A radiation detecting cassette has a casing including a first flat plate for facing a patient and a second flat panel for facing a surgical table. The first flat plate and the second flat panel are spaced from each other by a predetermined distance. The casing also includes a pair of first and second tapered side members disposed on respective side edges of the first and second flat plates. The first and second tapered side members are progressively tapered toward their distal ends. The first and second tapered side members house therein respective radiation shields, which in turn house therein a battery, a cassette controller, and a transceiver.