Department of Radiation Oncology, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Hiroshima 734-8551, Japan.
Department of Radiation Oncology, Niigata University Medical and Dental Hospital, Niigata, Niigata, 951-8122, Japan.
Br J Radiol. 2020 Jul;93(1111):20200125. doi: 10.1259/bjr.20200125. Epub 2020 May 7.
To evaluate the biological effectiveness of dose associated with interruption time; and propose the dose compensation method based on biological effectiveness when an interruption occurs during photon radiation therapy.
The lineal energy distribution for human salivary gland tumor was calculated by Monte Carlo simulation using a photon beam. The biological dose (D) was estimated using the microdosimetric kinetic model. The dose compensating factor with the physical dose for the difference of the D with and without interruption (Δ) was derived. The interruption time (τ) was varied to 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 10, 20, 30, 40, 50, 75, and 120 min. The dose per fraction and dose rate varied from 2 to 8 Gy and 0.1 to 24 Gy/min, respectively.
The maximum Δ with 1 Gy/min occurred when the interruption occurred at half the dose. The Δ with 1 Gy/min at half of the dose was over 3% for τ >= 20 min for 2 Gy, τ = 10 min for 5 Gy, and τ = 10 min for 8 Gy. The maximum difference of the Δ due to the dose rate was within 3% for 2 and 5 Gy, and achieving values of 4.0% for 8 Gy. The dose compensating factor was larger with a high dose per fraction and high-dose rate beams.
A loss of biological effectiveness occurs due to interruption. Our proposal method could correct for the unexpected decrease of the biological effectiveness caused by interruption time.
For photon radiotherapy, the interruption causes the sublethal damage repair. The current study proposed the dose compensation method for the decrease of the biological effect by the interruption.
评估与中断时间相关的剂量的生物学效应，并在光子放射治疗过程中发生中断时，提出基于生物学效应的剂量补偿方法。
使用蒙特卡罗模拟方法对人唾液腺癌的线性能量分布进行计算，采用微剂量动力学模型估算生物剂量（D）。推导了在有和没有中断的情况下，D 的差异（Δ）与物理剂量的剂量补偿因子。中断时间（τ）分别变化为 0.1、0.2、0.3、0.4、0.5、1、2、3、4、5、10、20、30、40、50、75 和 120 分钟。每个分数的剂量和剂量率分别从 2 到 8 Gy 和 0.1 到 24 Gy/min 变化。
当中断发生在剂量的一半时，出现了 1 Gy/min 的最大Δ。当 τ >= 20 min 时，2 Gy 的中断时间为 10 min，5 Gy 的中断时间为 10 min，8 Gy 的中断时间为 10 min，1 Gy/min 的Δ超过 3%。由于剂量率引起的Δ的最大差异在 2 和 5 Gy 内为 3%以内，而 8 Gy 时达到 4.0%。高剂量分数和高剂量率的射线束的剂量补偿因子较大。
中断会导致生物学效应的损失。我们提出的方法可以纠正由于中断时间引起的生物学效应的意外下降。
对于光子放射治疗，中断会导致亚致死损伤修复。本研究提出了一种用于补偿中断导致生物学效应下降的剂量补偿方法。
