A guide to 90Y radioembolization and its dosimetry

New frontiers in radioembolization

Radioembolization is a locoregional transarterial therapy that combines radionuclide and micron-sized beads to deliver radiation internally to the target tumors based on the arterial blood flow. While initially developed as a palliative treatment option, radioembolization is now used for curative intent treatment, neoadjuvant therapy, and method to downstage or bridge for liver transplant. Radioembolization has become increasingly utilized and is an important therapeutic option for the management of hepatocellular carcinoma and liver metastasis. This article provides an overview of the techniques, challenges, and novel developments in radioembolization, including new dosimetry techniques, radionuclides, and new target tumors.

Arterial hypoperfusion as a negative predictive marker for primary hepatic malignancies treated with Y-90 glass microsphere transarterial radioembolization

Background

Radioembolization with yttrium-90 (Y-90) is utilized to treat primary liver malignancies. The efficacy of this intra-arterial therapy in arterially hypoperfused tumors is not known.

Methods

We reviewed data of patients with primary liver tumors treated with Y-90 prescription doses of at least 150 Gy. Baseline patient characteristics, treatment history, imaging-based tumor response assessments, and clinical outcome metrics were recorded. Tumors were classified as arterially hyperperfused versus hypoperfused on post-TARE Y-90 SPECT/CTs or pre-TARE hepatic perfusion SPECT/CTs. Perfusion status was correlated with tumor response assessments and clinical outcomes. Cox proportional hazards models were utilized to compare survival and progression-free survival. Inverse probability weighting was utilized to account for clinical factors and adjusted multivariable proportional hazards analyses to examine the relationship of quantitative perfusion and cancer outcomes.

Results

Of 400 Y-90 treatments, 88 patients received a prescribed dose of at least 150 Gy and had pre- or post-treatment SPECT/CT images. 11 and 77 patients had arterially hypoperfused and hyperperfused lesions, respectively. On dedicated liver MRI or CT at 3 months after Y-90, the complete response rates were 5.6% and 16.5% in the hypoperfused and hyperperfused cohort, respectively (P = 0.60). When controlling for various clinical features, including tumor histology, patients with arterially hypoperfused tumors had significantly shorter progression-free survival (HR 1.87, 95% CI - 1.03 - 3.37, P = 0.039) and greater elsewhere liver (HR 3.36, 95% CI = 1.23 - 9.20, P = 0.019) and distant failure (HR 7.64 (2.71 - 21.54, P < 0.001). In inverse probability weighted analysis, patients with arterially hypoperfused tumors had worse overall survival (P = 0.032). In the quantitative analysis, lower levels of lesion perfusion were also associated with worse clinical outcomes, again controlling for tumor histology.

Conclusion

Compared to arterially hyperperfused tumors, hypoperfused primary liver tumors treated with Y-90 may have worse clinical outcomes.

Establishing Updated Safety Standards for Independent 99mTc-MAA SPECT/CT Treatment Planning in Radioembolization

PURPOSE

Significant improvements within radioembolization imaging and dosimetry permit the development of an accurate and personalized pretreatment plan using technetium 99m-labeled macroaggregated albumin (99mTc-MAA) and single-photon emission computed tomography (SPECT) combined with anatomical CT (SPECT/CT). Despite these potential advantages, the clinical transition to pretreatment protocols with SPECT/CT is hindered by their unknown safety constraints. This study aimed to address this issue by establishing novel dose limits for 99mTc-MAA SPECT/CT to enable quantitative pretreatment planning.

METHODS AND MATERIALS

Stratification criteria to determine images most viable for dosimetry analysis were created from a cohort of 85 patients. SPECT/CT, cone beam CT, and activity calculations derived from the local deposition method were used to create an accurate pretreatment protocol. Planar and SPECT/CT images were compared using linear regression and modified Bland-Altman analyses to convert accepted planar dose limits to SPECT/CT. To validate these new dose limits, activity calculations based on SPECT/CT were compared with those calculated with the body surface area and planar methods for three treatment plans.

RESULTS

A total of 38 of 85 patients were deemed viable for dosimetry analysis. SPECT yielded greater lung shunt fractions (LSFs) than planar imaging when LSFs were <4.89%, whereas SPECT yielded lower LSFs than planar imaging when LSFs were >4.89%. Planar to SPECT/CT dose conversions were 0.76×, 0.70×, and 0.55× for the whole liver, normal liver, and lungs, respectively. Patients with SPECT LSFs ≤4.89% were safely treated with the direct application of planar lung dose limits. Activity calculations with the newly established SPECT/CT dose limits were greater than those of the body surface area method by a median range of 33.1% to 61.9% and were lower than planar-based activity calculations by a median range of 12.5% to 13.7% for the whole liver and by 29.4% to 32.2% for the normal liver.

CONCLUSIONS

This study demonstrated a safe method for translating dose limits from 99mTc-MAA planar imaging to SPECT/CT. A robust pretreatment protocol was further developed guided by the current knowledge in the field. Established SPECT/CT dose limits safely treated 97.5% of patients and permitted the application of independent pretreatment planning with 99mTc-MAA SPECT/CT.

