Understanding the intra-tumoral distribution of chemotherapeutic drugs is extremely important in predicting therapeutic outcome. Tissue mimicking gel phantoms are useful for studying drug distribution in vitro but quantifying distribution is laborious due to the need to section phantoms over the relevant time course and individually quantify drug elution. In this study we compare a bespoke version of the traditional phantom sectioning approach, with a novel confocal microscopy technique that enables dynamic in situ measurements of drug concentration. Release of doxorubicin from Drug-eluting Embolization Beads (DEBs) was measured in phantoms composed of alginate and agarose over comparable time intervals. Drug release from several different types of bead were measured. The non-radiopaque DC Bead™ generated a higher concentration at the boundary between the beads and the phantom and larger drug penetration distance within the release period, compared with the radiopaque DC Bead LUMI™. This is likely due to the difference of compositional and structural characteristics of the hydrogel beads interacting differently with the loaded drug. Comparison of in vitro results against historical in vivo data show good agreement in terms of drug penetration, when confounding factors such as geometry, elimination and bead chemistry were accounted for. Hence these methods have demonstrated potential for both bead and gel phantom validation, and provide opportunities for optimisation of bead design and embolization protocols through in vitro-in vivo comparison.

Topotecan is a camptothecin analogue with potential advantages over irinotecan for transarterial chemoembolization (TACE) of hepatic colorectal metastases including greater anti-neoplastic activity without enzymatic activation. The purpose of this study was to assess safety and tolerability of topotecan-loaded radiopaque microspheres (ROMTOP) administered by TACE in a rabbit model and to compare the in vitro elution of topotecan from microspheres to irinotecan. Topotecan was loaded into radiopaque microspheres (70–150 µm, DC Bead LUMI™, Biocompatibles UK Ltd—Boston Scientific Corporation) to the maximum capacity of 80 mg/mL of microspheres. Six healthy New Zealand White rabbits underwent hepatic TACE with ROMTOP under fluoroscopic guidance until angiographic stasis. Assessment of toxicities included regular liver function tests and complete blood counts until euthanasia 28 days post-TACE. In vitro topotecan elution from the microspheres was assessed using an open-loop flow-through system and compared to irinotecan. The mean bead volume and topotecan dose delivered were 0.086 mL (0.076–0.105 mL) and 1.99 mg/kg (1.51–2.55 mg/kg), respectively. Aspartate aminotransferase and alanine aminotransferase were elevated post-embolization but resolved within 2 weeks. One rabbit died two days after TACE with pyloric duodenal perforation observed at necropsy, potentially due to non-target embolization. In vitro elution of topotecan from ROMTOP was complete in 10 h compared to 3 h for irinotecan-loaded microspheres. Selective embolization with ROMTOP was tolerated at a dose of 2 mg/kg (24 mg/m2) in rabbits. In vitro topotecan elution from microspheres was more prolonged compared to irinotecan.

To evaluate the loading and elution of topotecan from radiopaque microspheres (ROMTOP) and determine the maximum dose that could be safely administered by transarterial chemoembolization in a rabbit preclinical model. All animal procedures were approved by the Animal Care and Use Committee. Topotecan elution from radiopaque microspheres (70-150 μm) was assessed in vitro using an open-loop flow-through system and compared to irinotecan. Rabbits underwent hepatic transarterial chemoembolization with topotecan-loaded radiopaque microspheres under fluoroscopic guidance until angiographic stasis. A 3+3 dose escalation study design was adopted to determine the maximum tolerated dose (MTD). Physical examination and behavioral assessment for adverse events were performed daily and liver function tests and complete blood counts were performed at regular intervals until euthanasia 28 days post chemoembolization. The maximum topotecan loading capacity in ROMTOP was 80 mg/mL. Complete drug elution of topotecan and irinotecan from microspheres took 10 and 3 hours in vitro, respectively, providing a direct comparison of topotecan to the better-characterized irinotecan. All rabbits survived for 28 days in the bland bead (dose: 0 mg/kg, N = 3) and low-dose (mean dose, 0.54 mg/kg, N = 3) cohorts. In the high-dose cohort (mean dose, 1.99 mg/kg, N = 6), one of six rabbits treated died two days after chemoembolization from pyloric duodenal perforation. All other rabbits survived for 28 days without dose limiting toxicity. An additional 5 rabbits were excluded from the study due to technical / procedural complications. No further dose escalation was possible as the maximum topotecan loading in the microspheres had been reached. Toxicity related to liver embolization with ROMTOP included alanine aminotransferase and aspartate transaminase elevations lasting 7-14 days. Embolization with ROMTOP was well tolerated up to a dose of 2 mg/kg, the maximum loading capacity of the microspheres. Topotecan may be an attractive candidate for local delivery via TACE with radiopaque drug-eluting microspheres due to its high potency and sustained drug release kinetics relative to irinotecan.

