Department of Radiotherapy, ICANS, Institut Cancérologie Strasbourg Europe, 67200 Strasbourg Cedex, France; Strasbourg University, CNRS, IPHC UMR 7178, Centre Paul Strauss, UNICANCER, 67000 Strasbourg, France.
Department of Orthopedic Surgery and Traumatology, Hautepierre University Hospital, 67098 Strasbourg Cedex, France.
Chin Clin Oncol. 2020 Apr;9(2):14. doi: 10.21037/cco.2020.01.09. Epub 2020 Feb 11.
Metallic implants (MIs) complicate radiotherapy planning. Several studies have worked on tissue-equivalent phantoms as experimental models to estimate dose distributions in this context. The application of these results to clinical practice remains disputable because the inhomogeneity of human tissue densities is a difficult factor to integrate into dose calculation software. In this work, we evaluate the impact of human tissue inhomogeneities by assessing the discrepancies between treatment planning system (TPS) dose calculations and measured delivered doses on a human cadaver with hip prostheses.
A total of 143 alanine dosimeters were positioned in contact with the prostheses (bones group), soft tissues (soft tissues group), skin surfaces (skin group) and natural cavities (cavities group) of a human cadaver. The planning target volume (PTV) corresponded to a standard endometrial cancer treatment. The irradiation was performed with 6 MV X-ray tomotherapy at the one fraction-dose of 10 Gy.
A total of 140 dosimeters were analyzed. After applying a temperature correction coefficient to the measured doses, the global analysis of all dosimeters showed a significant difference between the calculated doses and the measured doses (P<0.001). For dosimeters of the bones, soft tissues, skin and cavities groups, this difference was also significant (P<0.001 for each group). The mean measured doses were 21.9% lower than the mean calculated doses in the global analysis and 17.0%, 21.2%, 33.0% and 19.0% lower for the bones, soft tissues, skin and cavities groups, respectively.
This study showed that the received doses were significantly lower than the calculated doses and suggested the need to improve the understanding of this discrepancy.
金属植入物（MIs）会使放疗计划变得复杂。有几项研究致力于使用组织等效体模作为实验模型，以估算这种情况下的剂量分布。然而，将这些结果应用于临床实践仍然存在争议，因为人体组织密度的不均匀性是难以纳入剂量计算软件的一个因素。在这项工作中，我们通过评估带有髋关节假体的人体尸体上治疗计划系统（TPS）剂量计算与测量的剂量之间的差异来评估人体组织不均匀性的影响。
总共在假体（骨骼组）、软组织（软组织组）、皮肤表面（皮肤组）和自然腔（腔组）与人体尸体接触的位置放置了 143 个 alanine 剂量计。规划靶区（PTV）对应于标准的子宫内膜癌治疗。照射使用 6 MV X 射线断层调强放疗，单次剂量为 10 Gy。
共分析了 140 个剂量计。对测量的剂量应用温度校正系数后，所有剂量计的全局分析显示，计算剂量与测量剂量之间存在显著差异（P<0.001）。对于骨骼、软组织、皮肤和腔组的剂量计，这种差异也具有统计学意义（每组 P<0.001）。在全局分析中，测量的剂量平均值比计算的剂量平均值低 21.9%，而骨骼、软组织、皮肤和腔组的测量剂量平均值分别低 17.0%、21.2%、33.0%和 19.0%。
这项研究表明，所接受的剂量明显低于计算的剂量，并表明需要提高对这种差异的理解。