Characterizing the voxel-based approaches in radioembolization dosimetry with reDoseMC

BACKGROUND

Yttrium-90 (90 Y $^{90}{\rm {Y}}$ ) represents the primary radioisotope used in radioembolization procedures, while holmium-166 (166 Ho $^{166}{\rm {Ho}}$ ) is hypothesized to serve as a viable substitute for90 Y $^{90}{\rm {Y}}$ due to its comparable therapeutic potential and improved quantitative imaging. Voxel-based dosimetry for these radioisotopes relies on activity images obtained through PET or SPECT and dosimetry methods, including the voxel S-value (VSV) and the local deposition method (LDM). However, the evaluation of the accuracy of absorbed dose calculations has been limited by the use of non-ideal reference standards and investigations restricted to the liver. The objective of this study was to expand upon these dosimetry characterizations by investigating the impact of image resolutions, voxel sizes, target volumes, and tissue materials on the accuracy of90 Y $^{90}{\rm {Y}}$ and166 Ho $^{166}{\rm {Ho}}$ dosimetry techniques.

METHODS

A specialized radiopharmaceutical dosimetry software called reDoseMC was developed using the Geant4 Monte Carlo toolkit and validated by benchmarking the generated90 Y $^{90}{\rm {Y}}$ kernels with published data. The decay spectra of both90 Y $^{90}{\rm {Y}}$ and166 Ho $^{166}{\rm {Ho}}$ were also compared. Multiple VSV kernels were generated for the liver, lungs, soft tissue, and bone for isotropic voxel sizes of 1 mm, 2 mm, and 4 mm. Three theoretical phantom setups were created with 20 or 40 mm activity and mass density inserts for the same three voxel sizes. To replicate the limited spatial resolutions present in PET and SPECT images, image resolutions were modeled using a 3D Gaussian kernel with a Full Width at Half Maximum (FWHM) ranging from 0 to 16 mm and with no added noise. The VSV and LDM dosimetry methods were evaluated by characterizing their respective kernels and analyzing their absorbed dose estimates calculated on theoretical phantoms. The ground truth for these estimations was calculated using reDoseMC.

RESULTS

The decay spectra obtained through reDoseMC showed less than a 1% difference when compared to previously published experimental data for energies below 1.9 MeV in the case of90 Y $^{90}{\rm {Y}}$ and less than 1% for energies below 1.5 MeV for166 Ho $^{166}{\rm {Ho}}$ . Additionally, the validation kernels for90 Y $^{90}{\rm {Y}}$ VSV exhibited results similar to those found in published Monte Carlo codes, with source dose depositions having less than a 3% error margin. Resolution thresholds (FWHM thresh s ${\rm {FWHM}}_\mathrm{thresh}{\rm {s}}$ ), defined as resolutions that resulted in similar dose estimates between the LDM and VSV methods, were observed for90 Y $^{90}{\rm {Y}}$ . They were 1.5 mm for bone, 2.5 mm for soft tissue and liver, and 8.5 mm for lungs. For166 Ho $^{166}{\rm {Ho}}$ , the accuracy of absorbed dose deposition was found to be dependent on the contributions of absorbed dose from photons. Volume errors due to variations in voxel size impacted the final dose estimates. Larger target volumes yielded more accurate mean doses than smaller volumes. For both radioisotopes, the radial dose profiles for the VSV and LDM approximated but never matched the reference standard.

CONCLUSIONS

reDoseMC was developed and validated for radiopharmaceutical dosimetry. The accuracy of voxel-based dosimetry was found to vary widely with changes in image resolutions, voxel sizes, chosen target volumes, and tissue material; hence, the standardization of dosimetry protocols was found to be of great importance for comparable dosimetry analysis.

MIDOS: a novel stochastic model towards a treatment planning system for microsphere dosimetry in liver tumors

PURPOSE

Transarterial radioembolization (TARE) procedures treat liver tumors by injecting radioactive microspheres into the hepatic artery. Currently, there is a critical need to optimize TARE towards a personalized dosimetry approach. To this aim, we present a novel microsphere dosimetry (MIDOS) stochastic model to estimate the activity delivered to the tumor(s), normal liver, and lung.

METHODS

MIDOS incorporates adult male/female liver computational phantoms with the hepatic arterial, hepatic portal venous, and hepatic venous vascular trees. Tumors can be placed in both models at user discretion. The perfusion of microspheres follows cluster patterns, and a Markov chain approach was applied to microsphere navigation, with the terminal location of microspheres determined to be in either normal hepatic parenchyma, hepatic tumor, or lung. A tumor uptake model was implemented to determine if microspheres get lodged in the tumor, and a probability was included in determining the shunt of microspheres to the lung. A sensitivity analysis of the model parameters was performed, and radiation segmentectomy/lobectomy procedures were simulated over a wide range of activity perfused. Then, the impact of using different microspheres, i.e., SIR-Sphere®, TheraSphere®, and QuiremSphere®, on the tumor-to-normal ratio (TNR), lung shunt fraction (LSF), and mean absorbed dose was analyzed.

