Quantitative dual-energy CT material decomposition of holmium microspheres: local concentration determination evaluated in phantoms and a rabbit tumor model

Estimation of renal function using iodine maps in dual-energy spectral computed tomography urography: a feasibility and accuracy study

PURPOSE

To explore the feasibility of measuring glomerular filtration rate (GFR) using iodine maps in dual-energy spectral computed tomography urography (DEsCTU) and correlate them with the estimated GFR (eGFR) based on the equation of creatinine-cystatin C.

MATERIALS AND METHODS

One hundred and twenty-eight patients referred for DEsCTU were retrospectively enrolled. The DEsCTU protocol included non-contrast, nephrographic, and excretory phase imaging. The CT-derived GFR was calculated using the above 3-phase iodine maps (CT-GFRiodine) and 120 kVp-like images (CT-GFR120kvp) separately. CT-GFRiodine and CT-GFR120kvp were compared with eGFR using paired t-test, correlation analysis, and Bland-Altman plots. The receiver operating characteristic curves were used to test the renal function diagnostic performance with CT-GFR120kvp and CT-GFRiodine.

RESULTS

The difference between eGFR (89.91 ± 18.45 ml·min-1·1.73 m-2) as reference standard and CT-GFRiodine (90.06 ± 20.89 ml·min-1·1.73 m-2) was not statistically significant, showing excellent correlation (r = 0.88, P < 0.001) and agreement (± 19.75 ml·min-1·1.73 m-2, P = 0.866). The correlation between eGFR and CT-GFR120kvp (66.13 ± 19.18 ml·min-1·1.73 m-2) was poor (r = 0.36, P < 0.001), and the agreement was poor (± 40.65 ml·min-1·1.73 m-2, P < 0.001). There were 62 patients with normal renal function and 66 patients with decreased renal function based on eGFR. The CT-GFRiodine had the largest area under the curve (AUC) for distinguishing between normal and decreased renal function (AUC = 0.951).

CONCLUSION

The GFR can be calculated accurately using iodine maps in DEsCTU. DEsCTU could be a non-invasive and reliable one-stop-shop imaging technique for evaluating both the urinary tract morphology and renal function.

Intraprocedural MRI-based dosimetry during transarterial radioembolization of liver tumours with holmium-166 microspheres (EMERITUS-1): a phase I trial towards adaptive, image-controlled treatment delivery

PURPOSE

Transarterial radioembolization (TARE) is a treatment for liver tumours based on injection of radioactive microspheres in the hepatic arterial system. It is crucial to achieve a maximum tumour dose for an optimal treatment response, while minimizing healthy liver dose to prevent toxicity. There is, however, no intraprocedural feedback on the dose distribution, as nuclear imaging can only be performed after treatment. As holmium-166 (¹⁶⁶Ho) microspheres can be quantified with MRI, we investigate the feasibility and safety of performing ¹⁶⁶Ho TARE within an MRI scanner and explore the potential of intraprocedural MRI-based dosimetry.

METHODS

Six patients were treated with ¹⁶⁶Ho TARE in a hybrid operating room. Per injection position, a microcatheter was placed under angiography guidance, after which patients were transported to an adjacent 3-T MRI system. After MRI confirmation of unchanged catheter location, ¹⁶⁶Ho microspheres were injected in four fractions, consisting of 10%, 30%, 30% and 30% of the planned activity, alternated with holmium-sensitive MRI acquisition to assess the microsphere distribution. After the procedures, MRI-based dose maps were calculated from each intraprocedural image series using a dedicated dosimetry software package for ¹⁶⁶Ho TARE.

RESULTS

Administration of ¹⁶⁶Ho microspheres within the MRI scanner was feasible in 9/11 (82%) injection positions. Intraprocedural holmium-sensitive MRI allowed for tumour dosimetry in 18/19 (95%) of treated tumours. Two CTCAE grade 3-4 toxicities were observed, and no adverse events were attributed to treatment in the MRI. Towards the last fraction, 4/18 tumours exhibited signs of saturation, while in 14/18 tumours, the microsphere uptake patterns did not deviate from the linear trend.

CONCLUSION

This study demonstrated feasibility and preliminary safety of a first in-human application of TARE within a clinical MRI system. Intraprocedural MRI-based dosimetry enabled dynamic insight in the microsphere distribution during TARE. This proof of concept yields unique possibilities to better understand microsphere distribution in vivo and to potentially optimize treatment efficacy through treatment personalization.

REGISTRATION

Clinicaltrials.gov, identifier NCT04269499, registered on February 13, 2020 (retrospectively registered).

Development of an MRI-Guided Approach to Selective Internal Radiation Therapy Using Holmium-166 Microspheres

Simple Summary

Selective internal radiation therapy (SIRT) is a treatment for patients with liver cancer that involves the injection of radioactive microspheres into the liver artery. For a successful treatment, it is important that tumours are adequately covered with these microspheres; however, there is currently no method to assess this intraoperatively. As holmium microspheres are paramagnetic, MRI can be used to visualize the holmium deposition directly after administration, and possibly to adapt the treatment if necessary. In order to exploit this advantage and provide a personally optimized approach to SIRT, the administration could ideally be performed within a clinical MRI scanner. It is, however, unclear whether all materials (catheters, administration device) used during the procedure are safe for use in the MRI suite. Additionally, we explore the capability of MRI to visualize the microspheres in near real-time during injection, which would be a requirement for successful MRI-guided treatment. We further illustrate our findings with an initial patient case.

Abstract

Selective internal radiation therapy (SIRT) is a treatment modality for liver tumours during which radioactive microspheres are injected into the hepatic arterial tree. Holmium-166 (¹⁶⁶Ho) microspheres used for SIRT can be visualized and quantified with MRI, potentially allowing for MRI guidance during SIRT. The purpose of this study was to investigate the MRI compatibility of two angiography catheters and a microcatheter typically used for SIRT, and to explore the detectability of ¹⁶⁶Ho microspheres in a flow phantom using near real-time MRI. MR safety tests were performed at a 3 T MRI system according to American Society for Testing of Materials standard test methods. To assess the near real-time detectability of ¹⁶⁶Ho microspheres, a flow phantom was placed in the MRI bore and perfused using a peristaltic pump, simulating the flow in the hepatic artery. Dynamic MR imaging was performed using a 2D FLASH sequence during injection of different concentrations of ¹⁶⁶Ho microspheres. In the safety assessment, no significant heating (ΔT_max 0.7 °C) was found in any catheter, and no magnetic interaction was found in two out of three of the used catheters. Near real-time MRI visualization of ¹⁶⁶Ho microsphere administration was feasible and depended on holmium concentration and vascular flow speed. Finally, we demonstrate preliminary imaging examples on the in vivo catheter visibility and near real-time imaging during ¹⁶⁶Ho microsphere administration in an initial patient case treated with SIRT in a clinical 3 T MRI. These results support additional research to establish the feasibility and safety of this procedure in vivo and enable the further development of a personalized MRI-guided approach to SIRT.