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Objective: In order to improve the convenience and reliability of the calibration procedure with respect to the quantitative aspects of PET scanners, we have been developing new methods that rely on the use of point-like radioactive sources. The aim of this study is to report the results of the application of the proposed method for obtaining the cross-calibration factors (CCFs) of a clinical PET scanner for the first time. Methods: A 22Na point-like source was moved in the axial direction to cover the axial field-of-view (FOV) of a commercial PET scanner, SET-2400W (Shimadzu). From reconstructed images, saturated regions-of-interest (ROI) values were used to calculate the CCFs that were defined slice by slice. Results: It was possible to obtain CCFs that were practically equivalent to those obtained by the standard method with cylindrical water phantoms. The variations in the CCFs obtained over about a half-year were well reproduced by the proposed method. Conclusion: The proposed calibration method, which is based on the use of a point-like radioactive source, is useful for determining CCFs and their variations for a clinical PET scanner.