RESULTS

Highly vascularized tumors translated into increased TNR. Treatment results (TNR and LSF) were significantly more variable for microspheres with high particle load. In our scenarios with 1.5 GBq perfusion, TNR was maximum for TheraSphere® at calibration time in segmentectomy/lobar technique, for SIR-Sphere® at 1-3 days post-calibration, and regarding QuiremSphere® at 3 days post-calibration.

CONCLUSION

This novel approach is a decisive step towards developing a personalized dosimetry framework for TARE. MIDOS assists in making clinical decisions in TARE treatment planning by assessing various delivery parameters and simulating different tumor uptakes. MIDOS offers evaluation of treatment outcomes, such as TNR and LSF, and quantitative scenario-specific decisions.

Comparison of absorbed doses to the tumoral and non-tumoral liver in HCC patients undergoing 99mTc-MAA and 90Y-microspheres radioembolization

PURPOSE

This study aimed to determine the absorbed doses in the tumoral-liver and non-tumoral liver of hepatocellular carcinoma (HCC) patients undergoing radioembolization with Yttrium-90 (90Y) resin microspheres, and compared with those derived from 99mTc-MAA using the partition model.

METHODS

A total of 42 HCC patients (28 males and 14 females, mean age 65 ± 11.51 years) who received 45 treatment sessions with 90Y-microspheres between 2016 and 2021 were included. Pre-treatment 99mTc-MAA and post-treatment 90Y-bremsstrahlung SPECT/CT were acquired for each patient. Semi-automated segmentation of regions of interest (ROIs) was performed using MIM Encore software to determine the tumor-liver ratio (TLR) encompassing the liver volume, tumoral-liver, and lungs, and verified by both nuclear medicine physician and interventional radiologist. A partition dosimetry model was used to estimate the administered activity of 90Y-microspheres and the absorbed doses to the tumoral-liver and non-tumoral liver. The student's paired t test and Bland-Altman plot were used for the statistical analysis.

RESULTS

The mean TLR values obtained from 99mTc-MAA SPECT/CT and 90Y-bremsstrahlung SPECT/CT were 4.78 ± 3.51 and 2.73 ± 1.18, respectively. The mean planning administered activity of 90Y-microspheres based on 99mTc-MAA SPECT/CT was 1.56 ± 0.80 GBq, while the implanted administered activity was 2.53 ± 1.23 GBq (p value < 0.001). The mean absorbed doses in the tumoral-liver estimated from 99mTc-MAA and 90Y-bremsstrahlung SPECT/CT were 127.44 ± 4.36 Gy and 135.98 ± 6.30 Gy, respectively. The corresponding mean absorbed doses in the non-tumoral liver were 34.61 ± 13.93 Gy and 55.04 ± 16.36 Gy.

CONCLUSION

This study provides evidence that the administered activity of 90Y-microspheres, as estimated from 90Y-bremsstrahlung SPECT/CT, was significantly higher than that estimated from 99mTc-MAA SPECT/CT resulted in increased absorbed doses in both the tumoral-liver and non-tumoral liver. However, 99mTc-MAA SPECT/CT remains a valuable planning tool for predicting the distribution of 90Y-microspheres in liver cancer treatment.

PET/CT and SPECT/CT imaging of 90Y hepatic radioembolization at therapeutic and diagnostic activity levels: Anthropomorphic phantom study

PURPOSE

Prior to 90Y radioembolization procedure, a pretherapy simulation using 99mTc-MAA is performed. Alternatively, a small dosage of 90Y microspheres could be used. We aimed to assess the accuracy of lung shunt fraction (LSF) estimation in both high activity 90Y posttreatment and pretreatment scans with isotope activity of ~100 MBq, using different imaging techniques. Additionally, we assessed the feasibility of visualising hot and cold hepatic tumours in PET/CT and Bremsstrahlung SPECT/CT images.

MATERIALS AND METHODS

Anthropomorphic phantom including liver (with two spherical tumours) and lung inserts was filled with 90Y chloride to simulate an LSF of 9.8%. The total initial activity in the liver was 1451 MBq, including 19.4 MBq in the hot sphere. Nine measurement sessions including PET/CT, SPECT/CT, and planar images were acquired at activities in the whole phantom ranging from 1618 MBq down to 43 MBq. The visibility of the tumours was appraised based on independent observers' scores. Quantitatively, contrast-to-noise ratio (CNR) was calculated for both spheres in all images.

RESULTS

LSF estimation. For high activity in the phantom, PET reconstructions slightly underestimated the LSF; absolute difference was <1.5pp (percent point). For activity <100 MBq, the LSF was overestimated. Both SPECT and planar scintigraphy overestimated the LSF for all activities. Lesion visibility. For SPECT/CT, the cold tumour proved too small to be discernible (CNR <0.5) regardless of the 90Y activity in the liver, while hot sphere was visible for activity >200 MBq (CNR>4). For PET/CT, the cold tumour was only visible with the highest 90Y activity (CNR>4), whereas the hot one was seen for activity >100 MBq (CNR>5).

