Estimation of volumes of distribution and intratumoral ethanol concentrations by computed tomography scanning after percutaneous ethanol injection

Impact of Injection-Based Delivery Parameters on Local Distribution Volume of Ethyl-Cellulose Ethanol Gel in Tissue and Tissue Mimicking Phantoms

OBJECTIVE

Local drug delivery aims to minimize systemic toxicity by preventing off-target effects; however, injection parameters influencing depot formation of injectable gels have yet to be thoroughly studied. We explored the effects of needle characteristics, injection depth, rate, volume, and polymer concentration on gel ethanol distribution in both tissue and phantoms.

METHODS

The polymer ethyl cellulose (EC) was added to ethanol to form an injectable gel to ablate cervical precancer and cancer. Tissue mimicking phantoms composed of 1% agarose dissolved in deionized water were used to establish overall trends between various injection parameters and the resulting gel distribution. Additional experiments were performed in excised swine cervices with a CT-imageable injectate formulation, which enabled visualization of the distribution without tissue sectioning.

RESULTS

Needle type and injection rate had minimal impact on gel distribution, while needle depths ≥13 mm yielded significantly larger distributions. Needle gauge and EC concentration impacted injection pressure with maximum gel distribution achieved when the pressure was 70-250 kPa. Injection volumes ≤3 mL of 6% EC-ethanol minimized fluid leakage away from the injection site. Results guided the development of a speculum-compatible hand-held injector to deliver gel ethanol into the cervix.

CONCLUSION

Needle depth, gauge, and polymer concentration are critical to consider when delivering injectable gels.

SIGNIFICANCE

This study addressed key questions related to the impact of injection-based parameters on gel distribution at a scale relevant to human applications including: 1) how best to deliver EC-ethanol into the cervix and 2) general insights about injection protocols relevant to the delivery of injectable gels in tissue.

Radiologic-pathologic analysis of increased ethanol localization and ablative extent achieved by ethyl cellulose

Ethanol provides a rapid, low-cost ablative solution for liver tumors with a small technological footprint but suffers from uncontrolled diffusion in target tissue, limiting treatment precision and accuracy. Incorporating the gel-forming polymer ethyl cellulose to ethanol localizes the distribution. The purpose of this study was to establish a non-invasive methodology based on CT imaging to quantitatively determine the relationship between the delivery parameters of the EC-ethanol formulation, its distribution, and the corresponding necrotic volume. The relationship of radiodensity to ethanol concentration was characterized with water-ethanol surrogates. Ex vivo EC-ethanol ablations were performed to optimize the formulation (n = 6). In vivo ablations were performed to compare the optimal EC-ethanol formulation to pure ethanol (n = 6). Ablations were monitored with CT and ethanol distribution volume was quantified. Livers were removed, sectioned and stained with NADH-diaphorase to determine the ablative extent, and a detailed time-course histological study was performed to assess the wound healing process. CT imaging of ethanol-water surrogates demonstrated the ethanol concentration-radiodensity relationship is approximately linear. A concentration of 12% EC in ethanol created the largest distribution volume, more than eight-fold that of pure ethanol, ex vivo. In vivo, 12% EC-ethanol was superior to pure ethanol, yielding a distribution volume three-fold greater and an ablation zone six-fold greater than pure ethanol. Finally, a time course histological evaluation of the liver post-ablation with 12% EC-ethanol and pure ethanol revealed that while both induce coagulative necrosis and similar tissue responses at 1-4 weeks post-ablation, 12% EC-ethanol yielded a larger ablation zone. The current study demonstrates the suitability of CT imaging to determine distribution volume and concentration of ethanol in tissue. The distribution volume of EC-ethanol is nearly equivalent to the resultant necrotic volume and increases distribution and necrosis compared to pure ethanol.

Comparison of Methods for Surface Modification of Barium Titanate Nanoparticles for Aqueous Dispersibility: Toward Biomedical Utilization of Perovskite Oxides

Colloidal perovskite barium titanate (BaTiO3, or BT) nanoparticles (NPs), conventionally used for applications in electronics, can also be considered for their potential as biocompatible computed tomography (CT) contrast agents. NPs of BT produced by traditional solid-state methods tend to have broad size distributions and poor dispersibility in aqueous media. Furthermore, uncoated BT NPs can be cytotoxic because of leaching of the heavy metal ion, Ba2+. Here, we present and compare three approaches for surface modification of BT NPs (8 nm) synthesized by the gel collection method to improve their aqueous stability and dispersibility. The first approach produced citrate-capped BT NPs that exhibited extremely high aqueous dispersibility (up to 50 mg/mL) and a small hydrodynamic size (11 nm). Although the high dispersibility was found to be pH-dependent, such aqueous stability sufficiently enabled a feasibility analysis of BT NPs as CT contrast agents. The second approach, a core/shell design, aimed to encapsulate BT nanoaggregates with a silica layer using a modified Stöber method. A cluster of 7-20 NPs coated with a thick layer (20-100 nm) of SiO2 was routinely observed, producing larger NPs in the 100-200 nm range. A third approach was developed using a reverse-microemulsion method to encapsulate a single BT core within a thin (10 nm) silica layer, with an overall particle size of 29 nm. The -OH groups on the silica layer readily enabled surface PEGylation, allowing the NPs to remain highly stable in saline solutions. We report that the silica-coated BT NPs in both methods exhibited a low level of Ba2+ leaching (≤3% of total barium in NPs) in phosphate-buffered saline for 48 h compared to the unmodified BT NPs (14.4%).

