Kry Stephen F, Price Michael, Followill David, Mourtada Firas, Salehpour Mohammad
Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, U.S.A.
J Appl Clin Med Phys. 2007 Sep 24;8(4):169-175. doi: 10.1120/jacmp.v8i4.2679.
The commonly used thermoluminescent dosimeter TLD-100 (Harshaw Chemical Company, Solon, OH) responds not only to photons and electrons, but also to neutrons that are produced during high-energy therapies. As a result, TLD-100 measurements outside of the treatment field are suspect when high-energy radiation is used. Although alternatives such as TLD-700 do not respond to neutrons, specialty dosimeters of this kind are expensive and are not routinely used in most clinics. In the current study, we examined the accuracy of TLD-100 in measuring the out-of-field photon dose as a function of treatment energy. To determine the accuracy of TLD-100 as compared with TLD-700, TLD-100 was irradiated outside of the treatment field by medical accelerators operated at 6, 10, 15, and 18 MV. In an effort to eliminate the response of TLD-100 to neutrons, TLD capsules were encased in varying thicknesses of cadmium foil (0.25 - 0.75 mm) before being irradiated at 18 MV. The out-of-field TLD-100 was found to be accurate at 6 MV and 10 MV, but to be substantially over-responsive at 15 MV and 18 MV (by up to 1063% relative to TLD-700). By wrapping the TLD-100 in up to 0.75 mm of cadmium, it was possible to drastically reduce (down to 39% on average) the over-response of the TLD-100; however, total removal of the over-responsiveness was not possible. Although TLD-100 is well suited for measuring out-of-field dose at energies as high as 10 MV, at higher energies (15 MV or greater), this dosimeter over-responds substantially and should not be used. Although encasing the TLD in cadmium minimized over-response to a degree, the reduction was not sufficient to make TLD-100 viable for measuring out-of-field dose at high treatment energies.
常用的热释光剂量仪TLD - 100（哈肖化学公司，俄亥俄州索伦）不仅对光子和电子有响应，而且对高能治疗过程中产生的中子也有响应。因此，当使用高能辐射时，治疗野之外的TLD - 100测量结果值得怀疑。虽然诸如TLD - 700之类的替代品对中子没有响应，但这类专用剂量仪价格昂贵，在大多数诊所并非常规使用。在本研究中，我们研究了TLD - 100在测量野外光子剂量方面的准确性与治疗能量的函数关系。为了确定TLD - 100与TLD - 700相比的准确性，TLD - 100在治疗野外由运行于6、10、15和18兆伏的医用加速器进行照射。为了消除TLD - 100对中子的响应，TLD胶囊在18兆伏照射前用不同厚度（0.25 - 0.75毫米）的镉箔包裹。发现野外TLD - 100在6兆伏和10兆伏时是准确的，但在15兆伏和18兆伏时响应过度（相对于TLD - 700高达1063%）。通过将TLD - 100包裹在厚度达0.75毫米的镉中，有可能大幅降低（平均降至39%）TLD - 100的过度响应；然而，不可能完全消除过度响应。尽管TLD - 100非常适合测量高达10兆伏能量的野外剂量，但在更高能量（15兆伏或更高）时，这种剂量仪响应过度明显，不应使用。虽然将TLD包裹在镉中在一定程度上使过度响应最小化，但减少程度不足以使TLD - 100在高治疗能量下测量野外剂量时可行。