CONCLUSIONS

PET/CT may accurately estimate the LSF in a 90Y posttreatment procedure. However, at low activities of about 100 MBq it seems to provide unreliable estimations. PET imaging provided better visualisation of both hot and cold tumours.

MIRD Pamphlet No. 29: MIRDy90-A 90Y Research Microsphere Dosimetry Tool

90Y-microsphere radioembolization has become a well-established treatment option for liver malignancies and is one of the first U.S. Food and Drug Administration-approved unsealed radionuclide brachytherapy devices to incorporate dosimetry-based treatment planning. Several different mathematical models are used to calculate the patient-specific prescribed activity of 90Y, namely, body surface area (SIR-Spheres only), MIRD single compartment, and MIRD dual compartment (partition). Under the auspices of the MIRDsoft initiative to develop community dosimetry software and tools, the body surface area, MIRD single-compartment, MIRD dual-compartment, and MIRD multicompartment models have been integrated into a MIRDy90 software worksheet. The worksheet was built in MS Excel to estimate and compare prescribed activities calculated via these respective models. The MIRDy90 software was validated against available tools for calculating 90Y prescribed activity. The results of MIRDy90 calculations were compared with those obtained from vendor and community-developed tools, and the calculations agreed well. The MIRDy90 worksheet was developed to provide a vetted tool to better evaluate patient-specific prescribed activities calculated via different models, as well as model influences with respect to varying input parameters. MIRDy90 allows users to interact and visualize the results of various parameter combinations. Variables, equations, and calculations are described in the MIRDy90 documentation and articulated in the MIRDy90 worksheet. The worksheet is distributed as a free tool to build expertise within the medical physics community and create a vetted standard for model and variable management.

AAPM Medical Physics Practice Guideline 14.a: Yttrium-90 microsphere radioembolization

Radioembolization using Yttrium-90 (90 Y) microspheres is widely used to treat primary and metastatic liver tumors. The present work provides minimum practice guidelines for establishing and supporting such a program. Medical physicists play a key role in patient and staff safety during these procedures. Products currently available are identified and their properties and suppliers summarized. Appropriateness for use is the domain of the treating physician. Patient work up starts with pre-treatment imaging. First, a mapping study using Technetium-99m (Tc-99m ) is carried out to quantify the lung shunt fraction (LSF) and to characterize the vascular supply of the liver. An MRI, CT, or a PET-CT scan is used to obtain information on the tumor burden. The tumor volume, LSF, tumor histology, and other pertinent patient characteristics are used to decide the type and quantity of 90 Y to be ordered. On the day of treatment, the appropriate dose is assayed using a dose calibrator with a calibration traceable to a national standard. In the treatment suite, the care team led by an interventional radiologist delivers the dose using real-time image guidance. The treatment suite is posted as a radioactive area during the procedure and staff wear radiation dosimeters. The treatment room, patient, and staff are surveyed post-procedure. The dose delivered to the patient is determined from the ratio of pre-treatment and residual waste exposure rate measurements. Establishing such a treatment modality is a major undertaking requiring an institutional radioactive materials license amendment complying with appropriate federal and state radiation regulations and appropriate staff training commensurate with their respective role and function in the planning and delivery of the procedure. Training, documentation, and areas for potential failure modes are identified and guidance is provided to ameliorate them.

Hepatopulmonary Shunt Ratio Verification Model for Transarterial Radioembolization

INTRODUCTION

The most important toxicity of transarterial radioembolization therapy applied in liver malignancies is radiation pneumonitis and fibrosis due to hepatopulmonary shunt of Yttrium-90 (90Y) microspheres. Currently, Technetium-99m macroaggregated albumin (99mTc-MAA) scintigraphic images are used to estimate lung shunt fraction (LSF) before treatment. The aim of this study was to create a phantom to calculate exact LFS rates according to 99mTc activities in the phantom and to compare these rates with LSF values calculated from scintigraphic images.

MATERIALS AND METHODS

A 3D-printed lung and liver phantom containing two liver tumors was developed from Polylactic Acid (PLA) material, which is similar to the normal-sized human body in terms of texture and density. Actual %LSFs were calculated by filling phantoms and tumors with 99mTc radionuclide. After the phantoms were placed in the water tank made of plexiglass material, planar, SPECT, and SPECT/CT images were obtained. The actual LSF ratio calculated from the activity amounts filled into the phantom was used for the verification of the quantification of scintigraphic images and the results obtained by the Simplicity90YTM method.

RESULTS

In our experimental model, LSFs calculated from 99mTc activities filled into the lungs, normal liver, small tumor, and large tumor were found to be 0%, 6.2%, 10.8%, and 16.9%. According to these actual LSF values, LSF values were calculated from planar, SPECT/CT (without attenuation correction), and SPECT/CT (with both attenuation and scatter correction) scintigraphic images of the phantom. In each scintigraphy, doses were calculated for lung, small tumor, large tumor, normal liver, and Simplicity90YTM. The doses calculated from planar and SPECT/CT (NoAC+NoSC) images were found to be higher than the actual doses. The doses calculated from SPECT/CT (with AC+with SC) images and Simplicity90YTM were found to be closer to the real dose values.