The in vitro and in vivo handling and performance characteristics of a small caliber radiopaque embolic microsphere, 40-90 mu m DC Bead LUMI (TM) (LUMI40-90), were studied. Microsphere drug loading and elution and effects on size, suspension, and microcatheter delivery were evaluated using established in vitro methodologies. In vivo evaluations of vascular penetration (rabbit renal artery embolization), long-term biocompatibility and X-ray imaging properties, pharmacokinetics and local tissue effects of both doxorubicin (Dox) and irinotecan (Iri) loaded microspheres (swine hepatic artery embolization) were conducted. Compared to 70-150 mu m DC Bead LUMI (LUMI70-150), LUMI40-90 averaged 70 mu m versus 100 mu m, which was unchanged upon drug loading. Handling, suspension, and microsphere delivery studies were successfully performed. Dox loading was faster (20 min) and Iri equivalent (<10 min) while drug elution rates were similar. Contrast suspension times were longer with no delivery complications. Vascular penetration was statistically greater (rabbit) with no unexpected adverse safety findings (swine). Microspheres +/- drug were visible under X-ray imaging (CT) at 90 days. Peak plasma drug levels and area under the curve were greater for LUMI40-90 compared to LUMI70-150 but comparable to 70-150 mu m DC BeadM1 (TM) (DC70-150). Local tissue effects showed extensive hepatic necrosis for Dox, whereas Iri displayed lower toxicity with more pronounced lobar fibrosis. LUMI40-90 remains suspended for longer and have greater vessel penetration compared to the other DC Bead LUMI sizes and are similarly highly biocompatible with long-term visibility under X-ray imaging. Drug loading is equivalent or faster with pharmacokinetics similar to DC70-150 for both Dox and Iri.

There are currently two methods widely used in clinical practice to perform transarterial chemoembolization (TACE). One is based on mixing an aqueous drug with an iodized oil (Lipiodol) and creating an emulsion that is delivered intraarterially, followed by embolization with a particulate agent. The other is based on a one-step TACE using Drug-eluting Beads (DEBs) loaded with drug. It is not recommended to mix Lipiodol with DEBs due to incompatibility. For the first time, novel DEB: Lipiodol: doxorubicin (Dox) emulsions are identified using lyophilized polyvinyl alcohol (PVA) hydrogels (non-iodinated or iodinated) DEBs. Methods: 15 DEB emulsions (50mg Dox) were assessed for stability and deliverability in vitro and in vivo in a swine model. Dox release from selected formulations was measured in vitro using a vascular flow model and in vivo in a VX2 rabbit tumor model. Results: Both DEB formats were shown to be able to form emulsions, however only Iodinated DEBs consistently met defined handling criteria. Those based on the non-iodinated DEB achieved >99%+ Dox loading in <5 minutes but were generally less stable. Those prepared using iodinated DEBs, which are more hydrophobic, were able to form stable Pickering-like emulsions (separation time >= 20 minutes) and demonstrated handling, administration and imaging observations more akin to Lipiodol (TM) TACE emulsions in both embolization models. Controlled Dox release and hence beneficial in vivo pharmacokinetics associated with DEB-TACE were maintained. Conclusions: This study demonstrates that it is possible to formulate novel DEB emulsions suitable for TACE that combine positive elements of both Lipiodol (TM) based and DEB-TACE procedures.

