The effect of radiation therapy on fungal growth: results of in vitro and in vivo studies

Objectives. To investigate the effect of radiation therapy (XRT) on the growth of Candida and Cryptococcus. Methods. (1) In vitro study: suspensions of Candida and Cryptococcus were irradiated by 0-20 Gy, and colony forming units (CFUs) were counted after 2 and 11 days. (II) In vivo study: (A) The XRT effect-Balb/c mice were injected with Candida or Cryptococcus and irradiated by 5 or 10 Gy. Homogenates of their kidneys or brains were cultured and CFUs were counted two days later. (B) Toxicity-Balb/c mice were injected with Candida and irradiated by 5 Gy. Control mice were either injected or irradiated. Overall survival was documented for all. animals. Results. (I) The CFU counts in the irradiated and non-irradiated mice were similar at days 2 and 11. (II) (A)-The CFUs were significantly low for both Candida and Cryptococcus injected and irradiated mice (p = 0.02). (II) (B)-The overall survival of the injected mice was not affected by the additional irradiation and it was inferior to the irradiated mice only. Conclusions. XRT has a beneficial inhibitive effect on the in vivo but not the in vitro growth of fungi. It does not decrease the survival rate of injected mice. Clinical studies in selected patients with resistant invasive fungal infection are warranted. (c) 2004 The British Infection Society. Published by Elsevier Ltd. All rights reserved.