Laub W U, Kaulich T W, Nüsslin F
Department of Medical Physics, University of Tübingen, Germany.
Phys Med Biol. 1999 Sep;44(9):2183-92. doi: 10.1088/0031-9155/44/9/306.
A diamond detector type 60003 (PTW Freiburg) was examined for the purpose of dosimetry with 4-20 MeV electron beams and 4-25 MV photon beams. Results were compared with those obtained by using a Markus chamber for electron beams and an ionization chamber for photon beams. Dose distributions were measured in a water phantom with the detector connected to a Unidos electrometer (PTW Freiburg). After a pre-irradiation of about 5 Gy the diamond detector shows a stability in response which is better than that of an ionization chamber. The current of the diamond detector was measured under variation of photon beam dose rate between 0.1 and 7 Gy min(-1). Different FSDs were chosen. Furthermore the pulse repetition frequency and the depth of the detector were changed. The electron beam dose rate was varied between 0.23 and 4.6 Gy min(-1) by changing the pulse-repetition frequency. The response shows no energy dependence within the covered photon-beam energy range. Between 4 MeV and 18 MeV electron beam energy it shows only a small energy dependence of about 2%, as expected from theory. For smaller electron energies the response increases significantly and an influence of the contact material used for the diamond detector can be surmised. A slight sublinearity of the current and dose rate was found. Detector current and dose rate are related by the expression i alpha Ddelta, where i is the detector current, D is the dose rate and delta is a correction factor of approximately 0.963. Depth-dose curves of photon beams, measured with the diamond detector, show a slight overestimation compared with measurements with the ionization chamber. This overestimation is compensated for by the above correction term. The superior spatial resolution of the diamond detector leads to minor deviations between depth-dose curves of electron beams measured with a Markus chamber and a diamond detector.
为了对4 - 20 MeV电子束和4 - 25 MV光子束进行剂量测定，对型号为60003的金刚石探测器（PTW弗莱堡）进行了检测。将结果与使用马克斯电离室测量电子束以及使用电离室测量光子束所获得的结果进行了比较。在水模体中测量剂量分布，探测器连接到Unidos静电计（PTW弗莱堡）。在大约5 Gy的预辐照后，金刚石探测器的响应显示出比电离室更好的稳定性。在光子束剂量率在0.1至7 Gy min⁻¹之间变化的情况下测量了金刚石探测器的电流。选择了不同的源皮距（FSD）。此外，还改变了脉冲重复频率和探测器的深度。通过改变脉冲重复频率，电子束剂量率在0.23至4.6 Gy min⁻¹之间变化。在覆盖的光子束能量范围内，响应没有显示出能量依赖性。在4 MeV至18 MeV电子束能量之间，如理论预期，它仅显示出约2%的小能量依赖性。对于较小的电子能量，响应显著增加，可以推测金刚石探测器所用接触材料的影响。发现电流和剂量率存在轻微的次线性关系。探测器电流和剂量率由表达式i ∝ Dδ相关联，其中i是探测器电流，D是剂量率，δ是约为0.963的校正因子。用金刚石探测器测量的光子束深度剂量曲线与用电离室测量的结果相比显示出轻微的高估。这种高估通过上述校正项得到补偿。金刚石探测器优越的空间分辨率导致用马克斯电离室和金刚石探测器测量的电子束深度剂量曲线之间存在微小偏差。
