Radiofrequency Ablation

Abstract

Rationale and Objectives Inflammatory reaction surrounding the ablated area is a major confounding factor in the early detection of viable tumor after radiofrequency (RF) ablation. A difference in the responsiveness of normal and tumor blood vessels to vasoactive agents may be used to distinguish these regions in post-ablation follow-up. The goal of this study was to examine longitudinal perfusion changes in untreated viable tumor and the peripheral hyperemic rim of RF-ablated tumor in response to a vasoconstrictor (phenylephrine) or vasodilator (hydralazine) in a subcutaneous rat tumor model. Materials and Methods Bilateral subcutaneous shoulder tumors were inoculated in 24 BDIX rats and evenly divided into two groups (phenylephrine and hydralazine groups). One tumor in each animal was completely treated with RF ablation (at 90 ± 2°C for 3 minutes), and the other remained untreated. Computed tomographic perfusion scans before and after phenylephrine (10 μg/kg) or hydralazine (5 mg/kg) administration were performed 2, 7, and 14 days after ablation. Four rats per group were euthanized on each scan day, and pathologic evaluation was performed. The changes of blood flow in the peripheral rim of ablated tumor and untreated viable tumor in response to phenylephrine or hydralazine at each time point were compared. The diagnostic accuracy of viable tumor using the percentage change of blood flow in response to phenylephrine and hydralazine was compared using receiver-operating characteristic analysis. Results The peripheral rim of ablated tumor presented with a hyperemic reaction with dilated vessels and congestion on day 2 after ablation, numerous inflammatory vessels on day 7, and granulation tissue formation on day 14. Phenylephrine significantly decreased the blood flow in the peripheral hyperemic rim of ablated tumor on days 2, 7, and 14 by 16.3±9.7% (P = .001), 24.0±22.6% (P = .007), and 31.1±25.4% (P = .045), respectively. In untreated viable tumor, the change in blood flow after phenylephrine was irregular and insignificant. Hydralazine decreased the blood flow in the peripheral rim of both ablated tumor and untreated viable tumor. Receiver-operating characteristic analysis showed that reliable tumor diagnosis using the percentage change of blood flow in response to phenylephrine was noted on days 2 and 7, for which the areas under the curve were 0.82 (95% confidence interval, 0.64–1.00) and 0.81 (95% confidence interval, 0.56–1.00), respectively. However, tumor diagnosis using the blood flow change in response to hydralazine was unreliable. Conclusion Phenylephrine markedly decreased blood flow in the peripheral hyperemic rim of ablated tumor but had little effect on the untreated viable tumor. Computed tomographic perfusion with phenylephrine may be useful in the long-term treatment assessment of RF ablation.

Differentiation of Benign Periablational Enhancement from Residual Tumor Following Radio-Frequency Ablation Using Contrast-Enhanced Ultrasonography in a Rat Subcutaneous Colon Cancer Model

“…We found blood volume and blood flow in BPE decreased on day 1 and increased on days 4 and 7 after ablation. Histology changes in the same tumor model on days 2 and 7 after RF ablation were reported in our previous study (Wu et al 2009). In short, the peripheral rim of ablated tumor presented with a hyperemic reaction with dilated vessels and congestion on day 2 after ablation and numerous inflammatory vessels and granulation tissue formation on day 7.…”

“…However, this border became less distinct over time. This is most likely due to the typical inflammatory response and granulation tissue formation after RF ablation (Wu et al 2009). However, it was difficult to differentiate BPE from residual tumor by visual judgment alone due to contrast enhancement in both regions.…”

Multimodal In Vivo Imaging Exposes the Voyage of Nanoparticles in Tumor Microcirculation

“…Furthermore, a critical liposome size exists below which active targeting substantially improves the intratumoral retention of nanoparticles, especially at slow blood flow regions. Thus, the use of an easily measured phenotypic biomarker (tumor blood flow) 41, 58, 59 could facilitate the selection of a specific set of different nanoparticles to maximize the overall deposition into a specific tumor. This implies that therapeutic regimens could be individualized to the regional hemodynamic profile of a patient’s tumor to maximize the drug deposition in a tumor not just on a patient-by-patient but on a region-by-region basis.…”

“…Even in these ‘controlled’ tumor models of the same cell type, stage, and tumor size, regions with very different blood flows were identified which varied widely in topology from one tumor to the next, which is consistent with previous studies. 40, 41 While nCE-μCT provided high resolutions, it only allowed to study the intratumoral deposition of a single liposome formulation. Therefore, we utilized small animal fluorescence imaging (FMT) to quantitatively and simultaneously image four different liposome formulations (labeled with a different NIR fluorophore) in the same tumor.…”

Shaping Cancer Nanomedicine: The Effect of Particle Shape on The In Vivo Journey of Nanoparticles

“…Indeed, it was recently shown that the intravascular and transvascular transport of nanoparticles in a tumor’s region is strongly governed by the relationship of particle size to the microvascular network and hemodynamics of that tumor’s region [38]. Given that tumors are heterogeneous in both hemodynamics and pathology [35, 39–44], a single “one-size-fits-all” nanoparticle design might not be the most effective approach. We suggest that the nanoparticle design depends on the exact location of interest (e.g.…”