Characterization of a novel liquid fiducial marker for multimodal image guidance in stereotactic body radiotherapy of prostate cancer

Indocyanine green and iohexol loaded hydroxyapatite in poly(L-lactide-co-caprolactone)-based composite for bimodal near-infrared fluorescence- and X-ray-based imaging

This study aimed to develop material for multimodal imaging by means of X-ray and near-infrared containing FDA- and EMA-approved iohexol and indocyanine green (ICG). The mentioned contrast agents (CAs) are hydrophilic and amphiphilic, respectively, which creates difficulties in fabrication of functional polymeric composites for fiducial markers (FMs) with usage thereof. Therefore, this study exploited for the first time the possibility of enhancing the radiopacity and introduction of the NIR fluorescence of FMs by adsorption of the CAs on hydroxyapatite (HAp) nanoparticles. The particles were embedded in the poly(L-lactide-co-caprolactone) (P[LAcoCL]) matrix resulting in the composite material for bimodal near-infrared fluorescence- and X-ray-based imaging. The applied method of material preparation provided homogenous distribution of both CAs with high iohexol loading efficiency and improved fluorescence signal due to hindered ICG aggregation. The material possessed profound contrasting properties for both imaging modalities. Its stability was evaluated during in vitro experiments in phosphate-buffered saline (PBS) and foetal bovine serum (FBS) solutions. The addition of HAp nanoparticles had significant effect on the fluorescence signal. The X-ray radiopacity was stable within minimum 11 weeks, even though the addition of ICG contributed to a faster release of iohexol. The stiffness of the material was not affected by iohexol or ICG, but incorporation of HAp nanoparticles elevated the values of bending modulus by approximately 70%. Moreover, the performed cell study revealed that all tested materials were not cytotoxic. Thus, the developed material can be successfully used for fabrication of FMs.

Feasibility and guidelines for the use of an injectable fiducial marker (BioXmark ®) to improve target delineation in preclinical radiotherapy studies using mouse models

BACKGROUND

Preclinical models of radiotherapy (RT) response are vital for the continued success and evolution of RT in the treatment of cancer. The irradiation of tissues in mouse models necessitates high levels of precision and accuracy to recapitulate clinical exposures and limit adverse effects on animal welfare. This requirement has been met by technological advances in preclinical RT platforms established over the past decade. Small animal RT systems use onboard computed tomography (CT) imaging to delineate target volumes and have significantly refined radiobiology experiments with major 3Rs impacts. However, the CT imaging is limited by the differential attenuation of tissues resulting in poor contrast in soft tissues. Clinically, radio-opaque fiducial markers (FMs) are used to establish anatomical reference points during treatment planning to ensure accuracy beam targeting, this approach is yet to translate back preclinical models.

METHODS

We report on the use of a novel liquid FM BioXmark ® developed by Nanovi A/S (Kongens Lyngby, Denmark) that can be used to improve the visualisation of soft tissue targets during beam targeting and minimise dose to surrounding organs at risk. We present descriptive protocols and methods for the use of BioXmark ® in experimental male and female C57BL/6J mouse models.

RESULTS

These guidelines outline the optimum needle size for uptake (18-gauge) and injection (25- or 26-gauge) of BioXmark ® for use in mouse models along with recommended injection volumes (10-20 µl) for visualisation on preclinical cone beam CT (CBCT) scans. Injection techniques include subcutaneous, intraperitoneal, intra-tumoral and prostate injections.

CONCLUSIONS

The use of BioXmark ® can help to standardise targeting methods, improve alignment in preclinical image-guided RT and significantly improve the welfare of experimental animals with the reduction of normal tissue exposure to RT.

A liquid immunogenic fiducial eluter for image-guided radiotherapy

Introduction

Fiducials are routinely used to provide image-guidance during radiotherapy. Here, a new nanoparticle-based liquid immunogenic fiducial is investigated for its potential to provide image-guidance, while also enhancing treatment outcomes.