CONCLUSION

LSF is critical in dosimetry calculations of 90Y microsphere therapy. The newly introduced hepatopulmonary shunt phantom in this study is suitable for LSF verification for all models/brands of SPECT and SPECT/CT devices.

Measurement of the Tumor-to-Normal Ratio for Radioembolization of Hepatocellular Carcinoma: A Prospective Study Comparing 2-Dimensional Perfusion Angiography, Technetium-99m Macroaggregated Albumin, and Yttrium-90 SPECT/CT

PURPOSE

To calculate the preradioembolic tumor-to-normal (T:N) ratio in hepatocellular carcinoma (HCC) using 2-dimensional (2D) perfusion angiography and compare it with that calculated using technetium-99m macroaggregated albumin (99mTc MAA) single-photon emission computed tomography (SPECT)/computed tomography (CT).

MATERIALS AND METHODS

This prospective single-arm study enrolled 15 participants with HCC who underwent 2D perfusion angiography immediately before the enrollment and with the microcatheter located at the same location as 99mTc MAA injection, after which SPECT/CT was performed. Quantitative digital subtraction angiography was used to calculate the area under the curve for the tumor and normal hepatic parenchyma and subsequently calculate the T:N ratio. The T:N ratio was calculated from the 99mTc MAA SPECT/CT and post-yttrium-90 bremsstrahlung SPECT/CT using dosimetry software.

RESULTS

The mean participant age was 64.1 years ± 9.8, and the study included 14 (93%) men and 1 (7%) woman. The mean tumor size was 4.1 cm (SD ± 2.4), and all participants received segmental treatments with glass microspheres. The mean T:N ratio calculated by 99mTc MAA SPECT/CT was 2.28 (SD ± 0.89) vs 2.25 (SD ± 0.99) calculated by 2D perfusion angiography (P = .45). For the 13 participants who underwent selective internal radiation therapy (transarterial radioembolization), there was no significant difference between the T:N ratios calculated by 2D perfusion angiography and post-90Y SPECT/CT (2.25 [SD ± 1.05] vs 1.91 [SD ± 0.39]; P = .12).

CONCLUSIONS

The T:N ratio calculated by 2D perfusion angiography correlated well with that calculated by 99mTc MAA SPECT/CT.

A single centre intercomparison between commercial treatment planning systems for 90Y radioembolization using virtual and experimental phantoms

INTRODUCTION

Dedicated Treatment Planning Systems (TPSs) were developed to personalize 90Y-transarterial radioembolization. This study evaluated the agreement among four commercial TPSs assessing volumes of interest (VOIs) volumes and dose metrics.

METHODS

A homogeneous (EH) and an anthropomorphic phantom with hot and cold inserts (EA) filled with 99mTc-pertechnetate were acquired with a SPECT/CT scanner. Their virtual versions (VH and VA, respectively) and a phantom with activity inside a single voxel (VK) were generated by an in-house MATLAB script. Images and delineated VOIs were imported into the TPSs to compute voxel-based absorbed dose distributions with various dose deposition approaches: local deposition method (LDM) and dose kernel convolution (DKC) with/without local density correction (LDC). VOI volumes and mean absorbed doses were assessed against their median value across TPSs. Dose-volume histograms (DVHs) and VK-derived dose profiles were evaluated.

RESULTS

Small (<2.1 %) and large (up to 42.4 %) relative volume differences were observed on large (>500 ml) and small VOIs, respectively. Mean absorbed doses relative differences were < 3 % except for small VOIs with steep dose gradients (up to 89.1 % in the VA Cold Sphere VOI). Within the same TPS, LDC negligibly affected the mean absorbed dose, while DKC and LDM showed differences up to 63 %. DHVs were mostly overlapped in experimental phantoms, with some differences in the virtual versions. Dose profiles agreed within 1 %.

CONCLUSION

TPSs showed an overall good agreement except for small VOI volumes and mean absorbed doses of VOIs with steep dose gradients. These discrepancies should be considered in the dosimetry uncertainty assessment, thus requiring an appropriate harmonization.

