Metastases after fractionated radiation therapy of three murine tumor models

The incidence of lung metastases after fractionated radiation therapy was compared to single dose irradiation in a retrospective analysis of three murine tumor models. For FSaII and SCCVII 5 or 15 fractions over 5 days were given using curative and subcurative doses and photons and neutrons. Data were pooled from different experiments. In mice with locally controlled FSaII the incidence of lung metastases was the same after all treatments, whereas in mice with locally controlled SCCVII, metastases were enhanced after 15 fractions. Photon and neutron irradiations yielded similar results. Local recurrences were followed by increased metastases. MCaIV was subcuratively irradiated with 9 equal fractions followed by a top-up dose to achieve local control. Metastases were high if doses per fraction were low and interfraction time intervals long. The data on MCaIV indicate increased metastases if clonogenic cells during treatment represent a large proportion of the integral tumor burden. The results on FSaII and SCCVII indicate that fractionated treatments might differently influence distant metastasis in different tumor models.