Kliauga P, Amols H
Columbia University College of Physicians and Surgeons, Center for Radiological Research, New York, NY 10032.
Int J Radiat Oncol Biol Phys. 1995 Feb 1;31(3):629-33. doi: 10.1016/0360-3016(94)00370-Z.
A new method of measuring photoneutron dose to the patient during treatment with high energy photon or electron beams is presented. This method has the advantage of providing not only the dose, but the microdosimetric spectrum at the same time.
A miniature cylindrical gas proportional counter (0.5 mm diameter by 0.5 mm height) has been used to measure scatter radiation from a 20 MV teletherapy photon beam. At atmospheric pressure, filled with propane base tissue equivalent gas, this counter simulates a unit density tissue region of approximately 0.9 microns. We present here single event microdosimetric spectra measured outside the primary beam 1.4 m from the target. This technique allows a single measurement to determine the scattered dose due to gammas and photoneutron contamination, as well as the quality factor of the photoneutrons.
Spectral components from scattered photons and the photoneutrons are easily separated, and dose contributions can be estimated. The ratio of photoneutron dose measured by the proportional counter to photon dose at isocenter is 0.75 x 10(-4).
Neutron dose was also measured using a bubble neutrometer. The proportional counter and neutrometer agree within experimental errors. This type of instrument is shown to be a viable technique for determination of exposure of patient and also personnel to photoneutrons, providing not only a dose determination, but also a spectrum that can be used to estimate quality factors for equivalent dose. Its main drawback is that it requires a lengthy (several hours) measurement because of low count rate of the neutrons.
提出一种在高能光子或电子束治疗期间测量患者光中子剂量的新方法。该方法的优点是不仅能提供剂量，还能同时提供微剂量谱。
使用一个微型圆柱形气体正比计数器（直径0.5毫米，高0.5毫米）来测量20兆伏远距离治疗光子束的散射辐射。在大气压下，填充丙烷基组织等效气体，该计数器模拟一个约0.9微米的单位密度组织区域。我们在此展示了在距靶1.4米处的原射线束外测量的单事件微剂量谱。该技术允许单次测量来确定由于γ射线和光中子污染导致的散射剂量，以及光中子的品质因数。
散射光子和光中子的谱成分很容易分离，并且可以估计剂量贡献。正比计数器测量的光中子剂量与等中心处光子剂量的比值为0.75×10⁻⁴。
还使用气泡中子测量仪测量了中子剂量。正比计数器和中子测量仪在实验误差范围内一致。这种类型的仪器被证明是一种可行的技术，可用于确定患者以及工作人员对光中子的照射，不仅能进行剂量测定，还能提供一个可用于估计当量剂量品质因数的谱。其主要缺点是由于中子计数率低，需要进行长时间（数小时）的测量。
