A device for measuring radiation dosage is disclosed, comprising a flexible sheet, one or more detector assemblies disposed on the sheet, and detector retaining means for retaining the one or more detector assemblies on the sheet such that the one or more detector assemblies adopt the same curvature as the sheet when the sheet is deformed. Each one or more detector assembly comprises a plurality of beads threaded onto a fibre, the plurality of beads comprising radiation-sensitive material for recording information about a radiation dosage to which each bead is exposed, and the detector retaining means is configured to permit each one or more detector assembly to be subsequently detached from the sheet without removing the plurality of beads from the fibre. A method of detecting radiation dosage using the device is also disclosed.