18F-FLT PET/CT for Early Response Monitoring and Dose Escalation in Oropharyngeal Tumors

Journal of Nuclear Medicine

Wim J.G. Oyen¹  Johannes H.A.M. Kaanders¹  Aswin L. Hoffmann¹  Esther G.C. Troost¹  Johan Bussink¹  Otto C. Boerman¹ 

关键词: ¹⁸F-fluorothymidine-PET;    head and neck cancer;    early response monitoring;    adaptive radiotherapy;    dose escalation;   

DOI  :  10.2967/jnumed.109.069310

学科分类：医学（综合）

来源: Society of Nuclear Medicine

【 摘 要 】

Accelerated tumor cell proliferation is an important mechanism adversely affecting therapeutic outcome in head and neck cancer. 3′-deoxy-3′-18F-fluorothymidine (18F-FLT) is a PET tracer to noninvasively image tumor cell proliferation. The aims of this study were to monitor early tumor response based on repetitive 18F-FLT PET/CT scans and to identify subvolumes with high proliferative activity eligible for dose escalation. Methods: Ten patients with oropharyngeal tumors underwent an 18F-FLT PET/CT scan before and twice during radiotherapy. The primary tumor and metastatic lymph nodes (gross tumor volume, or GTV) were delineated on CT (GTVCT) and after segmentation of the PET signal using the 50% isocontour of the maximum signal intensity or an adaptive threshold based on the signal-to-background ratio (GTVSBR). GTVs were calculated, and similarity between GTVCT and GTVSBR was assessed. Within GTVSBR, the maximum and mean standardized uptake value (SUVmax and SUVmean, respectively) was calculated. Within GTVCT, tumor subvolumes with high proliferative activity based on the 80% isocontour (GTV80%) were identified for radiotherapy planning with dose escalation. Results: The GTVCT decreased significantly in the fourth week but not in the initial phase of treatment. SUVmax and SUVmean decreased significantly as early as 1 wk after therapy initiation and even further before the fourth week of treatment. For the primary tumor, the average (±SD) SUVmean of the GTVSBR was 4.7 ± 1.6, 2.0 ± 0.9, and 1.3 ± 0.2 for the consecutive scans (P < 0.0001). The similarity between GTVCT and GTVSBR decreased during treatment, indicating an enlargement of GTVSBR outside GTVCT caused by the increasing difficulty of segmenting tracer uptake in the tumor from the background and by proliferative activity in the nearby tonsillar tissue. GTV80% was successfully identified in all primary tumors and metastatic lymph nodes, and dose escalation based on the GTV80% was demonstrated to be technically feasible. Conclusion: 18F-FLT is a promising PET tracer for imaging tumor cell proliferation in head and neck carcinomas. Signal changes in 18F-FLT PET precede volumetric tumor response and are therefore suitable for early response assessment. Definition of tumor subvolumes with high proliferative activity and dose escalation to these regions are technically feasible.

【 授权许可】

Unknown