The gyrotron system for ECH and burn control on ITER requires at least 50MW of RF power at frequencies near 170GHz operating in CW. To meet these requirements, high efficiency gyrotron tubes with greater than or equal to 1MW power output capability are necessary, as well as simple coupling to either a quasi-optical or waveguide transmission line. The paper reports the feasibility study on the design of an ITER-relevant gyrotron oscillator at 170GHz, 1MW CW employing a diode electron gun, an advanced internal quasi-optical converter, a cryogenically cooled single disk sapphire window, and a depressed potential collector. The operating mode selection and the cavity design is a compromise between many design constraints.