The purpose of this study was to evaluate LC Bead LUMI™ (40–90 µm and 70–150 µm) in order to determine if their increased resistance to compression influences microsphere penetration and distribution compared to more compressible commercial microspheres. LC Bead LUMI™ 40–90 µm and 70–150 µm, LC BeadM1® 70–150 µm, Embozene™ 40 µm and Embozene™ 100 µm size and distributions were measured using optical microscopy. Penetration in vitro was evaluated using an established ‘plate model’, consisting of a calibrated tapered gap between a glass plate and plastic housing to allow visual observation of microsphere penetration depth. Behaviour in vivo was assessed using a rabbit renal embolization model with histopathologic confirmation of vessel penetration depth. Penetration behaviour in vitro was reproducible and commensurate with the measured microsphere size, the smaller the microsphere the deeper the penetration. Comparison of the microsphere diameter measured on the 2D plate model versus the corresponding average microsphere size measured by histopathology in the kidney showed no significant differences (p = > 0.05 Mann-Whitney, demonstrating good in vitro - in vivo predictive capabilities of the plate model) confirming predictable performance for LC Bead LUMI™ (40–90 µm and 70–150 µm) based on microsphere size, their increased rigidity having no bearing on their depth of penetration and distribution. An assessment of a LC Bead LUMI™ (40–90 µm and 70–150 µm) has shown that despite having greater resistance to compression, these microspheres behave in a predictable manner within in vitro and in vivo models comparable with more compressible microspheres of similar sizes.

This review describes the historical development of an imageable spherical embolic agent and focuses on work performed in collaboration between Biocompatibles UK Ltd (a BTG International group company) and the NIH to demonstrate radiopaque bead utility and bring a commercial offering to market that meets a clinical need. Various chemistries have been investigated and multiple prototypes evaluated in search of an optimized product with the right balance of handling and imaging properties. Herein, we describe the steps taken in the development of DC Bead LUMI™, the first commercially available radiopaque drug-eluting bead, ultimately leading to the first human experience of this novel embolic agent in the treatment of liver tumors.

Purpose To correlate bead location and attenuation on CT images with the quantity and distribution of drug delivered to the liver following transarterial chemoembolization (TACE) with radiopaque drug-eluting beads (DEB) in a rabbit tumor model. Materials and Methods All procedures were performed with a protocol approved by the Institutional Animal Care and Use Committee. TACE was performed in rabbits (n = 4) bearing VX2 liver tumors by using radiopaque DEB (70-150 µm) loaded with doxorubicin (DOX). Livers were resected 1 hour after embolization, immediately frozen, and cut by using liver-specific three-dimensional-printed molds for colocalization of liver specimens and CT imaging. DOX penetration into tissue surrounding beads was evaluated with fluorescence microscopy. DOX levels in liver specimens were predicted by using statistical models correlating DOX content measured in tissue with bead volume and attenuation measured on CT images. Model predictions were then compared with actual measured DOX concentrations to assess the models' predictive power. Results Eluted DOX remained in close proximity (<600 µm) to beads in the liver 1 hour after TACE. Bead volume and attenuation measured on CT images demonstrated positive linear correlations (0.950 and 0.965, respectively) with DOX content in liver specimens. DOX content model predictions based on CT images were accurate compared with actual liver DOX levels at 1 hour. Conclusion CT may be used to estimate drug dose delivery and distribution in the liver following transarterial chemoembolization (TACE) with doxorubicin-loaded radiopaque drug-eluting beads (DEB). Although speculative, this informational map might be helpful in planning and understanding the spatial effects of TACE with DEB. © RSNA, 2018.

