X-ray stray radiation dose levels in the therapy rooms of 6 medical electron linear accelerators working at 6

8 and 18 MV

respectively

have been measured using FARMER 2570/1A dosemeter and FJ 347A X γ dosemeter. The results show that the stray radiation doses at not less than 1 meter to the isocenter in the patient plane are not more than 0.1% of primary beam dose at the isocenter. The variation of stray radiation dose with the distance to the isocenter in the patient plane is found to follow the law of inverse square of the distance.The radiation dose evaluated with the inverse square distance law generally agrees with the measurement values within a factor of 2.