Anton Mathias
Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany.
Phys Med Biol. 2006 Nov 7;51(21):5419-40. doi: 10.1088/0031-9155/51/21/003. Epub 2006 Oct 6.
In radiation therapy, the effect of ionizing radiation is quantified in terms of the absorbed dose to water. Dosimetry with alanine and readout via electron spin resonance (ESR) is a method which is used as a secondary standard by several national metrology institutions. The advantages of the method are the good water-equivalence of the probes, their small size and the very weak dependence of the response on the radiation quality for MV x-rays and high-energy electrons used in radiation therapy. For radiation therapy, a small uncertainty of the applied dose is required. The present publication describes the determination of the uncertainty budget for the alanine/ESR dosimetry system of the Physikalisch-Technische Bundesanstalt (PTB), which relies on the use of a reference sample. A method is also presented which allows a reduction of the influence of fading or other changes of the ESR amplitude of irradiated alanine probes with time. If certain conditions are met which are described in detail, a relative uncertainty of less than 0.5% can be reached for probes irradiated with (60)Co in the 5-25 Gy dose range, including the uncertainty of the primary standard. First results for dose values between 2 Gy and 10 Gy are presented as well. From the high accuracy achievable with alanine dosimetry, we conclude that this method has great potential to solve measurement problems for modern methods of radiation therapy such as intensity modulated radiation therapy (IMRT) or tomotherapy.
在放射治疗中，电离辐射的效应通过水的吸收剂量来量化。使用丙氨酸进行剂量测定并通过电子自旋共振（ESR）进行读数，是一种被多个国家计量机构用作二级标准的方法。该方法的优点是探测器具有良好的水等效性、尺寸小，并且对于放射治疗中使用的兆伏级X射线和高能电子，其响应对辐射质量的依赖性非常弱。对于放射治疗，要求所施加剂量的不确定性很小。本出版物描述了德国物理技术研究院（PTB）丙氨酸/ESR剂量测定系统不确定度预算的确定方法，该方法依赖于参考样品的使用。还提出了一种方法，该方法可以减少辐照丙氨酸探测器的ESR幅度随时间的衰减或其他变化的影响。如果满足详细描述的某些条件，对于在5 - 25 Gy剂量范围内用（60）Co辐照的探测器，包括一级标准的不确定度，相对不确定度可以达到小于0.5%。还给出了2 Gy至10 Gy剂量值的初步结果。从丙氨酸剂量测定可实现的高精度，我们得出结论，该方法在解决现代放射治疗方法（如调强放射治疗（IMRT）或断层放射治疗）的测量问题方面具有巨大潜力。
