The application of a digital whole body scanner to the dosimetry of intralymphatic 32P/131I Lipiodol.

A quantitative, digital-output, whole-body scanner in a low background area has been used in the dosimetry of 32P/131I Lipiodol for intralymphatic radiotherapy. Five patients with malignant melanoma received intralymphatic administrations of Lipiodol labelled with 6 mCi 32P and 1.5 mCi 131I. The 131I is used primarily as a tracer for external measurements and the 32P as the chief therapeutic agent. Whole body scans were made at intervals for up to 15 days using the digital scanner, with the spectrometer set over the 364 keV photopeak of 131I. On the same occasions complete gamma-spectra were obtained for these patients using a 2 m arc, single detector whole body counter. The method used in estimating the activity at various sites in the body from the digital whole body scans is described and problems that arise in using 131I as a tracer for 32P Lipiodol in this work are discussed. For the administered activities mentioned above, maximum absorbed doses to the lymph nodes were found to range from 30-96 krad with a mean value of 51 krad. Uptake of radioactivity was also found in the lungs, resulting in absorbed doses of 350-960 rad with a mean value of 540 rad.