Efficacy of Selective Internal Radiation Therapy for Hepatocellular Carcinoma Post-Incomplete Response to Chemoembolization

Hepatocellular carcinoma (HCC) is one of the most common neoplasms worldwide and the third most common cause of cancer-related death. Several liver-targeted intra-arterial therapies are available for unresectable HCC, including selective internal radiation therapy (SIRT) and trans-arterial chemoembolization (TACE). Those two are the most used treatment modalities in localized non-operable HCC. TACE is the treatment option for patients with stage B, according to the BCLC staging system. In contrast, SIRT does not have an official role in the treatment algorithm, but recent studies showed promising outcomes in patients treated with SIRT. Although TACE is globally a safe procedure, it might provoke several vascular complications such as spasms, inflammatory constriction, and, in severe cases, occlusion, dissection, or collateralization. Hence, it is acclaimed that those complications could restrain the targeted response of the radio-embolization when we use it as second-line therapy post TACE. In this study, we will assess the efficacity of SIRT using Yttrium 90 Microspheres post incomplete or failure response to TACE. In our retrospective study, we had 23 patients who met the inclusion criteria. Furthermore, those patients have been followed radiologically and biologically. Then, we evaluated the therapeutic effect according to the mRECIST criteria, in addition to the personalized dose analysis. We found 8 patients were treated with TheraSphere®, with a median tumor absorbed dose of 445 Gy, while 15 received SIR-Spheres® treatment with a mean tumor dose of 268 Gy. After radiological analysis, 56.5% of the patients had a complete response, and 17.3% showed partial response, whereas 13% had stable disease and 13% had progressive disease. For patients treated with SIRT after an incomplete response or failure to TACE, we found an objective response rate of 73.8%. Despite the known vascular complications of TACE, SIRT can give a favorable response.

Current status of yttrium-90 microspheres radioembolization in primary and metastatic liver cancer

Liver malignancy, including primary liver cancer and metastatic liver cancer, has become one of the most common causes of cancer-related death worldwide due to the high malignant degree and limited systematic treatment strategy. Radioembolization with yttrium-90 (90Y)-loaded microspheres is a relatively novel technology that has made significant progress in the local treatment of liver malignancy. The different steps in the extensive work-up of radioembolization for patients with an indication for treatment with 90Y microspheres, from patient selection to follow up, both technically and clinically, are discussed in this paper. It describes the application and development of 90Y microspheres in the treatment of liver cancer.

A personalized Monte Carlo study of tumor and critical organ doses for trans-arterial radioembolization patients

Trans-arterial radioembolization (TARE) is an intra-arterial treatment method for liver malignancies. In this procedure, the therapeutic tumor dose is significant for predicting the treatment effectiveness while the dose absorbed in an organ at risk provides an understanding of its tolerance to radiation. This study proposes a Monte Carlo (MC) approach for determining absorbed organ doses for patients undergoing TARE treatment. The technique is based on the use of a voxel-based partial body model generated for each patient from his/her anatomical image data to represent the critical body structures more realistically. These structures are first segmented from image slices to create an image block which is then incorporated into a radiation transport package (MCNP6.2) to perform MC simulations. When used along with the parameters specific to a patient's treatment, such as lung-shunt factor, tumor-to-normal liver ratio, fractional uptakes, and administered activity, this approach allowed more accurate simulation of radiation interactions and hence provided absorbed doses specific to a TARE patient. The MC method also calculated the absorbed doses in organs or tissues that were close to target tissues for which the Medical Internal Radiation Dose Committee (MIRD) formalism makes no predictions. MIRD calculations were found to overestimate the absorbed doses by as much as 11% in lungs, 5% in liver, and 20% in tumor volumes. This raises concerns about the treatment's efficacy when estimating the correct activity to be administered to a patient. When each patient simulation was repeated with a90Y source spectrum to reflect the distribution of varying beta energies, the liver and the lungs were observed to receive relatively lower doses than those obtained with monoenergetic beta particles. Thus, it can be stated that the approach adopted in this study offers a more precise model of the patient's critical tissues and serves as a personalized dosimetric tool for TARE treatment planning.

Using Deep Learning to Predict Treatment Response in Patients with Hepatocellular Carcinoma Treated with Y90 Radiation Segmentectomy

Treatment of hepatocellular carcinoma (HCC) with Y90 radioembolization segmentectomy (Y90-RE) demonstrates a tumor dose-response threshold, where dose estimates are highly dependent on accurate SPECT/CT acquisition, registration, and reconstruction. Any error can result in distorted absorbed dose distributions and inaccurate estimates of treatment success. This study improves upon the voxel-based dosimetry model, one of the most accurate methods available clinically, by using a deep convolutional network ensemble to account for the spatially variable uptake of Y90 within a treated lesion. A retrospective analysis was conducted in patients with HCC who received Y90-RE at a single institution. Seventy-seven patients with 103 lesions met the inclusion criteria: three or fewer tumors, pre- and post treatment MRI, and no prior Y90-RE. Lesions were labeled as complete (n = 57) or incomplete response (n = 46) based on 3-month post treatment MRI and divided by medical record number into a 20% hold-out test set and 80% training set with 5-fold cross-validation. Slice-wise predictions were made from an average ensemble of models and thresholds from the highest accuracy epochs across all five folds. Lesion predictions were made by thresholding all slice predictions through the lesion. When compared to the voxel-based dosimetry model, our model had a higher F1-score (0.72 vs. 0.2), higher accuracy (0.65 vs. 0.60), and higher sensitivity (1.0 vs. 0.11) at predicting complete treatment response. This algorithm has the potential to identify patients with treatment failure who may benefit from earlier follow-up or additional treatment.

