A simulator possesses all the mechanical and geometrical features of which device?

The simulator is specifically designed to replicate the mechanical and geometrical features of an external beam treatment unit. This device is crucial in radiation therapy as it allows for the visualization and planning of treatment fields prior to actual patient treatment. By mimicking the setup of an external beam treatment unit, the simulator provides valuable information on how the radiation will be delivered, the positioning of the patient, and any necessary adjustments that can be made before starting the actual therapy.

In this context, the simulator includes features like collimators, gantries, and positioning mechanisms that are similar to those found in treatment devices. This allows the dosimetrist and the radiation oncologist to optimize the treatment plan for accuracy and efficacy.

The other devices mentioned, such as the linear accelerator or cobalt-60 machine, represent specific methods of delivering radiation but do not provide the simulated environment needed for treatment planning that the external beam treatment unit offers. Consequently, the simulator's primary purpose aligns closely with the functionality of external beam treatment units, justifying the choice.