Radiolabeled thymidine: a sensitive tracer for early tumor response and recurrence after irradiation.
This study evaluated the sensitivity of a radiolabeled thymidine tracer for assessment of early tumor response and recurrence after irradiation.


METHODS
SW707 human colon carcinoma implanted into nude mice was irradiated with 6 or 20 Gy. Tumor volume was determined for an interval of 14 d. At 4, 8 and 24 h and at 2, 3, 7, 10 and 14 d after irradiation, [14C]thymidine uptake into the tumor was determined with a liquid scintillation counter and the intratumoral distribution of [14C]thymidine was visualized and evaluated semiquantitatively by autoradiography using a phosphor imager.


RESULTS
In both groups, tumor volume decreased until day 7 after irradiation; afterward, regrowth occurred in only the group that had received 6 Gy. A decrease in thymidine uptake was found as early as 8 h after irradiation. On day 3 after irradiation, thymidine uptake increased again in the 6-Gy group, before the increase in tumor volume, but remained unchanged in the 20-Gy group. Also on day 3, multiple foci of thymidine uptake suggesting proliferation preceding tumor recurrence were seen on autoradiographs from the 6-Gy group but not from the 20-Gy group. Histological findings correlated with the results of autoradiography.


CONCLUSIONS
The results show that radiolabeled thymidine is a sensitive tracer for assessment of early tumor response and recurrence after irradiation. The rapid decrease in uptake, however, does not allow any prediction about tumor recurrence.
Senekowitsch-Schmidtke
R
R
Department of Nuclear Medicine, Technische Universität München, Germany.
Rüth
F
F
Bernatz
S
S
D000818:Animals; D001345:Autoradiography; D002250:Carbon Radioisotopes; D003110:Colonic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009364:Neoplasm Recurrence, Local / Q000000981:diagnostic imaging* / Q000473:pathology; D009368:Neoplasm Transplantation; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D011879:Radiotherapy Dosage; D012588:Scintillation Counting; D013936:Thymidine; D013997:Time Factors
D002250:Carbon Radioisotopes; D019275:Radiopharmaceuticals; D013936:Thymidine