Minimally Invasive Treatment Options for Hepatic Uveal Melanoma Metastases

Uveal melanoma is one of the most common primary intraocular malignancies that accounts for about 85% of all ocular melanomas. The pathophysiology of uveal melanoma is distinct from cutaneous melanoma and has separate tumor profiles. The management of uveal melanoma is largely dependent on the presence of metastases, which confers a poor prognosis with a one-year survival reaching only 15%. Although a better understanding of tumor biology has led to the development of novel pharmacologic agents, there is increasing demand for minimally invasive management of hepatic uveal melanoma metastases. Multiple studies have already summarized the systemic therapeutic options available for metastatic uveal melanoma. This review covers the current research for the most prevalent locoregional treatment options for metastatic uveal melanoma including percutaneous hepatic perfusion, immunoembolization, chemoembolization, thermal ablation, and radioembolization.

Personalized 90 Y-resin microspheres dose determination: a retrospective study on the impact of dosimetry software on the treatment of patients with selective internal radiotherapy

INTRODUCTION

The calculation of resin yttrium-90 ( 90 Y-) microspheres activity for selective internal radiotherapy (SIRT) needs to be investigated.

METHODS AND MATERIALS

Analyses using Simplicit 90 Y (Boston Scientific, Natick, Massachusetts, USA) dosimetry software were performed to determine the concordance between the absorbed doses to the tumor (D T1 and D T2 ) and healthy liver (D N1 and D N2 ) during the pre-treatment and the post-treatment phases. An optimized calculation of the activity of 90 Y-microspheres performed using dosimetry software was applied retrospectively to assess the impact of this calculation method on the treatment.

RESULTS

D T1 ranged from 38.8 to 372 Gy, with a mean value of 128.9 ± 73.6 Gy and median of 121.2 Gy [interquartile range (IQR): 81.7-158.8 Gy]. The median D N1 and D N2 was 10.5 Gy (IQR: 5.8-17.6). A significant correlation was between D T1 and D T2 ( r  = 0.88, P  < 0.001) and D N1 and D N2 ( r  = 0.96, P  < 0.001). The optimized activities were calculated; the target dose to the tumor compartment was 120 Gy. No activity reduction was applied in accordance with the tolerance of the healthy liver. Optimization of the microspheres dosages would have resulted in a significant increase in activity for nine treatments (0.21-2.54 GBq) and a reduction for seven others (0.25-0.76 GBq).

CONCLUSIONS

The development of customized dosimetry software adapted to clinical practice makes it possible to use dosimetry to optimize the dosage for each patient.

Insights into handling and delivery of Y-90 radioembolization therapies

Introduction

The use of Y-90 radioembolization techniques has become a standard tool for the treatment of liver cancer and metastatic diseases that result in liver lesions. As there are only two approved forms of radioembolization therapy, the procedures for use are also fairly standardized even though exact international and interdepartmental procedures can vary. What has been less published over the years are the nuanced differences in delivery techniques and handling of the two available Y90 radioembolization therapies. This paper seeks to examine various aspects of delivery techniques, product handling, and radiation exposure that differ between the available and approved products. Understanding these differences can assist with providing more efficient treatment, confirmation of accurate therapy, more informed handling of the products, and improved training of physicians and other hospital staff.

Methods

Two commercially available and approved radioembolization devices were compared to assess nuanced, but key differences between the available products regarding therapy delivery, handling of the products, and radiation exposure to patients and staff. This work is broken into two sections: (1) Therapy Delivery, (2) Radiation Safety. Therapy delivery characteristics were assessed by using an external radiation detector system with detectors placed inside of each delivery system facing the dose vial and on the output catheter lines to the patient. Additional detectors were placed near the liver of the patient and on top of the foot to measure extremities. Data were acquired continuously throughout therapy delivery to collect time activity curves (TACs) for the characterization of each therapy. These data were analyzed to assess if (a) real-time monitoring of radiation could be used to provide an accurate assessment of residual dose before the patient leaves the procedure room, and (b) can dose delivery characteristics be observed that enable improved training and quality control. Calculation of residual dose using the external detector TACs was performed by analyzing initial and final activity peaks to determine measured count rate differences. Radiation safety aspects were assessed by monitoring radiation exposure to staff handling each of the available therapy products. Nuclear medicine technologists and interventional radiology physician body and hand doses were measured for each delivered therapy using standard body and ring dosimeters. The TACs noted above collected for the liver and extremities were used to assess if any off-target or leached Y90 activity could be detected for each therapy. Blood was collected at times before, during, and after treatment and then counted on a gamma counter to assess differences in free Y90 circulating in the blood. Each patient in this study also received a post-treatment whole-body PET/CT at 2-4 h post-infusion to assess for any aggregate free Y90 deposition that may have resulted from circulating free Y90 in the subject following therapy.

