High-activity radio-iodine labeling of conventional and stealth liposomes.

A new method to label preformed liposomes with high activities of radiohalogenated compounds has been developed. It uses activated esters of simple synthetic molecules that may be readily halogenated, such as Bolton-Hunter reagent (BH), and arginine-containing liposomes. BH, in the form of an activated ester, crosses the liposome membrane to react with arginine inside the liposomes, as demonstrated by thin-layer chromatography and by the fact that saline-containing liposomes, or hydrolyzed BH or the water soluble sulfo-BH afforded only marginal encapsulation yields. Under optimized conditions, between 37 and 55 degrees C, 62 +/- 4% (mean +/- SD) of radiolabeled BH were consistently encapsulated in the liposomes within 30 min. In molar amounts, this corresponds to a mean of 56 nmol of BH per micromol of lipids. Based on achievable specific activity, up to 2.8 GBq of iodine-131 could be entrapped per micromol of lipids. Leakage of radioactivity was very low, with less than 5% of the encapsulated activity released within 6 days at 4 degrees C in phosphate-buffered saline and less than 50% within 24 h in human serum at 37 degrees C. The labeling stability, and the fact that both conventional and PEGylated liposomes can be readily labeled with high doses of radioactivity, will make this technique useful for in vivo targeting applications, such as tumor detection (using iodine-123 or iodine-124) or therapy (with iodine-131 or astatine-211).

OEDIPE: a personalized dosimetric tool associating voxel-based models with MCNPX.

AIM: A new tool, named OEDIPE (a French acronym that stands for "Tool for Personalized Internal Dose Assessment") was developed to carry out personalized internal dosimetry calculations for nuclear medicine (for both therapeutic and diagnostic procedures) and for radiation safety (in the case of internal contamination). It was developed under the PV-Wave visual data analysis system by the Institute of Radioprotection and Nuclear Safety (IRSN) in collaboration with the French Institute of Health and Medical Research (INSERM). This software creates anthropomorphic voxel-based phantoms from computed tomography (CT) and magnetic resonance imaging (MRI) patient images through the use of a friendly graphical user interface (GUI). Several tools have been built-in to allow for image segmentation. Source data, including VOI localization and cumulated activities, are assessed by single photon emission computed tomography (SPECT) images, and the source may be specified in any number of organs either as a point source or a homogeneously distributed source. It is also possible to choose the dosimetric parameters required for the study (mean organ dose or a dose distribution). Phantom, source, and dosimetric parameters are automatically written into a file. That file is then processed by the Monte Carlo code MCNPX (LANL) to perform the actual dose calculation. RESULTS: OEDIPE can compute either the absorbed dose in each organ (in a few minutes), or the absorbed dose in each voxel of the phantom (i.e. the spatial dose distribution at a tissue level) in a few hours or more. OEDIPE automatically reads the MCNPX output file and processes results to give a list of absorbed doses in each organ or a plot of isodose curves superimposed onto the phantom. Because of the long calculation times required to compute an absorbed dose within an entire whole-body phantom at a spatial resolution of a few millimeters, modifications were made to reduce computational times to reasonable values. To illustrate this tool, results of a dosimetric study of technetium-99m labeling of a bone-scanning agent are presented. CONCLUSION: OEDIPE is a tool that can be used for patient-specific dosimetry--for example, in targeted radiotherapy--by taking into account the individual patient anatomy, including tumors.