Hematological Toxicity Induced by Bone Metastasis Radiation Therapy

Radiotherapy is frequently used in patients with bone metastasis. However, radiotherapy for bone metastasis may cause clinically significant hematological toxicity both by depleting the blood cells and by damaging the proliferating bone marrow. In general, lymphocytes (T cells, B cells and natural killer cells) are among the most radiosensitive cells, followed by monocytes and macrophages. As the most radiosensitive cells in the hematopoietic system, radiotherapy induced lymphopenia occurs immediately after irradiation and shows a nadir within 1–2 months after the initiation of radiotherapy. Radio-induced hematotoxicity is a significant clinical problem affecting treatment outcome and survival of cancer patients. This toxicity results from the direct effects of radiation on circulating lymphocytes and the indirect effects on stem cells in the bone marrow.