Disclosed herein too is a positron emission tomography calibration system comprising a positron emission tomography scanner having a ring detector that comprises at least one bin for receiving radiation a patient that is placed at approximately the center of the ring detector where the patient is irradiated with at least one dose of a treatment radiation beam a crystal efficiency calibration system that performs the following: measures activity generated by the at least one defined radiation dose in the at least one bin takes projection data of the measured activity calculates crystal efficiency from the projection data re-estimates the measured activity of each bin based on the calculated crystal efficiency and calibrates the detector based on the re-estimated measured activity.
