Pneumocystis Jiroveci Infection and Craniospinal Irradiation with Arc Therapy: a Report of Two cases

Abstract

Tomotherapy, a form of arc therapy, is often preferred to craniospinal irradiation (CSI) because of its better dose homogeneity when planning target volume and minimising organ risk. We report the cases of two young men with central nervous system germ cell tumour who had unnoticed severe and prolonged lymphopenia after completing CSI with tomotherapy. Both developed Pneumocystis jiroveci pneumonia and one died of respiratory failure. We hypothesise that the rapid drop in lymphocyte count may have been in part due to the ‘low dose bath’ of radiation to the whole pulmonary vasculature with consequent killing of the circulating lymphocytes, in addition to low-dose radiation to a high volume of the thymus, thoracic duct, and bone marrow. We therefore suggest close monitoring of lymphocyte count during tomotherapy-CSI and consideration of co-trimoxazole prophylaxis in severe lymphopenic patients. Further large-scale study is required to understand the possible correlation of V1-V5 lung dosimetry with risk of lymphopenia.