In a shielded chamber for neutron therapy including a therapy room which has a main axis as determined by the direction of a high-energy neutron therapy beam surrounded by shielding and includes at one end a labyrinth entrance with at least two shielding wall sections displaced longitudinally along the main axis and extending into the room from opposite side walls, the wall sections include means for causing spallation of the incident high energy neutrons to thereby generate from the high energy neutrons in the high energy neutron beam a plurality of low energy neutrons which are then moderated.