Methods

This fiducial, liquid immunogenic fiducial eluter (LIFE) biomaterial, is formulated with natural biodegradable polymers, chitosan and sodium alginate with radio-sensitizing nanoparticles, and immunoadjuvant like anti-CD40 monoclonal antibody. Once administered intra-tumorally, this liquid smart radiotherapy biomaterial congeals within the calcium rich tumor microenvironment. The potential use of LIFE biomaterial for providing image guidance in magnetic resonance imaging (MRI) and computed tomography (CT) was investigated over different time period in a pre-clinical tumored mouse model.

Results

Results showed that the LIFE biomaterial can provide both MRI contrast and CT imaging contrast over 3-weeks, with gradual decrease of the contrast over time, as the LIFE biomaterial biodegrades. Results also showed the LIFE biomaterial significantly slowed tumor growth and prolonged mice survival (p < 0.0001) over time.

Discussion

The results highlight the potential use of the LIFE biomaterial as a multi-functional smart radiotherapy biomaterial that could be developed and optimized for hypo-fractionated radiotherapy applications and combining radiotherapy with immunoadjuvants.

Long-Term In Vitro Assessment of Biodegradable Radiopaque Composites for Fiducial Marker Fabrication

Biodegradable polymer-based composite materials may be successfully utilised to fabricate fiducial markers (FMs), which are intended to precisely label tumour margins during image-guided surgery or radiotherapy. However, due to matrix degradability, the stability of the functional properties of FMs depends on the chosen polymer. Thus, this study aimed to investigate novel radiopaque composites which varied in the polymeric matrix-polycaprolactone (PCL), poly(L-lactide-co-caprolactone) (P[LAcoCL]) with two molar ratios (70:30 and 85:15), and poly(L-lactide-co-glycolide) (with molar ratio 82:18). The radiopaque component of the materials was a mixture of barium sulphate and hydroxyapatite. The changes in water contact angle, stiffness, and radiopacity occurring during the 24-week-long degradation experiment were examined for the first time. This study comprehensively analyses the microstructural causes of composites behaviour within degradation experiments using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), gel permitted chromatography (GPC), and scanning electron microscopy (SEM). The obtained results suggest that the utilized biodegradable matrix plays an essential role in radiopaque composite properties and stability thereof. This long-term in vitro assessment enabled a comparison of the materials and aided in choosing the most favourable composite for FMs' fabrication.

BioXmark® liquid fiducials to enable radiotherapy tumor boosting in rectal cancer, a feasibility trial

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BioXmark® is a novel liquid fiducial marker for image-guided radiotherapy.

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The marker remained stable during chemoradiotherapy in 96% of rectal cancer cases.

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The fiducial allows for image tracking on CT-based imaging modalities.

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Marker visibility was good using CT-based imaging without any relevant artifacts.

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The marker is easy to inject without marker related adverse events.

Background and purpose

Dose-escalation in rectal cancer (RCa) may result in an increased complete response rate and thereby enable omission of surgery and organ preservation. In order to implement dose-escalation, it is crucial to develop a technique that allows for accurate image-guided radiotherapy. The aim of the current study was to determine the performance of a novel liquid fiducial marker (BioXmark®) in RCa patients during the radiotherapy course by assessing its positional stability on daily cone-beam CT (CBCT), technical feasibility, visibility on different imaging modalities and safety.

Materials and methods

Prospective, non-randomized, single-arm feasibility trial with inclusion of twenty patients referred for neoadjuvant chemoradiotherapy for locally advanced RCa. Primary study endpoint was positional stability on CBCT. Furthermore, technical aspects, safety and clinical performance of the marker, such as visibility on different imaging modalities, were evaluated.

Results

Seventy-four markers from twenty patients were available for analysis. The marker was stable in 96% of the cases. One marker showed clinically relevant migration, one marker was lost before start of treatment and one marker was lost during treatment. Marker visibility was good on computed tomography (CT) and CBCT, and moderate on electronic portal imaging (EPI). Marker visibility on magnetic resonance imaging (MRI) was poor during response evaluation.

Conclusion

The novel liquid fiducial marker demonstrated positional stability. We provide evidence of the feasibility of the novel fiducial marker for image-guided radiotherapy on daily cone beam CT for RCa patients.

