Real-Time Iterative Monitoring of Radiofrequency Ablation Tumor Therapy with ¹⁵O-Water PET Imaging

Abstract

A method that provides real-time image-based monitoring of solid tumor therapy to ensure complete tumor eradication during image-guided interventional therapy would be a valuable tool. The short, 2-min half-life of 15 O makes it possible to perform repeated PET imaging at 20-min intervals at multiple time points before and after image-guided therapy. In this study, 15 O-water PET was evaluated as a tool to provide real-time feedback and iterative image guidance to rapidly monitor the intratumoral coverage of radiofrequency (RF) ablation therapy. Methods: Tumor RF ablation therapy was performed on head and neck squamous cell carcinoma (SCC) xenograft tumors (length, ;23 mm) in 6 nude rats. The tumor in each animal was ablated with RF (1-cm active size ablation catheter, 70°C for 5 min) twice in 2 separate tumor regions with a 20-min separation. The 15 O-water PET images were acquired before RF ablation and after the first RF and second RF ablations using a small-animal PET scanner. In each PET session, approximately 100 MBq of 15 O-water in 1.0 mL of saline were injected intravenously into each animal. List-mode PET images were acquired for 7 min starting 20 s before injection. PET images were reconstructed by 2-dimensional ordered-subset expectation maximization into single-frame images and dynamic images at 10 s/frame. PET images were displayed and analyzed with software. Results: Pre-RF ablation images demonstrate that 15 O-water accumulates in tumors with 15 O activity reaching peak levels immediately after administration. After RF ablation, the ablated region had almost zero activity, whereas the unablated tumor tissue continued to have a high 15 O-water accumulation. Using image feedback, the RF probe was repositioned to a tumor region with residual 15 O-water uptake and then ablated. The second RF ablation in this new region of the tumor resulted in additional ablation of the solid tumor, with a corresponding decrease in activity on the 15 O-water PET image. Conclusion: 15 O-water PET clearly demonstrated the ablated tumor region, whereas the unablated tumor continued to show high 15 O-water accumulation. 15 O-water imaging shows promise as a tool for on-site, real-time monitoring of image-guided interventional cancer therapy.

Laser thermal therapy monitoring using complex differential variance in optical coherence tomography

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Interventional Molecular Imaging

“…The split-dose approach with a long procedure time allows for a potential second dose. However, a tracer with a shorter half-life (such as 11 C) would be more ideal, as it would allow for multiple doses and assessments throughout the treatment procedure without the confounding effect of remaining activity from earlier doses (29). …”

Cancer imaging: novel concepts in clinical magnetic resonance imaging

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