Abstract: The paper presents 6 MeV sealed--off side--coupled standing wave accelerating tubes with the gridcontrolled electron guns. The gun anode voltage is 8 kV DC. The total length of the accelerating tubesis only 0.33 m. High output X--rays with dose rate up to 6.4 Gy/min at 1 meter from target can beobtained by the tubes when a 2.6 MW, 4.2μs, 280 Hz pulse magnetron is used as RF power source.The beam spot diameter is less than 2 mm.