Synergy in cancer treatment between liposomal chemotherapeutics and thermal ablation

Minimally invasive image-guided tumor ablation using short duration heating via needle-like applicators using energies such as radiofrequency or microwave has seen increasing clinical use to treat focal liver, renal, breast, bone, and lung tumors. Potential benefits of this thermal therapy include reduced morbidity and mortality compared to standard surgical resection and ability to treat non-surgical patients. However, improvements to this technique are required as achieving complete ablation in many cases can be challenging particularly at margins of tumors>3 cm in diameter and adjacent to blood vessels. Thus, one very promising strategy has been to combine thermal tumor ablation with adjuvant nanoparticle-based chemotherapy agents to improve efficiency. Here, we will primarily review principles of thermal ablation to provide a framework for understanding the mechanisms of combination therapy, and review the studies on combination therapy, including presenting preliminary data on the role of such variables as nanoparticle size and thermal dose on improving combination therapy outcome. We will discuss how thermal ablation can also be used to improve overall intratumoral drug accumulation and nanoparticle content release. Finally, in this article we will further describe the appealing off-shoot approach of utilizing thermal ablation techniques not as the primary treatment, but rather, as a means to improve efficiency of intratumoral nanoparticle drug delivery.

Tissue Chemoablation

PURPOSE

To provide an overview of the state of the art of tissue chemoablation in animal and human organs and cancers. We also describe our experience with the feasibility, predictability, and reproducibility of necrosis produced by needle chemoablative therapies including ethanol, hypertonic saline, and acetic acid solutions as well as gels in a porcine renal model.

MATERIALS AND METHODS

A MEDLINE search was performed for articles on animal and human tissue chemoablation published since 1965. In addition, at Washington University, experimental chemoablation was performed in pigs with 95% ethanol (4 mL), 24% hypertonic saline (4 mL), or 50% acetic acid (4 mL) solutions as well as in gel form.

RESULTS

There is extensive literature on the use of chemoablation for liver metastases; recently, chemoablation of the prostate has become an area of research. Human studies have been limited to patients who are not surgical candidates or to investigational procedures performed prior to definitive prostatic surgery. Animal studies of renal chemoablation as a sole therapy have produced mixed results. In our studies, only acetic acid provided complete necrosis.

CONCLUSIONS

To date, ethanol chemoablation has been shown to be feasible and reproducible only for metastatic hepatic carcinoma. In urology, chemoablation is still very much in the investigational stage for both the prostate and the kidney. A significant drawback is that even in the gel form, the spread of the chemoablative substance through the tissue is irregular and unpredictable. In the future, chemoablation may become a more effective modality by combining it with radiofrequency or other energy sources.

Study design for concurrent development, assessment, and implementation of new diagnostic imaging technology

With current constraints on health care resources and emphasis on value for money, new diagnostic imaging technologies must be assessed and their value demonstrated. The state of the art in the field of diagnostic imaging technology assessment advocates a hierarchical step-by-step approach. Although rigorous, such a hierarchical assessment is time-consuming, and, given the current rapid advances in technology, results are often too late to influence management and policy decisions. The purpose of this article is to discuss a study design in which development, assessment, and implementation of new diagnostic imaging technology take place concurrently in one integrated process. An empirically based pragmatic study design is proposed for imaging technology assessment. To minimize bias and enable comparison with current technology, a randomized controlled design is used whenever feasible and ethical. Outcome measures should reflect the clinical decision-making process based on imaging information and acceptance of the new test. Outcome measures can include additional imaging studies requested, costs of diagnostic work-up and treatment, physicians' confidence in therapeutic decision making, recruitment rate, and patient outcome measures related to the clinical problem. The key feature of the proposed study design is analysis of trends in outcome measures over time.

Quantitative methods for indirect CT lymphography

In this investigation, we applied quantitative CT methods to characterize contrast enhanced lymph nodes opacified using iodinated contrast media for indirect CT lymphography. Iodinated nanoparticles were injected into the buccal submucosa and SQ into the metatarsus and metacarpus of four normal swine (1.0-4.0 ml/site, 76 mg I/ml). Attenuation (HU), volume (cm3), iodine concentration (mg I/cm3), total iodine uptake (mg I), contrast-to-noise ratio (CNR), and percent injected dose (%ID) were estimated in opacified inguinal, cervical and parotid/mandibular lymph nodes using manual image segmentation techniques on 24 hour post-contrast CT images. Lymph node volumes estimated by multiple slice ROI analysis were compared with estimates obtained by post-excisional weight measurements. HU and iodine concentration increased 5-20 fold in opacified nodes (p < 0.01) and CNR increased more than four-fold (p < 0.001). %ID ranged between 3.5 and 11.9% and did not appear dose related. ROI estimated lymph node volumes approximated volumes calculated from weight measurements. (R2 = 0.94, p < 0.0001). We conclude that interstitially injected iodinated nanoparticles increase attenuation and conspicuity of targeted nodes on CT images. Quantitative methods could play an important clinical role in more accurate metastasis detection.