Effect of a change in reactor power on response of murine solid tumors <i>in vivo</i>, referring to impact on quiescent tumor cell population.

<b>Purpose:</b> To examine the effect of a change in reactor power on the response of solid tumors, referring to impact on quiescent (Q) tumor cell population. <b>Materials and Methods:</b> Tumor-bearing mice received 5-bromo-2-deoxyuridine (BrdU) to label all proliferating (P) tumor cells, and were treated with boronophenylalanine-¹⁰B (BPA) or sodium mercaptododecaborate-¹⁰B (BSH). After reactor neutron beam irradiation at a power of 1 or 5 MW with an identical beam spectrum, cells from tumors were isolated and incubated with a cytokinesis blocker. The responses of BrdU-unlabeled Q and total (= P + Q) tumor cells were assessed based on the frequencies of micronucleation using immunofluorescence staining for BrdU. <b>Results:</b> After neutron irradiation with or without <b>¹⁰</b>B-carrier, radio-sensitivity was reduced by decreasing reactor power in both cells, especially in Q cells and after irradiation with BPA. The values of relative and compound biological effectiveness were larger at a power of 5 MW and in Q cells than at a power of 1 MW and in total cells, respectively. The sensitivity difference between total and Q cells was widened when combined with <b>¹⁰</b>B-carrier, especially with BPA, and through decreasing reactor power. <b>Conclusion:</b> 5 MW is more advantageous than 1 MW for boron neutron capture therapy.