van der Horst Astrid, Houweling Antonetta C, van Tienhoven Geertjan, Visser Jorrit, Bel Arjan
Department of Radiation Oncology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands.
J Appl Clin Med Phys. 2017 Nov;18(6):142-151. doi: 10.1002/acm2.12199. Epub 2017 Oct 4.
Pancreatic tumors show large interfractional position variation. In addition, changes in gastrointestinal gas volumes and body contour take place over the course of radiation therapy. We aimed to quantify the effect of these anatomical changes on target dose coverage, for the clinically used fiducial marker-based patient position verification and, for comparison, also for simulated bony anatomy-based position verification. Nine consecutive patients were included in this retrospective study. To enable fraction dose calculations on cone-beam CT (CBCT), the planning CT was deformably registered to each CBCT (13-15 per patient); gas volumes visible on CBCT were copied to the deformed CT. Fraction doses were calculated for the clinically used 10 MV VMAT treatment plan (with for the planning target volume (PTV): D = 95%), according to fiducial marker-based and bony anatomy-based image registrations. Dose distributions were rigidly summed to yield the accumulated dose. To evaluate target dose coverage, we defined an iCTV volume, i.e., the internal clinical target volume (iCTV) expanded with a 5 mm margin to account for remaining uncertainties including delineation uncertainties. We analyzed D , D , and D for iCTV and PTV (i.e., iCTV plus 10 mm margin). We found that for fiducial marker-based registration, differences between fraction doses and planned dose were minimal. For bony anatomy-based registration, fraction doses differed considerably, resulting in large differences between planned and accumulated dose for some patients, up to a decrease in D of the iCTV from 95.9% to 85.8%. Our study shows that fractionated photon irradiation of pancreatic tumors is robust against variations in body contour and gastrointestinal gas, with dose coverage only mildly affected. However, as a result of interfractional tumor position variations, target dose coverage can severely decline when using bony anatomy for patient position verification. Therefore, the use of intratumoral fiducial marker-based daily position verification is essential in pancreatic cancer patients.
胰腺肿瘤在分次治疗期间显示出较大的位置变化。此外，胃肠道气体量和身体轮廓在放射治疗过程中会发生改变。我们旨在量化这些解剖学变化对靶区剂量覆盖的影响，既针对临床使用的基于基准标记的患者体位验证，也为作比较针对模拟的基于骨骼解剖的体位验证。本回顾性研究纳入了9例连续患者。为了能够在锥形束CT（CBCT）上进行分次剂量计算，将计划CT与每个CBCT进行变形配准（每位患者13 - 15次）；将CBCT上可见的气体量复制到变形后的CT上。根据基于基准标记和基于骨骼解剖的图像配准，针对临床使用的10MV容积调强弧形治疗（VMAT）计划（计划靶区（PTV）：D = 95%）计算分次剂量。将剂量分布进行刚性求和以得出累积剂量。为了评估靶区剂量覆盖情况，我们定义了一个内部临床靶区（iCTV）体积，即内部临床靶区（iCTV）向外扩展5mm边界以考虑包括勾画不确定性在内的剩余不确定性。我们分析了iCTV和PTV（即iCTV加10mm边界）的D 、D 和D 。我们发现，对于基于基准标记的配准，分次剂量与计划剂量之间的差异最小。对于基于骨骼解剖的配准，分次剂量差异很大，导致一些患者计划剂量与累积剂量之间存在很大差异，iCTV的D 降低幅度高达从95.9%降至85.8%。我们的研究表明，胰腺肿瘤的分次光子照射对身体轮廓和胃肠道气体的变化具有鲁棒性，剂量覆盖仅受到轻微影响。然而，由于分次治疗期间肿瘤位置的变化，在使用骨骼解剖进行患者体位验证时，靶区剂量覆盖可能会严重下降。因此，对于胰腺癌患者，使用基于瘤内基准标记的每日体位验证至关重要。
