As an alternative to using an external probe to measure the whole body retention, a dual detector gamma camera system can be used. In this case the patient is scanned in the whole body mode in a reproducible geometry while lying supine on the imaging table. This method has been generally accepted for patient-specific whole body dosimetry of I-131 radiolabeled antibodies . Furthermore, it has been shown to yield comparable results with the external probe data . This technique has the following features: