A radiation shielding structure or vault includes an outer wall and an inner wall. The outer wall includes at least one outer wall panel formed into a cylinder shape having an outer wall opening. The inner wall includes at least one inner wall panel formed into a cylinder shape having an inner wall opening aligned with the outer wall opening. Tie rods secure the inner wall to the outer wall to support and hold the spacing between the walls. A tunnel structure is inside the inner wall opening and the outer wall opening. A radiation shielding door is coupled to the tunnel structure. A radiation shielding filler material is disposed in between the outer wall and the inner wall.