TUMOR REPOPULATION DURING RADIOTHERAPY - QUANTITATION IN 2 XENOGRAFTED HUMAN TUMORS

Purpose: ''Accelerated repopulation'' has generated considerable recen t interest, Our purpose in this study was to determine whether flow cy tometry measurements like those used for classical T-pot determination s could be used to quantify the rate of repopulation, and the time of its initiation in irradiated human tumor xenografts. Methods and Mater ials: Two human tumor cell lines (SiHa, a squamous cell cervix carcino ma, and WiDr, an adenocarcinoma of the colon) were grown as Subcutaneo us xenografts in SCID mice. T-pot was measured in a conventional manne r using how cytometry, for control tumors and for tumors exposed to fi ve fractions of 4 Gy twice daily over a 2-day interval, For the irradi ated tumors, T-pot measurements were conducted 48 h following the fina l exposure. Results: Active proliferation even after irradiation was o bserved in both the radiosensitive SiHa and more radioresistant WiDr t umors, and the estimated repopulation rate was at least as fast as wou ld have been predicted by the pre-treatment T-pot estimates. Conclusio ns: Our data clearly indicate tumor cell proliferation after only a fe w fractions of radiation exposure in these human tumor xenografts, Add itionally, the data suggest that pretreatment T-pot values may underes timate the actual regrowth rate. (C) 1997 Elsevier Science Inc.