Ten Haken R K, Fraass B A, Jost R J
Department of Radiation Oncology, University of Michigan Medical School, Ann Arbor 48109.
Med Phys. 1987 Nov-Dec;14(6):1060-6. doi: 10.1118/1.595986.
Central axis relative dose versus depth measurements were performed using two different small volume thimble ionization chambers and a p-type silicon diode in a water phantom and with two parallel-plate ionization chambers, thermoluminescent dosimeters, and radiographic film in a popular clear polystyrene phantom. Values obtained were compared to the results of similar measurements in a water phantom performed with a plane-parallel ionization chamber designed and optimized for use in electron beams by the Nordic Association of Clinical Physicists (NACP). The NACP chamber is expected to minimally perturb the electron fluence and be least prone to point of measurement uncertainties. Its use in a water phantom closely approximates the spirit of recent international protocols. Data were obtained for the foil scattered electron beams generated by two different accelerators for field sizes from 6 cm X 6 cm to 25 cm X 25 cm and energies between 6 and 20 MeV. Easily identifiable effective points of measurements were defined for each measurement device and standard corrections were applied to the raw data to obtain depth-dose curves. The degree of agreement between the various techniques and the NACP-water standard was quantitatively analyzed through comparison of the resulting depths of 50% dose and practical range. All methods were found to yield reasonable results when carefully implemented, with average differences of less than 1 mm being easily achievable. Measurements with p-type silicon diode detectors were found to be particularly useful, as they are pointlike and appear from all practical considerations to directly represent relative dose, thus requiring little or no correction to raw readings.
使用两个不同的小体积指形电离室和一个p型硅二极管在水模体中进行中心轴相对剂量与深度的测量，并使用两个平行板电离室、热释光剂量计和射线照相胶片在一种常用的透明聚苯乙烯模体中进行测量。将获得的值与在水模体中使用由北欧临床物理学家协会（NACP）设计和优化用于电子束的平行板电离室进行的类似测量结果进行比较。预计NACP电离室对电子注量的扰动最小，且最不容易出现测量点的不确定性。在水模体中使用它与最近国际协议的精神非常接近。获得了由两台不同加速器产生的箔散射电子束在6 cm×6 cm至25 cm×25 cm的射野尺寸和6至20 MeV能量下的数据。为每个测量设备定义了易于识别的有效测量点，并对原始数据应用标准校正以获得深度剂量曲线。通过比较所得的50%剂量深度和实际射程，定量分析了各种技术与NACP水标准之间的一致性程度。发现所有方法在仔细实施时都能产生合理的结果，平均差异很容易达到小于1 mm。发现使用p型硅二极管探测器进行测量特别有用，因为它们是点状的，从所有实际考虑来看似乎直接代表相对剂量，因此对原始读数几乎不需要或不需要校正。
