[Assessment of tumor viability by 201Tl SPECT in VX-2 tumor-bearing rabbits after irradiation: comparison with X-ray CT and pathohistologic findings].

In order to evaluate 201Tl SPECT for the assessment of tumor viability after radiation therapy. Twenty rabbits were implanted with VX-2 tumor in the left femoral muscles and were classified into four groups as follows: normal control group (N), 20 Gy irradiated response group (A), 20 Gy irradiated non-response group (B), and 40 Gy irradiated group (C). Eight days after implantation, 201Tl SPECT and CT studies were performed to assess the changes in 201Tl uptake and tumor volume at 0, 1, 2, 3, and 4 weeks after single irradiation. Histologic specimens were also taken. In group N tumors continued to increase in volume, but 201Tl uptake showed a steady decrease after 2 weeks. In group A tumors continued to increase in volume, but 201Tl uptake showed a transient decrease at 2 weeks, then a steady increase. In group B tumors showed a transient increase in volume at 2 weeks, then a continuous decrease, but 201Tl uptake showed a continuous decrease throughout the study. In group C there was a continuous decrease both in volume and 201Tl uptake with the later more prominent. 201Tl uptake was decreased earlier than tumor volume both in group B and C, at one week that was significant (p < 0.01). 201Tl uptake by tumor reflects the burden of viable tumor on histology; therefore 201Tl SPECT is of great use in assessing the therapeutic effects on tumors.