We have developed a straightforward and efficient method of introducing radiopacity into Polyvinyl alcohol (PVA)-2-Acrylamido-2-methylpropane sulfonic acid (AMPS) hydrogel beads (DC Bead™) that are currently used in the clinic to treat liver malignancies. Coupling of 2,3,5-triiodobenzaldehyde to the PVA backbone of pre-formed beads yields a uniformly distributed level of iodine attached throughout the bead structure (~150mg/mL) which is sufficient to be imaged under standard fluoroscopy and computed tomography (CT) imaging modalities used in treatment procedures (DC Bead LUMI™). Despite the chemical modification increasing the density of the beads to ~1.3g/cm3 and the compressive modulus by two orders of magnitude, they remain easily suspended, handled and administered through standard microcatheters. As the core chemistry of DC Bead LUMI™ is the same as DC Bead™, it interacts with drugs using ion-exchange between sulfonic acid groups on the polymer and the positively charged amine groups of the drugs. Both doxorubicin (Dox) and irinotecan (Iri) elution kinetics for all bead sizes evaluated were within the parameters already investigated within the clinic for DC Bead™. Drug loading did not affect the radiopacity and there was a direct relationship between bead attenuation and Dox concentration. The ability (Dox)-loaded DC Bead LUMI™ to be visualized in vivo was demonstrated by the administration of into hepatic arteries of a VX2 tumor-bearing rabbit under fluoroscopy, followed by subsequent CT imaging.

To compare bead visualization in vivo with cone-beam CT (CBCT) that is not optimized for radiopaque bead visualization to ex vivo microCT imaging to better inform and map true bead distribution. Swine (n = 2) underwent hepatic TACE (n = 3) using radiopaque embolic beads (70-150 µm, LC Bead LUMI) until flow stasis under fluoroscopic guidance. After embolization, in vivo CBCT at 120 kVp was performed using an Allura Xper FD20 x‐ray system (Philips, Andover, MA) with image resolution of 0.656 mm. After the procedure, the liver was resected and the embolized regions were identified under fluoroscopy and isolated. The embolized liver specimens were imaged using a Bruker SkyScan 1176 in-vivo Micro-CT with image resolution of 17.49 µm. The resulting images were segmented using a constant threshold value and registered using point registration (Mimics 19.0, Materialise, Leuven, Belgium). The volume, surface area, and length of the vessel centerlines were calculated for each segmentation. CBCT values were expressed as a percentage of microCT. Distribution of the radiopaque beads was defined on microCT and unoptimized CBCT. The visualized embolization volume and surface area using unoptimized CBCT was significantly less than that observed under microCT, 37 ± 1% (p<0.0003) and 10.3 ± 0.2% (p<0.000007) respectively. The length of the vessel centerlines on CBCT was less than on microCT, 2.6 ± 0.5% (p<0.00003). Individual beads were apparent on microCT. Standard unoptimized CBCT at 120kVp and microCT allowed for visualization of LC Bead LUMI within the hepatic vasculature after TACE. Unoptimized CBCT underestimates both the volume and distribution of radiopaque beads in hepatic tissue compared to microCT. Intra-procedural and post-procedural imaging modalities (fluoroscopy, CBCT and CT) may underestimate true embolization volume and distribution. Clinicians should be aware of the differences between clinical imaging results and the true delivery and distribution of radiopaque beads during embolization. Future work will seek to define the added conspicuity of optimized CBCT customized for LC Bead LUMI.

The objective of this study was to undertake a comprehensive long-term biocompatibility and imaging assessment of a new intrinsically radiopaque bead (LC Bead LUMI™) for use in transarterial embolization. The sterilized device and its extracts were subjected to the raft of ISO10993 biocompatibility tests that demonstrated safety with respect to cytotoxicity, mutagenicity, blood contact, irritation, sensitization, systemic toxicity and tissue reaction. Intra-arterial administration was performed in a swine model of hepatic arterial embolization in which 0.22-1 mL of sedimented bead volume was administered to the targeted lobe(s) of the liver. The beads could be visualized during the embolization procedure with fluoroscopy, DSA and single X-ray snapshot imaging modalities. CT imaging was performed before and 1 h after embolization and then again at 7, 14, 30 and 90 days. LC Bead LUMI™ could be clearly visualized in the hepatic arteries with or without administration of IV contrast and appeared more dense than soluble contrast agent. The CT density of the beads did not deteriorate during the 90 day evaluation period. The beads embolized predictably and effectively, resulting in areas devoid of contrast enhancement on CT imaging suggesting ischaemia-induced necrosis nearby the sites of occlusion. Instances of off target embolization were easily detected on imaging and confirmed pathologically. Histopathology revealed a classic foreign body response at 14 days, which resolved over time leading to fibrosis and eventual integration of the beads into the tissue, demonstrating excellent long-term tissue compatibility.

