Tyyger Marcus, Bhaumik Suchandana, Nix Michael, Currie Stuart, Nallathambi Chandran, Speight Richard, Al-Qaisieh Bashar, Murray Louise
Leeds Cancer Centre, Leeds Teaching Hospitals NHS Trust, Leeds, UK.
Department of Neuroradiology, Leeds Teaching Hospitals NHS Trust, Leeds, UK.
BJR Open. 2021 Nov 26;3(1):20210067. doi: 10.1259/bjro.20210067. eCollection 2021.
Glioblastoma (GBM) radiotherapy (RT) target delineation requires MRI, ideally concurrent with CT simulation (pre-RT MRI). Due to limited MRI availability, <72 h post-surgery MRI is commonly used instead. Whilst previous investigations assessed volumetric differences between post-surgical and pre-RT delineations, dosimetric impact remains unknown. We quantify volumetric and dosimetric impact of using post-surgical MRI for GBM target delineation.
Gross tumour volumes (GTVs) for five GBM patients receiving chemo-RT with post-surgical and pre-RT MRIs were delineated by three independent observers. Planning target volumes (PTVs) and RT plans were generated for each GTV. Volumetric and dosimetric differences were assessed through: absolute volumes, volume-distance histograms and dose-volume histogram statistics.
Post-surgical MRI delineations had significantly ( < 0.05) larger GTV and PTV volumes (median 16.7 and 64.4 cm respectively). Post-surgical RT plans, applied to pre-RT delineations, had significantly decreased ( < 0.01) median PTV doses (ΔD99% = -8.1 Gy and ΔD95% = -2.0 Gy). Median organ-at-risk (OAR) dose increases (brainstem ΔD5% =+0.8, normal brain mean dose =+2.9 and normal brain ΔD10% = 5.3 Gy) were observed.
Post-surgical MRI delineation significantly impacted RT planning, with larger normal-appearing tissue volumes irradiated and increased OAR doses, despite a reduced coverage of the pre-RT defined target.
We believe this is the first investigation assessing the dosimetric impact of using post-surgical MRI for GBM target delineation. It highlights the potential of significantly degraded RT plans, showing the clinical need for dedicated MRI for GBM RT.
胶质母细胞瘤（GBM）放疗（RT）靶区勾画需要MRI，理想情况下是与CT模拟同时进行（放疗前MRI）。由于MRI设备有限，通常使用术后<72小时的MRI替代。虽然之前的研究评估了术后和放疗前勾画的体积差异，但剂量学影响仍不清楚。我们量化了使用术后MRI进行GBM靶区勾画的体积和剂量学影响。
由三名独立观察者勾画五名接受化疗放疗的GBM患者术后和放疗前MRI的大体肿瘤体积（GTV）。为每个GTV生成计划靶体积（PTV）和放疗计划。通过绝对体积、体积-距离直方图和剂量-体积直方图统计评估体积和剂量学差异。
术后MRI勾画的GTV和PTV体积显著更大（<0.05）（中位数分别为16.7和64.4 cm）。应用于放疗前勾画的术后放疗计划，PTV中位剂量显著降低（<0.01）（ΔD99%=-8.1 Gy，ΔD95%=-2.0 Gy）。观察到中位危及器官（OAR）剂量增加（脑干ΔD5%=+0.8，正常脑平均剂量=+2.9，正常脑ΔD10%=5.3 Gy）。
术后MRI勾画对放疗计划有显著影响，尽管放疗前定义的靶区覆盖减少，但照射的正常组织体积更大，OAR剂量增加。
我们认为这是首次评估使用术后MRI进行GBM靶区勾画的剂量学影响的研究。它突出了放疗计划显著退化的可能性，显示了GBM放疗专用MRI的临床需求。