Biodegradable Fiducial Markers for Bimodal Near-Infrared Fluorescence- and X-ray-Based Imaging

This study aimed to evaluate, for the first time, implantable, biodegradable fiducial markers (FMs), which were designed for bimodal, near-infrared fluorescence-based (NIRF) and X-ray-based imaging. The developed FMs had poly(l-lactide-co-caprolactone)-based core-shell structures made of radiopaque (core) and fluorescent (shell) composites with a poly(l-lactide-co-caprolactone) matrix. The approved for human use contrast agents were utilized as fillers. Indocyanine green was applied to the shell material, whereas in the core materials, iohexol and barium sulfate were compared. Moreover, the possibility of tailoring the stability of the properties of the core materials by the addition of hydroxyapatite (HAp) was examined. The performed in situ (porcine tissue) and in vivo experiment (rat model) confirmed that the developed FMs possessed pronounced contrasting properties in NIRF and X-ray imaging. The presence of HAp improved the radiopacity of FMs at the initial state. It was also proved that, in iohexol-containing FMs, the presence of HAp slightly decreased the stability of contrasting properties, while in BaSO₄-containing ones, changes were less pronounced. A comprehensive material analysis explaining the differences in the stability of the contrasting properties was also presented. The tissue response around the FMs with composite cores was comparable to that of the FMs with a pristine polymeric core. The developed composite FMs did not cause serious adverse effects on the surrounding tissues even when irradiated in vivo. The developed FMs ensured good visibility for NIRF image-supported tumor surgery and the following X-ray image-guided radiotherapy. Moreover, this study replenishes a scanty report regarding similar biodegradable composite materials with a high potential for application.

Evaluation of computed tomography settings in the context of visualization and discrimination of low dose injections of a novel liquid soft tissue fiducial marker in head and neck imaging

Background

Intraoperative incorporation of radiopaque fiducial markers at the tumor resection surface can provide useful assistance in identifying the tumor bed in postoperative imaging for RT planning and radiological follow-up. Besides titanium clips, iodine containing injectable liquid fiducial markers represent an option that has emerged more recently for this purpose. In this study, marking oral soft tissue resection surfaces, applying low dose injections of a novel Conformité Européenne (CE)-marked liquid fiducial marker based on sucrose acetoisobutyrate (SAIB) and iodinated SAIB (x-SAIB) was investigated.

Methods

Visibility and discriminability of low dose injections of SAIB/x-SAIB (10 µl, 20 µl, 30 µl) were systematically studied at different kV settings used in clinical routine in an ex-vivo porcine mandible model. Transferability of the preclinical results into the clinical setting and applicability of DE-CT were investigated in initial patients.

Results

Markers created by injection volumes as low as 10 µl were visible in CT imaging at all kV settings applied in clinical routine (70–120 kV). An injection volume of 30 µl allowed differentiation from an injection volume of 10 µl. In a total of 118 injections performed in two head and neck cancer patients, markers were clearly visible in 83% and 86% of injections. DE-CT allowed for differentiation between SAIB/x-SAIB markers and other hyperdense structures.

Conclusions

Injection of low doses of SAIB/x-SAIB was found to be a feasible approach to mark oral soft tissue resection surfaces, with injection volumes as low as 10 µl found to be visible at all kV settings applied in clinical routine. With the application of SAIB/x-SAIB reported for tumors of different organs already, mostly applying relatively large volumes for IGRT, this study adds information on the applicability of low dose injections to facilitate identification of the tumor bed in postoperative CT and on performance of the marker at different kV settings used in clinical routine.

Novel artifact-robust and highly visible zinc solid fiducial marker for kilovoltage x-ray image-guided radiation therapy

PURPOSE

To develop a novel biocompatible solid fiducial marker that prevents radiopaque imaging artifacts and also maintains high imaging contrast for kilovoltage x-ray image-guided radiation therapy.