Purpose: To develop a simple method to produce radiopaque drug-eluting microspheres (drug-eluting beads [DEBs]) that could be incorporated into the current clinical transcatheter arterial chemoembolization workflow and evaluate their performance in vitro and in vivo.Materials and Methods: An ethiodized oil (Lipiodol; Guerbet, Villepinte, France) and ethanol solution was added to a lyophilized 100-300 mu m bead before loading with doxorubicin. These radiopaque drug-eluting beads (DEBs; Biocompatibles UK Ltd, Farnham, United Kingdom) were evaluated in vitro for x-ray attenuation, composition, size, drug loading and elution, and correlation between attenuation and doxorubicin concentration. In vivo conspicuity was evaluated in a VX2 tumor model.Results: Lipiodol was loaded into lyophilized beads using two glass syringes and a three-way stopcock. Maximum bead attenuation was achieved within 30 minutes. X-ray attenuation of radiopaque beads increased linearly (21-867 HU)with the amount of beads (0.4-12.5 vol%; R-2 = 0.9989). Doxorubicin loading efficiency and total amount eluted were similar to DC Bead (Biocompatibles UK Ltd); however, the elution rate was slower for radiopaque DEBs (P < 05). Doxorubicin concentration linearly correlated with x-ray attenuation of radiopaque DEBs: (R-2 = 0.99). Radiopaque DEBs were seen in tumor feeding arteries after administration by fluoroscopy, computed tomography, and micro-computed tomography, and their location was confirmed by histology.Conclusions: A simple, rapid method to produce radiopaque DEBs was developed. These radiopaque DEBs provided sufficient conspicuity to be visualized with x-ray imaging techniques.

PURPOSE:Embolotherapy using microshperes is currently performed with soluble contrast to aid in visualization. However, administered payload visibility dimishes soon after delivery due to soluble contrast washout, leaving the radiolucent bead's location unknown. The objective of our study was to characterize inherently radiopaque beads (RO Beads) in terms of physicomechanical properties, deliverability and imaging visibility in a rabbit VX2 liver tumor model.MATERIALS AND METHODS:RO Beads, which are based on LC Bead® platform, were compared to LC Bead. Bead size (light microscopy), equilibrium water content (EWC), density, X-ray attenuation and iodine distribution (micro-CT), suspension (settling times), deliverability and in vitro penetration were investigated. Fifteen rabbits were embolized with either LC Bead or RO Beads + soluble contrast (iodixanol-320), or RO Beads+dextrose. Appearance was evaluated with fluoroscopy, X-ray single shot, cone-beam CT (CBCT).RESULTS:Both bead types had a similar size distribution. RO Beads had lower EWC (60-72%) and higher density (1.21-1.36 g/cc) with a homogeneous iodine distribution within the bead's interior. RO Beads suspension time was shorter than LC Bead, with durable suspension (>5 min) in 100% iodixanol. RO Beads ≤300 µm were deliverable through a 2.3-Fr microcatheter. Both bead types showed similar penetration. Soluble contrast could identify target and non-target embolization on fluoroscopy during administration. However, the imaging appearance vanished quickly for LC Bead as contrast washed-out. RO Beads+contrast significantly increased visibility on X-ray single shot compared to LC Bead+contrast in target and non-target arteries (P=0.0043). Similarly, RO beads demonstrated better visibility on CBCT in target arteries (P=0.0238) with a trend in non-target arteries (P=0.0519). RO Beads+dextrose were not sufficiently visible to monitor embolization using fluoroscopy.CONCLUSION:RO Beads provide better conspicuity to determine target and non-target embolization compared to LC Bead which may improve intra-procedural monitoring and post-procedural evaluation of transarterial embolization.

To describe first clinical experience with a directly image-able, inherently radio-opaque microspherical embolic agent for transarterial embolization of liver tumors.

