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首页> 外文期刊>Australasian physical & engineering sciences in medicine >Practical considerations for reporting surface dose in external beam radiotherapy: a 6 MV X-ray beam study
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Practical considerations for reporting surface dose in external beam radiotherapy: a 6 MV X-ray beam study

机译：报告外部束放射治疗中表面剂量的实际注意事项：6 MV X射线束研究

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摘要

In this study, we assessed the accuracy of surface doses determined by direct measurement and treatment planning system (TPS) calculations, relative to benchmark Monte Carlo (MC) doses calculated at 70 urn for a 6 MV, 10 × 10 cm clinical radiotherapy beam. In a homogeneous phantom with both open and fixed wedged fields, we found that the relative dose measured with an Attix chamber underestimates the MC calculated surface dose by 2.9 %, while the relative dose measured with EBT2 Gafchromic film overestimates the MC surface dose by 0.9 %. There was a significant over-response of up to 20 % in doses calculated at <2 mm depth with the Eclipse analytic anisotropic algorithm (AAA) compared to corresponding MC doses for an open field. This drops to <2 % at 2 mm depth. In a heterogeneous phantom, EBT2 film overestimates relative dose by up to 3.1 % compared to the MC calculated surface dose. The AAA relative dose calculated in a heterogeneous phantom at 2 mm depth agrees to within 1.5 % with the MC doses calculated at the same depth, but overestimates the MC surface dose (at 70 urn) by up to 2.5 %. Our results suggest that TPS doses evaluated near the surface be reported with a depth that should be at least 2 mm and this should be taken into consideration in the planned target volume for treatments where surface dose is a constraining factor. Our study demonstrates the usefulness of EBT2 film for measuring surface dose: under homogeneous conditions, the effective point of measurement of EBT2 film can be considered equivalent to the clinical skin depth of 70 urn.
机译：在这项研究中，我们评估了通过直接测量和治疗计划系统（TPS）计算确定的表面剂量的准确性，相对于对于6 MV，10×10 cm的临床放射治疗束在70 n下计算的基准蒙特卡洛（MC）剂量。在具有开放和固定楔形场的均质体模中，我们发现，使用Attix腔室测量的相对剂量低估了2.9％的MC计算表面剂量，而使用EBT2全色薄膜测量的相对剂量高估了0.9％的MC表面剂量。 。与空旷地区相应的MC剂量相比，使用Eclipse解析各向异性算法（AAA）在<2 mm深度处计算的剂量存在高达20％的显着过响应。在2 mm的深度处下降到<2％。与MC计算的表面剂量相比，在异质模型中，EBT2膜将相对剂量高估了高达3.1％。在2mm深度的异质体模中计算出的AAA相对剂量与在相同深度处计算出的MC剂量一致，在1.5％以内，但高估了MC表面剂量（70 um）高达2.5％。我们的结果表明，在表面附近评估的TPS剂量应报告至少2 mm的深度，并且在表面剂量是约束因素的治疗的计划目标体积中应考虑到这一点。我们的研究证明了EBT2膜用于测量表面剂量的有用性：在均匀条件下，EBT2膜的有效测量点可被认为等同于70微米的临床皮肤深度。

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