Corriher Taylor J, Dutta Sunil W, Alonso Clayton E, Libby Bruce, Romano Kara D, Showalter Timothy N
Department of Radiation Oncology, University of Virginia, Charlottesville, Virginia, USA.
J Contemp Brachytherapy. 2020 Jun;12(3):279-282. doi: 10.5114/jcb.2020.96871. Epub 2020 Jun 30.
For cervical brachytherapy planning, magnetic resonance imaging (MRI) is preferable to computed tomography (CT) for target delineation. However, due to logistical and financial restrictions, in-room MRI is sometimes not routinely available in brachytherapy centers. Our institution has created a workflow that integrates MRI-based target delineation with an in-room CT scanner, with the aim of improving target coverage and conformality. This study reports the initial dosimetric results with using this workflow.
A retrospective review was performed on 46 consecutive patients who received definitive chemoradiation with 5 fraction intracavitary high-dose-rate (HDR) brachytherapy for cervical cancer. Fraction 1 was planned from CT only. Outpatient MRI was obtained after Smit sleeve placement and first insertion to assess concurrent chemoradiotherapy tumor response. This MRI was registered to the CT for planning fractions 2-5. The median prescription dose for the cohort was 25 Gy (range, 25-29 Gy).
The D to the high-risk clinical target volume (HR-CTV) and D rectal dose were increased from fraction 1 to fraction 2-5 averaged ( < 0.05). Among the 18 patients with complete volumetric data, there was no significant difference in HR-CTV size, with an average decrease of 1.73 cc ( > 0.05) with MRI fusion. Eleven out of 18 patients had changes in high-risk target volume greater than 20%, with an absolute average change in volume of 31.5%.
The use of asynchronous MRI for target delineation, with co-registration to CT for each fraction of brachytherapy was associated with higher D to the HR-CTV. We observed slightly higher D rectal doses with MRI, but cumulative rectal doses were within accepted thresholds. High-risk target volumes were not consistently increased or decreased, but MRI fusion was associated with target volume changes greater than 20% in over half of the treated patients.
在宫颈癌近距离治疗计划中，磁共振成像（MRI）在靶区勾画方面优于计算机断层扫描（CT）。然而，由于后勤和资金限制，近距离治疗中心有时无法常规使用室内MRI。我们机构创建了一种工作流程，将基于MRI的靶区勾画与室内CT扫描仪相结合，旨在提高靶区覆盖范围和适形性。本研究报告了使用该工作流程的初步剂量学结果。
对46例连续接受确定性放化疗联合5次腔内高剂量率（HDR）近距离治疗宫颈癌的患者进行回顾性研究。第1次分割仅根据CT进行计划。在放置施密特套管并首次插入后获得门诊MRI，以评估同步放化疗的肿瘤反应。将该MRI与CT进行配准，用于计划第2 - 5次分割。该队列的中位处方剂量为25 Gy（范围，25 - 29 Gy）。
从第1次分割到第2 - 5次分割平均而言，高危临床靶区（HR-CTV）的剂量（D）和直肠剂量增加（<0.05）。在18例有完整体积数据的患者中，HR-CTV大小无显著差异，MRI融合后平均减少1.73 cc（>0.05）。18例患者中有11例高危靶区体积变化大于20%，体积绝对平均变化为31.5%。
使用异步MRI进行靶区勾画，并在每次近距离治疗分割时与CT进行配准，与HR-CTV的较高剂量（D）相关。我们观察到MRI的直肠剂量略高，但累积直肠剂量在可接受阈值范围内。高危靶区体积并非持续增加或减少，但MRI融合与超过半数治疗患者中大于20%的靶区体积变化相关。