To relate DEROB-associated attenuation with amount of drug delivered in liver tissue post-DEBTACE with a novel radiopaque embolic microsphere in a preclinical model. The x-ray attenuation of radiopaque beads containing known amounts of doxorubicin was correlated with different bead volumes in a phantom using a 16-slice multidetector CT scanner (MDCT). Rabbits bearing implanted VX2 hepatic tumors underwent TACE to flow stasis from the proper hepatic artery with DEROB under fluoroscopic / CBCT guidance. Postprocedural imaging was performed using an Allura Xper FD20 CBCT x-ray system and/or MDCT scanner. Livers were resected 1h post TACE and dissected into multiple sections containing varying (arbitrary) bead volumes for analysis of bead attenuation. The CT attenuation corresponding to different bead volumes in liver sections was determined by image segmentation and volume rendering and compared to in vitro data libraries to estimate drug dose delivered. Analysis of ex vivo liver samples demonstrated high attenuation associated with beads allowing for determination of bead volume. A linear correlation between the bead volume and attenuation of radiopaque beads was observed in vitro and in ex vivo sections (R2 = 0.997 and R2 = 0.911, respectively). Challenges exist regarding differentiation of bead from static vascular contrast, but drug dose delivered to the liver based on bead-associated attenuation in CT images provides a relative estimate of spatial drug distribution. A linear relationship between DEROB volume and attenuation was observed in vitro and in rabbit livers following TACE. This relationship provides an important relative variable in the estimation of drug dose delivered according to measured post-embolization bead-related attenuation. Although speculative, such relative dose maps may contribute to identification and treatment of tissue at risk for under-dosage, which could improve TACE outcomes.

Embolization procedures to treat liver tumors are currently performed with soluble contrast to aid in visualization, however the bead location is unknown and often inferred from contrast retention. The purpose of this study was to characterize the performance of inherently radio-opaque beads (ROBs) in terms of deliverability and imaging visibility in a rabbit VX2 tumor model. The ROBs are based on LC Bead® (Biocompatibles UK Ltd) and are supplied as hydrated and ready to use (nothing to add). Size was characterized by light microscopy, X-ray attenuation and iodine distribution measured by microCT, suspension evaluated by measuring settling time in a 3cc syringe, and penetration estimated by in-vitro assay. 20 rabbits with VX2 liver tumors were embolized with either 1) ROB + D50W, 2) ROB + contrast (Iodixanol) or 3) LC Bead + contrast. Imaging appearance was evaluated with fluoroscopy, single snapshot, CBCT and MDCT. ROBs have similar size distribution to LC Bead®. Interior iodine concentration within the ROB was homogeneous. ROB suspension time in contrast was shorter than LC Bead® of the same size. A durable suspension (>5min) was obtained with 70-150μm ROB in 100% Iodixanol but shorter suspension times were obtained with diluted contrast medium, larger bead sizes or other contrast. ROBs showed the same penetration as LC Bead® in an in-vitro assay. ROBs in D50W were faintly visible in transit on real-time fluoroscopy, but highly visible and persisted on single snapshot once deposited in the hepatic and non-target arteries. CBCT clearly depicted their distribution in target and nontarget arteries even in absence of contrast. When ROBs and LC Bead® were delivered with contrast, dynamic reflux was easily observed on fluoroscopy. However, with ROBs it was not possible to determine if the immediate conspicuity was due to contrast or ROBs themselves. The added value of ROBs over LC Bead® after delivery in contrast was demonstrated by improved conspicuity on all imaging techniques when forward blood flow remained allowing for soluble contrast washout, even after 7 days. ROBs may provide better conspicuity to determine target and nontarget embolization following delivery.

A novel analysis system for the quantification of sclerosing foam properties under clinically relevant conditions was developed with the purpose of establishing a robust methodology for comparative characterisation of different foam formulations and production strategies. The developed biomimetic-inspired model comprised of 4 or 10 mm inner diameter polytetrafluoroethylene tubing, filled with a blood substitute and fixed to a platform with an adjustable inclination angle. Sclerosing foams were produced by mixing polidocanol with either atmospheric air or 100 % CO2, using a double-syringe system method. Individual foams were injected into the tube, while videos were captured simultaneously. Videos were then transferred to an in-house computational foam analysis system (CFAS) which performed a sequence of semi-automated operations, allowing quantitative characterisation of sclerosing foam dynamic behaviour. Using CFAS, degradation rates of different foams were measured and the effect of gas composition, liquid sclerosant concentration and time delay between foam production and injection were evaluated.