title: Effect of dose fractionation on the enhancement by radiation or cyclophosphamide of artificial pulmonary metastases.
abstract: Thoracic irradiation or cyclophosphamide (CP) treatment of mice before an i.v. injection of tumour cells enhances the number of lung colonies produced by a factor of up to 100+. The effect of fractionation of the X-ray or CP dose on this phenomenon was investigated in several ways.The dose-response curve for the number of lung colonies as a function of the dose of thoracic irradiation was linear, and the degree of enhancement was independent of the number of tumour cells injected. Splitting a dose of 1,000 rad into 2 equal fractions separated by times varying from 1 to 24 h gave the same enhancement as that produced by a single dose of 1000 rad. Similarly, fractionation of 1000 rad into 5 × 200 rad, or 2000 rad into 5 × 400 rad (each interval between fractions being 3 h) had no effect on the radiation enhancement of colony formation.A single dose of 200 mg/kg of CP was compared with 3 doses of 66·7 mg/kg (each dose separated by 12 h) and with a continuous infusion of 200 mg/kg given over 24 h. In this case, fractionation and infusion produced a small reduction in the CP-induced increase, but the factor of colony enhancement compared to control mice remained >100.These data emphasize the potential hazard of prophylactic treatment of pulmonary metastases by X-rays or CP in clinical situations in which control of the primary tumour is not achieved.
mesh_terms: D000818:Animals; D003520:Cyclophosphamide / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D005260:Female; D008168:Lung / Q000187:drug effects* / Q000528:radiation effects*; D008175:Lung Neoplasms / Q000473:pathology*; D051379:Mice; D009362:Neoplasm Metastasis / Q000473:pathology*; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000473:pathology
chemical_list: D003520:Cyclophosphamide