[Effects of split dose irradiation on monolayer cells and multicellular tumor spheroid]

Human neuroblastoma (GOTO) and squamous cell carcinoma (SQ5), grown as the monolayer cells or as the multicellular tumor spheroid (MTS) were irradiated. GOTO cells were radiosensitive, while SQ5 cells were moderately radioresistant. Cells were irradiated by the single or the split doses and the recovery between split doses were investigated. The recovery ratio (R.R.) of monolayer cells were calculated by the procedure A: the dose ratio at the same survival levels or by the procedure B: the survival rates ratio at the same doses. The therapeutic response of MTS was determined by the method of spheroid control dose-50 (SCD50) and R.R. of MTS was calculated by the ratio of the values of SCD50. R.R. of GOTO-monolayer cells was 1.1 (by the procedure A) and 1.6 (by the procedure B). GOTO-MTS did not show the significant difference between SCD50 of single dose irradiation and that of split doses one. When SQ5 cells were irradiated by the split doses, R.R.s obtained by the procedure A and B were 1.3 and 2.1, respectively. R.R. of SQ5-MTS was not different from that of monolayer cells obtained by the procedure A. MTS with two different sizes were irradiated by the single or split doses, and there was no remarkable difference with respect to the radiocurability and R.R. Although the number of cell lines were limited, their growth condition did not affect the capacity of recovery from radiation damage.