Christensen Michael, Kamson David Olayinka, Snyder Michael, Kim Harold, Robinette Natasha L, Mittal Sandeep, Juhász Csaba
Department of Radiation Oncology, Barbara Ann, Karmanos Cancer Center, Wayne State University School of Medicine, 540 E. Canfield, Detroit, MI 48201, USA. Barbara Ann Karmanos Cancer Institute, Detroit, MI, USA.
Departments of Pediatrics and Neurology, Wayne State University School of Medicine, Detroit, MI, USA. PET Center and Translational Imaging Laboratory, Children's Hospital of Michigan, Detroit, MI, USA.
J Radiat Oncol. 2014 Jun;3(2):131-138. doi: 10.1007/s13566-013-0132-5.
Glioblastoma is an infiltrative malignancy that tends to extend beyond the MRI-defined tumor volume. We utilized positron emission tomography (PET) imaging with the radiotracer alpha-[C]methyl-L -tryptophan (AMT) to develop a reliable high-risk gross tumor volume (HR-GTV) method for delineation of glioblastoma. AMT can detect solid tumor mass and tumoral brain infiltration by increased tumoral tryptophan transport and metabolism via the immunosuppressive kynurenine pathway.
We reviewed all patients in our database with histologically proven glioblastoma who underwent preoperative AMT-PET scan prior to surgery and chemoradiation. Treated radiotherapy volumes were derived from the simulation CT with MRI fusion. High-GTV with contrast enhanced T1-weighted MRI alone (GTV) was defined as the postoperative cavity plus any residual area of enhancement on postcontrast T1-weighted images. AMT-PET images were retrospectively fused to the simulation CT, and a high-risk GTVs generated by both AMT-PET alone (GTV) was defined using a threshold previously established to distinguish tumor tissue from peritumoral edema. A composite volume of MRI and AMT tumor volume was also created (combination of MRI fused with AMT-PET data; GTV). In patients with definitive radiographic progression, follow-up MRI demonstrating initial tumor progression was fused with the pretreatment images and a progression volume was contoured. The coverage of the progression volume by GTV, GTV, and GTV was determined and compared using the Wilcoxon's signed-rank test.
Eleven patients completed presurgical AMT-PET scan, seven of whom had progressive disease after initial therapy. GTV (mean, 50.2 cm) and GTV (mean, 48.9 cm) were not significantly different. Mean concordance index of the volumes was 39±15 %. Coverage of the initial recurrence volume by HR-GTV (mean, 52 %) was inferior to both GTV (mean, 68 %; =0.028) and GTV (mean 73 %; =0.018). The AMT-PET-exclusive coverage was up to 41 % of the recurrent volume. There was a tendency towards better recurrence coverage with GTV than with GTV alone ( =0.068). Addition of 5 mm concentric margin around GTV, GTV, and GTV would have completely covered the initial progression volume in 14, 57, and 71 % of the patients, respectively.
We found that a GTV defined by AMT-PET produced similar volume, but superior recurrence coverage than the treated standard MRI-determined volume. A prospective study is necessary to fully determine the usefulness of AMT-PET for volume definition in glioblastoma radiotherapy planning.
胶质母细胞瘤是一种浸润性恶性肿瘤，往往超出MRI定义的肿瘤体积。我们利用正电子发射断层扫描（PET）成像与放射性示踪剂α-[C]甲基-L-色氨酸（AMT）来开发一种可靠的高危大体肿瘤体积（HR-GTV）方法，用于勾画胶质母细胞瘤。AMT可以通过免疫抑制犬尿氨酸途径增加肿瘤色氨酸转运和代谢来检测实体肿瘤肿块和肿瘤脑浸润。
我们回顾了数据库中所有经组织学证实为胶质母细胞瘤且在手术及放化疗前接受过术前AMT-PET扫描的患者。治疗放疗体积来自模拟CT与MRI融合图像。单纯对比增强T1加权MRI定义的高GTV（GTV）为术后腔隙加上对比增强T1加权图像上任何残留的强化区域。AMT-PET图像回顾性融合到模拟CT上，单独由AMT-PET生成的高危GTV（GTV）使用先前确定的阈值来定义，以区分肿瘤组织与瘤周水肿。还创建了MRI和AMT肿瘤体积的复合体积（MRI与AMT-PET数据融合；GTV）。在有明确影像学进展的患者中，将显示初始肿瘤进展的随访MRI与治疗前图像融合，并勾勒出进展体积。使用Wilcoxon符号秩检验确定并比较GTV、GTV和GTV对进展体积的覆盖情况。
11例患者完成了术前AMT-PET扫描，其中7例在初始治疗后病情进展。GTV（平均50.2 cm）和GTV（平均48.9 cm）无显著差异。体积的平均一致性指数为39±15%。HR-GTV（平均52%）对初始复发体积的覆盖低于GTV（平均68%；P=0.028）和GTV（平均73%；P=0.018）。仅AMT-PET的覆盖范围高达复发体积的41%。GTV对复发的覆盖有优于单独GTV的趋势（P=0.068）。在GTV、GTV和GTV周围添加5 mm同心边缘将分别在14%、57%和71%的患者中完全覆盖初始进展体积。
我们发现，由AMT-PET定义的GTV产生的体积相似，但对复发的覆盖优于治疗标准MRI确定的体积。需要进行前瞻性研究以充分确定AMT-PET在胶质母细胞瘤放疗计划中体积定义的有用性。
