Wuu C S, Kliauga P, Zaider M, Amols H I
Department of Radiation Oncology, Columbia University, New York, NY 10032, USA.
Int J Radiat Oncol Biol Phys. 1996 Oct 1;36(3):689-97. doi: 10.1016/s0360-3016(96)00374-4.
To determine the microdosimetric-derived relative biological effectiveness (RBE) of 103Pd, 125I, 241Am, and 192Ir brachytherapy sources at low doses and/or low dose rates.
The Theory of Dual Radiation Action can be used to predict expected RBE values based on the spatial distribution of energy deposition at microscopic levels from these sources. Single-event lineal energy spectra for these isotopes have been obtained both experimentally and theoretically. A grid-defined wall-less proportional counter was used to measure the lineal energy distributions. Unlike conventional Rossi proportional counters, the counter used in these measurements has a conducting nylon fiber as the central collecting anode and has no metal parts. Thus, the Z-dependence of the photoelectric effect is eliminated as a source of measurement error. Single-event spectra for these brachytherapy sources have been also calculated by: (a) the Monte Carlo code MCNP to generate the electron slowing down spectrum, (b) transport of monoenergetic electron tracks, event by event, with our Monte Carlo code DELTA, (c) using the concept of associated volume to obtain the lineal energy distribution f(y) for each monoenergetic electron, and (d) obtaining the composite lineal energy spectrum for a given brachytherapy source based on the electron spectrum calculated at step (a).
Relative to 60Co, the RBE values obtained from this study are: 2.3 for 103Pd, 2.1 for 125I, 2.1 for 241Am, and 1.3 for 192Ir.
These values are consistent with available data from in vitro cell survival experiments. We suggest that, at least for these brachytherapy sources, microdosimetry may be used as a credible alternative to time-consuming (and often uncertain) radiobiological experiments to obtain information on radiation quality and make reliable predictions of RBE in low dose rate brachytherapy.
确定¹⁰³Pd、¹²⁵I、²⁴¹Am和¹⁹²Ir近距离治疗源在低剂量和/或低剂量率下由微剂量学得出的相对生物效应（RBE）。
双辐射作用理论可用于根据这些源在微观水平上的能量沉积空间分布来预测预期的RBE值。这些同位素的单事件线能量谱已通过实验和理论方法获得。使用网格定义的无壁正比计数器来测量线能量分布。与传统的罗西正比计数器不同，这些测量中使用的计数器以导电尼龙纤维作为中央收集阳极，且没有金属部件。因此，消除了光电效应的Z依赖性作为测量误差源。这些近距离治疗源的单事件谱也通过以下方式计算：(a) 使用蒙特卡罗代码MCNP生成电子慢化谱；(b) 使用我们的蒙特卡罗代码DELTA逐个事件地传输单能电子轨迹；(c) 使用关联体积的概念获得每个单能电子的线能量分布f(y)；(d) 根据步骤(a)计算的电子谱获得给定近距离治疗源的复合线能量谱。
相对于⁶⁰Co，本研究获得的RBE值为：¹⁰³Pd为2.3，¹²⁵I为2.1，²⁴¹Am为2.1，¹⁹²Ir为1.3。
这些值与体外细胞存活实验的现有数据一致。我们建议，至少对于这些近距离治疗源，微剂量学可作为耗时（且往往不确定）的放射生物学实验的可靠替代方法，以获取有关辐射质量的信息，并在低剂量率近距离治疗中对RBE做出可靠预测。
