Medical particle irradiation apparatus

An irradiation room for particle beam therapy comprising:

• a first ring member located within and relatively rotatably supported by a rotating gantry carrying an irradiation unit emitting particle beams;
• a second ring member fixedly located opposite said first ring member;
• an anti-corotation unit moving in the direction of rotation of said rotating gantry as said rotating gantry rotates, said anti-corotation unit being in contact with both said first and second ring members to prevent said first ring member from rotating together with said rotating gantry during rotation of said rotating gantry;
• and
• a flexible moving floor located between said first and second ring members, said flexible moving floor being engaged with said first and second ring members in such a manner as to move freely such that its bottom is substantially level and that it moves as said rotating gantry rotates,
• wherein said anti-corotation unit comprises a first rotational element having an uneven portion which meshes with a first uneven portion formed on said first ring member, a second rotational element having an uneven portion which meshes with a second uneven portion formed on said second ring member, and a shaft member which couples said first and second rotational elements together, wherein said shaft member is attached to said rotating gantry such that said shaft member is free to rotate on its axis.