The present invention relates to a sensor device for detecting dose of radiation received at the sensor device, the sensor device comprising a flexible body having a cross-section being comparatively small relative to the length of the device, a cladding at the flexible body, the cladding converting incoming radiation into visible light, and an optical shape sensing device disposed within the flexible body and configured to determine a shape of the flexible instrument relative to a reference, the shape sensing device configured to collect information based on its configuration to map an intraluminal structure during a procedure. The present invention further relates to a radiation therapy system including such a sensor device and a method of operating a radiation therapy system including such a sensor device.