatus includes a tank containing a medium having a radiological equivalent characteristic of the localized area to be treated. The phantom apparatus also includes a radiation sensor for measuring the radiation dose and a positioning system for moving the probe with respect to the radiation sensor. The radiation sensor is also coupled to a positioning system to orient the sensor for optimal dose measurements. The phantom apparatus includes a control system that coordinates the movements of the probe and the radiation sensor to avoid a collision. The control system moves the probe along a predefined path around radiation sensor and records the dose at predefined points along the path.