Briefly stated, the present invention discloses a novel device that automatically calibrates and adjusts the intensity, dosage, and other parameters of a radiation delivery system and radiation source based on selected or detected radiation delivery systems. Such radiation delivery systems include optical fiber systems, and any type of diffuser, as well as bare fiber tips. The functions of a radiation source and a calibration device are combined by storing the characteristics of a wide variety of delivery system types and brands and calibrating the radiation based on those stored characteristics. In a preferred embodiment, a calibration sheath is provided that fits over a delivery system, such as a bare fiber tip or a diffuser at the distal end of a fiber, to both protect the system during calibration and direct output radiation to a detector. In another embodiment, one or more detectors are situated on the interior surface of the calibration sheath to directly measure at least a preselected portion of the emitted radiation. Power readings are directed to a calibration subsystem from the detector or detectors, which then adjusts the emitted power to conform to desired treatment parameters. The need for different calibration devices based on the characteristics of the delivery system is alleviated.