Oncology vault structure

A method of building a modular oncology vault structure, including the steps of:

• forming a foundation of cementitious material;
• placing a plurality of movable wall cells resting upon the foundation, each wall cell including an inside surface, an outside surface opposite the inside surface, and two lateral sides between the inside surface and the outside surface and opposite each other, the lateral sides having mating surfaces of non-planar complementary undulating shape with adjacent lateral surfaces of adjacent wall cells, said undulating shape including alternating crests and troughs that are flat and parallel with each other and offset by angled facets non-perpendicular to said troughs and non-perpendicular to said crests, the wall cells surrounding a majority of a perimeter of the vault;
• and
• covering a space inboard of the wall cells with a ceiling by stacking a plurality of ceiling slab elements resting upon said walls to form both a lower layer of ceiling slab elements and an upper layer of ceiling slab elements, with seams between adjacent said ceiling slab elements in said lower layer offset relative to seams between said ceiling slab elements in said upper layer.