The importance of mesorectum motion in determining PTV margins in rectal cancer patients treated with neoadjuvant radiotherapy
The importance of mesorectum motion in determining PTV margins in rectal cancer patients treated with neoadjuvant radiotherapy
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DOI：
10.1093/jrr/rrz092
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发表时间：
2020-03-01
影响因子：
2
通讯作者：
Gorken, Ilknur Bilkay
中科院分区：
文献类型：
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作者：
Alickikus, Zumre Arican;Kuru, Ahmet;Gorken, Ilknur Bilkay
新的精准放射治疗 (RT) 技术减少了定位软肿瘤和移动肿瘤的不确定性。然而，还有很多无法控制的内脏运动。在我们的研究中，对接受直肠癌新辅助放化疗（NA-CRT）的患者进行了评估，以确定分次间直肠系膜运动和剂量变化。该分析纳入了 2014 年至 2016 年间接受 NA-CRT 治疗直肠癌的 14 名患者。通过计划计算机断层扫描 (CT) 和锥形束 CT (CB-CT) 扫描描绘直肠系膜和临床靶区 (CTV)。在制定容量调节弧治疗 (VMAT) 计划后，对所有 CB-CT 进行了重新计划。最后，与最初的 CT 和 VMAT 计划相比，在所有 CB-CT 中评估了 PTV 和直肠系膜的体积和剂量变化。与初始 CT 相比，CB-CT 中直肠系膜体积的几何中心在 x、y 和 z 轴上分别移动了 1 (0.2-6.6)、1.6 (0.2-3.8) 和 1.6 (0-4.9) mm。 CB-CT 上的 PTV 剂量学参数（包括 D2、D95 和 D98）显示中位数为 47.19（46.70-47.80）、45.05（44.18-45.68）和 44.69（43.83-45.48）Gy，中位数为 1%（1-2）、0%（0-2）和 1%（0-2）与最初的 VMAT 计划相比，剂量变化。在我们的研究中，我们发现，在放疗期间，直肠系膜在横向和前后方向上移动了 20 毫米，在上/下方向上移动了近 10 毫米，导致剂量学参数的中值变化约为 2%。因此，在确定 PTV 裕度时必须考虑这些变化，以避免剂量变化。
New precision radiotherapy (RT) techniques reduce the uncertainties in localizing soft and moving tumors. However, there are still many uncontrollable internal organ movements. In our study, patients who underwent neoadjuvant chemoradiotherapy (NA-CRT) for rectal cancer were evaluated to determine inter-fraction mesorectum motion and dosimetric changes. Fourteen patients treated with NA-CRT for rectal cancer between 2014 and 2016 were included in the analysis. The mesorectum and clinical target volume (CTV) were delineated on planning computed tomography (CT) and cone-beam CT (CB-CT) scans. After planning with a volumetric modulated arc therapy (VMAT) plan, re-planning was performed on all CB-CTs. Finally, the volumetric and dosimetric changes of PTV and mesorectum were evaluated in all CB-CTs compared with the initial CT and VMAT plans. The geometrical center of mesorectum volume in CB-CTs had moved 1 (0.2-6.6), 1.6 (0.2-3.8) and 1.6 (0-4.9) mm in the x, y and z-axis respectively compared with the initial CT. The dosimetric parameters of PTV including D2, D95 and D98 on CB-CT showed a median 47.19 (46.70-47.80), 45.05 (44.18-45.68) and 44.69 (43.83-45.48) Gy and median 1% (1-2), 0% (0-2) and 1% (0-2) dosimetric change compared with the initial VMAT plan. In our study, we have shown that the mesorectum has moved up to 20 mm in the lateral and anterior-posterior direction and almost 10 mm in the superior/inferior direction during RT, causing a median of similar to 2% change in dosimetric parameters. Therefore, these movements must be considered in determining PTV margins to avoid dosimetric changes.