METHODS

The fiducial marker was made of pure zinc. An in-house water-equivalent phantom was designed to evaluate artifacts and visibility under various simulated treatment scenarios. Image artifacts were quantitatively assessed in terms of the metal artifact index (MAI) on kilovoltage computed tomography (CT) and cone-beam CT (CBCT) scans. Marker visibility was evaluated on two types of kilovoltage planar x-ray images in terms of the contrast-to-background ratio (CBR). Comparisons with a conventional gold fiducial marker were conducted.

RESULTS

The use of zinc rather than a gold marker mitigates imaging artifacts. The MAI near the zinc marker decreased by 76, 79, and 77 % in CT, and by 77 (81), 74 (80), and 79 (85) % in CBCT full-fan (half-fan) scans, when using one-, two-, and three-marker phantom settings, respectively. The high-contrast part of the zinc marker exhibited CBRs above 2.00 for 28/32 exposures under four (lung, tissue, low-density bone, and high-density bone) different simulation scenarios, making its visibility comparable to that of the gold marker (30/32 exposures with CBRs > 2.00).

CONCLUSIONS

We developed a biocompatible, artifact-robust, and highly visible solid zinc fiducial marker. Although further evaluation is needed in clinical settings, our findings suggest its feasibility and benefits for kilovoltage x-ray image-guided radiation therapy.

Evaluation of a Novel Liquid Fiducial Marker, BioXmark®, for Small Animal Image-Guided Radiotherapy Applications

BioXmark^® (Nanovi A/S, Denmark) is a novel fiducial marker based on a liquid, iodine-based and non-metallic formulation. BioXmark^® has been clinically validated and reverse translated to preclinical models to improve cone-beam CT (CBCT) target delineation in small animal image-guided radiotherapy (SAIGRT). However, in phantom image analysis and in vivo evaluation of radiobiological response after the injection of BioXmark^® are yet to be reported. In phantom measurements were performed to compare CBCT imaging artefacts with solid fiducials and determine optimum imaging parameters for BioXmark^®. In vivo stability of BioXmark^® was assessed over a 5-month period, and the impact of BioXmark^® on in vivo tumour response from single-fraction and fractionated X-ray exposures was investigated in a subcutaneous syngeneic tumour model. BioXmark^® was stable, well tolerated and detectable on CBCT at volumes ≤10 µL. Our data showed imaging artefacts reduced by up to 84% and 89% compared to polymer and gold fiducial markers, respectively. BioXmark^® was shown to have no significant impact on tumour growth in control animals, but changes were observed in irradiated animals injected with BioXmark^® due to alterations in dose calculations induced by the sharp contrast enhancement. BioXmark^® is superior to solid fiducials with reduced imaging artefacts on CBCT. With minimal impact on the tumour growth delay, BioXmark^® can be implemented in SAIGRT to improve target delineation and reduce set-up errors.

Stereotactic body radiation therapy with optional focal lesion ablative microboost in prostate cancer: Topical review and multicenter consensus

Stereotactic body radiotherapy (SBRT) for prostate cancer (PCa) is gaining interest by the recent publication of the first phase III trials on prostate SBRT and the promising results of many other phase II trials. Before long term results became available, the major concern for implementing SBRT in PCa in daily clinical practice was the potential risk of late genitourinary (GU) and gastrointestinal (GI) toxicity. A number of recently published trials, including late outcome and toxicity data, contributed to the growing evidence for implementation of SBRT for PCa in daily clinical practice. However, there exists substantial variability in delivering SBRT for PCa. The aim of this topical review is to present a number of prospective trials and retrospective analyses of SBRT in the treatment of PCa. We focus on the treatment strategies and techniques used in these trials. In addition, recent literature on a simultaneous integrated boost to the tumor lesion, which could create an additional value in the SBRT treatment of PCa, was described. Furthermore, we discuss the multicenter consensus of the FLAME consortium on SBRT for PCa with a focal boost to the macroscopic intraprostatic tumor nodule(s).

Detectability and structural stability of a liquid fiducial marker in fresh ex vivo pancreas tumour resection specimens on CT and 3T MRI

PURPOSE

To test the detectability of a liquid fiducial marker injected into ex vivo pancreas tumour tissue on magnetic resonance imaging (MRI) and computed tomography (CT). Furthermore, its injection performance using different needle sizes and its structural stability after fixation in formaldehyde were investigated.

