Pneumocystis jiroveci Infection and Craniospinal Irradiation with Arc Therapy: a Report of Two Cases
TH So, PYP Ho, TW Leung, DLW Kwong
Hong Kong J Radiol 2016;19:126-31
DOI: 10.12809/hkjr1615329
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.
中文摘要
肺囊蟲感染及採用圓弧式照射的脊髓放療：兩例病例報告
蘇子謙、何沛盈、梁道偉、鄺麗雲
螺旋斷層放療是一種弧形放射治療，由於在規劃靶體積時能達至放射劑量均一性，所以能減少對於其他器官的風險，因而比顱脊髓放療（CSI）較佳。本文報告兩名中樞神經系統生殖細胞腫瘤的年輕患者在接受螺旋斷層CSI後出現了嚴重和持久的淋巴細胞減少症，並未被重視。兩人均有肺囊蟲肺炎，其中一人因呼吸衰竭導致死亡。我們認為導致淋巴細胞數量迅速下降的原因是除了以低劑量輻射照射大範圍的胸腺、胸導管和骨髓外，亦因使用低劑量輻射照射全肺血管而殺死循環淋巴細胞。我們建議使用螺旋斷層CSI時要密切監測病人的淋巴細胞數量，並對於淋巴細胞減少症患者考慮處方預防性藥物co-trimoxazole。須進一步進行大規模的研究以探討V1-V5肺劑量與淋巴細胞減少症可能存在的關係。