Lymphocyte-sparing radiotherapy

2018 Fiscal Year Final Research Report

• Project/Area Number: 17K16458
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Radiation science
• Research Institution: Kumamoto University
• Principal Investigator: Saito Tetsuo 熊本大学, 医学部附属病院, 講師 (30467980)
• Project Period (FY): 2017-04-01 – 2019-03-31
• Keywords: リンパ球減少 / 放射線治療

Outline of Final Research Achievements

We retrospectively assessed patients who had received palliative radiotherapy. The absolute volume of bone marrow that had received 5, 10, 20, and 30 Gy was recorded. Overall, hematologic toxicity (white blood cell, absolute neutrophil count, and platelet) was relatively mild. No bone marrow dose-volume parameter was a significant predictor of hematologic toxicity of grade 2 or higher. Many patients experienced lymphopenia of grade 3 or higher. These findings indicate the high sensitivity of lymphocyte to irradiation.
Patients with esophageal cancer who had received definitive chemoradiotherapy at our Institution were retrospectively assessed. Spleen dose-volume parameters (V5, V10, V20, V30, and mean splenic dose) were significant independent factors negatively influencing the absolute lymphocyte count at nadir. Higher spleen dose-volume parameters were associated with severe lymphopenia during radiotherapy.

Free Research Field

放射線腫瘍学

Academic Significance and Societal Importance of the Research Achievements

腫瘍免疫において重要な役割を担うT・Bリンパ球に対して、放射線治療は相反する二つの作用を持つ。リンパ球の腫瘍への攻撃に促進的に作用する一方、リンパ球数を減少させることで抑制的にも作用する。本研究では、放射線治療によるリンパ球数減少を軽減することにより、放射線治療の腫瘍免疫への促進的な効果を十分に享受する治療法の確立を目指す。過去の我々の研究結果と合わせ、放射線治療後にリンパ球減少のリスクの高いのは、①照射される体の容積が大きく、②照射回数が多く、③脾臓の多くに高線量照射される場合と考えられる。リンパ球を温存する放射線治療を開発する上ではこれらの要素を考慮に入れる必要がある。