METHODS

Liquid fiducial markers with a volume of 20-100 µl were injected into freshly resected pancreas specimens of three patients with suspected adenocarcinoma. X‑ray guided injection was performed using different needle sizes (18 G, 22 G, 25 G). The specimens were scanned on MRI and CT with clinical protocols. The markers were segmented on CT by signal thresholding. Marker detectability in MRI was assessed in the registered segmentations. Marker volume on CT was compared to the injected volume as a measure of backflow.

RESULTS

Markers with a volume ≥20 µl were detected as hyperintensity on X‑ray and CT. On T₁- and T₂-weighted 3T MRI, marker sizes ranging from 20-100 µl were visible as hypointensity. Since most markers were non-spherical, MRI detectability was poor and their differentiation from hypointensities caused by air cavities or surgical clips was only feasible with a reference CT. Marker backflow was only observed when using an 18-G needle. A volume decrease of 6.6 ± 13.0% was observed after 24 h in formaldehyde and, with the exception of one instance, no wash-out occurred.

CONCLUSIONS

The liquid fiducial marker injected in ex vivo pancreatic resection specimen was visible as hyperintensity on kV X‑ray and CT and as hypointensity on MRI. The marker's size was stable in formaldehyde. A marker volume of ≥50 µL is recommended in clinically used MRI sequences. In vivo injection is expected to improve the markers sphericity due to persisting metabolism and thereby enhance detectability on MRI.

Visualization of the tumor cavity after lumpectomy of breast cancer for postoperative radiotherapy

To visualize the tumor cavity after lumpectomy, the tumor cavity was coated with the liquid tissue marker sucrose acetate isobutyrate (SAIB) with its radiopaque electron dense SAIB analogue (x-SAIB) and assessed for radiotherapy planning. SAIB/x-SAIB enhanced the confidence for target structure definition. Tissue displacement after oncoplasty may be revealed by SAIB/x-SAIB.

Evaluation of gold fiducial marker manual localisation for magnetic resonance-only prostate radiotherapy

BACKGROUND

The use of intraprostatic gold fiducial markers (FMs) ensures highly accurate and precise image-guided radiation therapy for patients diagnosed with prostate cancer thanks to the ease of localising FMs on photon-based imaging, like Computed Tomography (CT) images. Recently, Magnetic Resonance (MR)-only radiotherapy has been proposed to simplify the workflow and reduce possible systematic uncertainties. A critical, determining factor in the accuracy of such an MR-only simulation will be accurate FM localisation using solely MR images.

PURPOSE

The aim of this study is to evaluate the performances of manual MR-based FM localisation within a clinical environment.

METHODS

We designed a study in which 5 clinically involved radiation therapy technicians (RTTs) independently localised the gold FMs implanted in 16 prostate cancer patients in two scenarios: employing a single MR sequence or a combination of sequences. Inter-observer precision and accuracy were assessed for the two scenarios for localisation in terms of 95% limit of agreement on single FMs (LoA)/ centre of mass (LoA _CM) and inter-marker distances (IDs), respectively.

RESULTS

The number of precisely located FMs (LoA <2 mm) increased from 38/48 to 45/48 FMs when localisation was performed using multiple sequences instead of single one. When performing localisation on multiple sequences, imprecise localisation of the FMs (3/48 FMs) occurred for 1/3 implanted FMs in three different patients. In terms of precision, we obtained LoA _CM within 0.25 mm in all directions over the precisely located FMs. In terms of accuracy, IDs difference of manual MR-based localisation versus CT-based localisation was on average (±1 STD) 0.6 ±0.6 mm.

CONCLUSIONS

For both the investigated scenarios, the results indicate that when FM classification was correct, the precision and accuracy are high and comparable to CT-based FM localisation. We found that use of multiple sequences led to better localisation performances compared with the use of single sequence. However, we observed that, due to the presence of calcification and motion, the risk of mislocated patient positioning is still too high to allow the sole use of manual FM localisation. Finally, strategies to possibly overcome the current challenges were proposed.