Radiation Oncology Department, 3rd Affiliated Hospital of Qiqihar Medical University, Qiqihar, China.
Radiation Oncology Department, Fox Chase Cancer Center, Philadelphia, PA, United States.
Phys Med. 2020 Aug;76:142-149. doi: 10.1016/j.ejmp.2020.06.026. Epub 2020 Jul 14.
This work investigates the time and frequency to observe fiducial markers in MLC-modulated fields during intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) beam delivery for real-time prostate localization.
Thirty seven prostate patients treated with IMRT or VMAT were included in this retrospective study. DRR images were generated for all MLC segments/control points using the TPS. The MLC leaf pattern of each control point was overlaid on the DRR, and the number of fiducials within the MLC opening was analyzed. EPID images of fiducials in a pelvic phantom were obtained to demonstrate the fiducial visibility during modulated beam delivery.
Gold fiducials were visible on EPID images. The probability of seeing a number of fiducials within the MLC opening was analyzed. At least one fiducial was visible during 42 ± 2% and 52 ± 2% beam-on time for IMRT of the prostate with and without lymph nodes, and during 81 ± 4% and 80 ± 5% beam-on time for VMAT of the prostate with and without lymph nodes, respectively. The mean time interval to observe at least one fiducial was 8.4 ± 0.7 and 5.9 ± 0.5 s for IMRT of the prostate with and without the lymph nodes, respectively, and 1.6 ± 0.1 s for VMAT prostate patients. The estimated potential dosimetric uncertainty was 7% and 2% for IMRT and VMAT, respectively.
Our results demonstrated that the time and frequency to observe fiducial markers in MLC-modulated fields during IMRT/VMAT beam delivery were adequate for real-time prostate localization. The beam's eye view fiducial positions could be used for intrafractional target monitoring and motion correction in prostate radiotherapy.
本研究旨在探讨在调强放疗（IMRT）和容积调强弧形治疗（VMAT）中，观察调强射野中基准标记的时间和频率，以实现实时前列腺定位。
本回顾性研究纳入了 37 例接受 IMRT 或 VMAT 治疗的前列腺癌患者。所有调强子野/控制点均使用治疗计划系统（TPS）生成数字重建影像（DRR）。将每个控制点的调强叶片模式叠加在 DRR 上，分析调强叶片开口内的基准标记数量。在盆腔模体上获取 EPID 图像，以显示调强射束传输过程中基准标记的可见性。
金基准标记在 EPID 图像上可见。分析了在调强叶片开口内可见一定数量基准标记的概率。对于无淋巴结和有淋巴结的前列腺 IMRT，在 42±2%和 52±2%的射束开启时间内，至少有一个基准标记可见；对于无淋巴结和有淋巴结的前列腺 VMAT，在 81±4%和 80±5%的射束开启时间内，至少有一个基准标记可见。观察至少一个基准标记的平均时间间隔分别为无淋巴结和有淋巴结的前列腺 IMRT 的 8.4±0.7s 和 5.9±0.5s，以及前列腺 VMAT 的 1.6±0.1s。估计的潜在剂量不确定性分别为 IMRT 和 VMAT 的 7%和 2%。
我们的结果表明，在 IMRT/VMAT 射束传输过程中观察调强叶片野中基准标记的时间和频率足以实现实时前列腺定位。视线基准标记位置可用于前列腺放疗中的分次内靶区监测和运动校正。
