Selvaraj Jothybasu, Baker Colin, Nahum Alan
Medical Physics and Radiation Engineering, The Canberra Hospital, Garran, Canberra, ACT, 2604, Australia.
Department of Physics, Clatterbridge Cancer Centre NHS Foundation Trust, Bebington, Wirral, CH63 4JY, UK.
Australas Phys Eng Sci Med. 2016 Jun;39(2):493-500. doi: 10.1007/s13246-016-0446-x. Epub 2016 May 11.
The impact of microscopic disease extension (MDE), extra-CTV tumour islets (TIs), incidental dose and dose conformity on tumour control probability (TCP) is analyzed using insilico simulations in this study. MDE in the region in between GTV and CTV is simulated inclusive of geometric uncertainties (GE) using spherical targets and spherical dose distribution. To study the effect of incidental dose on TIs and the effect of dose-response curve (DRC) on tumour control, islets were randomly distributed and TCP was calculated for various dose levels by rescaling the dose. Further, the impact of dose conformity on required PTV margins is also studied. The required PTV margins are ~2 mm lesser than assuming a uniform clonogen density if an exponential clonogen density fall off in the GTV-CTV is assumed. However, margins are almost equal if GE is higher in both cases. This shows that GE has a profound impact on margins. The effect of TIs showed a bi-phasic relation with increasing dose, indicating that patients with islets not in the beam paths do not benefit from dose escalation. Increasing dose conformity is also found to have considerable effect on TCP loss especially for larger GE. Further, smaller margins in IGRT should be used with caution where uncertainty in CTV definition is of concern.
本研究使用计算机模拟分析了微观疾病扩展（MDE）、CTV外肿瘤小岛（TIs）、偶然剂量和剂量适形性对肿瘤控制概率（TCP）的影响。使用球形靶区和球形剂量分布模拟GTV和CTV之间区域的MDE，包括几何不确定性（GE）。为了研究偶然剂量对TIs的影响以及剂量反应曲线（DRC）对肿瘤控制的影响，随机分布小岛，并通过重新缩放剂量计算不同剂量水平下的TCP。此外，还研究了剂量适形性对所需PTV边界的影响。如果假设GTV-CTV中克隆源密度呈指数下降，所需的PTV边界比假设克隆源密度均匀时小约2毫米。然而，如果两种情况下GE都较高，则边界几乎相等。这表明GE对边界有深远影响。TIs的影响显示出与剂量增加的双相关系，表明不在射线路径中的小岛患者无法从剂量增加中获益。还发现增加剂量适形性对TCP损失有相当大的影响，尤其是对于较大的GE。此外，在关注CTV定义存在不确定性的情况下，应谨慎使用IGRT中的较小边界。
