SELECTED PRESENTATIONS  THERAPY AND DOSIMETRY IN NUCLEAR MEDICINE - AN UPDATE 

The Quarterly Journal of Nuclear Medicine and Molecular Imaging 2012 December;56(6):487-95

Copyright © 2013 EDIZIONI MINERVA MEDICA

lingua: Inglese

Quantification of activity by alpha-camera imaging and small-scale dosimetry within ovarian carcinoma micrometastases treated with targeted alpha therapy

Chouin N. ^{1, 2}, Lindegren S. ², Jensen H. ³, Albertsson P. ⁴, Bäck T. ² ✉

¹ LUNAM Université, Oniris, « AMaROC », Nantes, F-44307, France; ² Department of Radiation Physics, Institute of Clinical, Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden; ³ Cyclotron and PET Unit, KF-3982, Rigshospitalet, Copenhagen, Denmark; ⁴ Department of Oncology, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden

Targeted alpha therapy (TAT) a promising treatment for small, residual, and micrometastatic diseases has questionable efficacy against malignant lesions larger than the α-particle range, and likely requires favorable intratumoral activity distribution. Here, we characterized and quantified the activity distribution of an alpha-particle emitter radiolabelled antibody within >100-µm micrometastases in a murine ovarian carcinoma model. Nude mice bearing ovarian micrometastases were injected intra-peritoneally with 211At-MX35 (total injected activity 6 MBq, specific activity 650 MBq/mg). Animals were sacrificed at several time points, and peritoneal samples were excised and prepared for alpha-camera imaging. Spatial and temporal activity distributions within micrometastases were derived and used for small-scale dosimetry. We observed two activity distribution patterns: uniform distribution and high stable uptake (>100% IA/g at all time points) in micrometastases with no visible stromal compartment, and radial distribution (high activity on the edge and poor uptake in the core) in tumor cell lobules surrounded by fibroblasts. Activity distributions over time were characterized by a peak (140% IA/g at 4 h) in the outer tumor layer and a sharp drop beyond a depth of 50 µm. Small-scale dosimetry was performed on a multi-cellular micrometastasis model, using time-integrated activities derived from the experimental data. With injected activity of 400 kBq, tumors exhibiting uniform activity distribution received <25 Gy (EUD=13 Gy), whereas tumors presenting radial activity distribution received mean absorbed doses of <8 Gy (EUD=5 Gy). These results provide new insight into important aspects of TAT, and may explain why micrometastases >100 µm might not be effectively treated by the examined regimen.