Results

Calculations of residual dose in the vial following therapy using the real-time detection methods resulted in values that were not statistically different from the values calculated by nuclear medicine following the procedure ( p > 0.05 ). Real-time collection of dose delivery data enabled observation of key characteristics related to each delivery method. For SIR-spheres procedures, the cycle of pushing the dose and visualizing with fluoro can easily be seen with each push resulting in a smaller and smaller peak with intermittent fluoroscopy pulses. TheraSpheres infusions show a rapid bolus with nearly all of the measurable injected activity being infused in the first push of the dose. Staff radiation exposure assessments showed statistically significant differences between glass and resin spheres for hand doses of physicians and technologists (p > 0.05), but no statistical difference between body doses for both products ( p > 0.05 ). Assessments of free Y90 circulating during therapy showed that patients undergoing therapies with resin spheres had post-infusion blood levels that were 120% higher than pre-infusion levels while glass sphere therapy patients only saw a 7% rise in post-infusion blood levels. The coefficients of variation (COVs) across glass sphere measurements pre, during, and post, were only 0.008 while resin sphere measures saw much greater variability with a COV of 0.45. Both glass and resin therapies showed blood levels at 2-4 h post-injection to be similar to levels measured pre-injection. Neither therapy showed any signs of focal aggregation at 2-4 h post-infusion on whole-body PET/CT.

Conclusion

Although glass and resin radioembolization therapies are similar, they both have unique characteristics related to their administration and handling by staff. Understanding the nuances can assist in providing more efficient delivery, better staff education, and reducing radiation exposure to everyone involved with these therapies. The use of near real-time monitoring is feasible and can be used to obtain critical information about the delivery success of a therapy and can inform physicians on their techniques to optimize their practice as well as provide more consistent training to residents.

Smart nanoparticles and microbeads for interventional embolization therapy of liver cancer: state of the art

The process of transcatheter arterial chemoembolization is characterized by the ability to accurately deliver chemotherapy drugs with minimal systemic side effects and has become the standard treatment for unresectable intermediate hepatocellular carcinoma (HCC). However, this treatment option still has much room for improvement, one of which may be the introduction of nanomaterials, which exhibit unique functions and can be applied to in vivo tumor imaging and therapy. Several biodegradable and multifunctional nanomaterials and nanobeads have recently been developed and applied in the locoregional treatment of hepatocellular cancer. This review explores recent developments and findings in relation to micro-nano medicines in transarterial therapy for HCC, emerging strategies to improve the efficacy of delivering nano-based medicines, and expounding prospects for clinical applications of nanomaterials.

Voxel-based dosimetry predicting treatment response and related toxicity in HCC patients treated with resin-based Y90 radioembolization: a prospective, single-arm study

BACKGROUND

There is an increasing body of evidence indicating Y90 dose thresholds for tumor response and treatment-related toxicity. These thresholds are poorly studied in resin Y90, particularly in hepatocellular carcinoma (HCC).

PURPOSE

To evaluate the efficacy of prospective voxel-based dosimetry for predicting treatment response and adverse events (AEs) in patients with HCC undergoing resin-based Y90 radioembolization.

MATERIALS AND METHODS

This correlative study was based on a prospective single-arm clinical trial (NCT04172714), which evaluated the efficacy of low/scout (555 MBq) activity of resin-based Y90 for treatment planning. Partition model was used with goal of tumor dose (TD) > 200 Gy and non-tumoral liver dose (NTLD) < 70 Gy for non-segmental therapies. Single compartment dose of 200 Gy was used for segmentectomies. Prescribed Y90 activity minus scout activity was administered for therapeutic Y90 followed by Y90-PET/CT. Sureplan® (MIM Software, Cleveland, OH) was used for dosimetry analysis. Treatment response was evaluated at 3 and 6 months. Receiver operating characteristic curve determined TD response threshold for objective response (OR) and complete response (CR) as well as non-tumor liver dose (NTLD) threshold that predicted AEs.

RESULTS

N = 30 patients were treated with 33 tumors (19 segmental and 14 non-segmental). One patient died before the first imaging, and clinical follow-up was excluded from this analysis. Overall, 26 (81%) of the tumors had an OR and 23 (72%) had a CR. A mean TD of 253 Gy predicted an OR with 92% sensitivity and 83% specificity (area under the curve (AUC = 0.929, p < 0.001). A mean TD of 337 Gy predicted a CR with 83% sensitivity and 89% specificity (AUC = 0.845, p < 0.001). A mean NTLD of 81 and 87 Gy predicted grade 3 AEs with 100% sensitivity and 100% specificity in the non-segmental cohort at 3- and 6-month post Y90, respectively.

CONCLUSION

In patients with HCC undergoing resin-based Y90, there are dose response and dose toxicity thresholds directly affecting outcomes.

CLINICAL TRIAL NUMBER

NCT04172714.

Transarterial Selective Internal Radiation Therapy with Yttrium-90 for Liver Metastatic Urothelial Carcinoma of the Ureter as a Bridging Therapy to Immunotherapy: A Case Report with a 10-Year Follow-Up

Primary transitional cell carcinoma of the ureter is a rare type of cancer with metastasis presented in approximately 25% at diagnosis. Due to its rarity and poor prognosis, the management of this neoplasm is still controversial, and the development of new therapies is of uttermost importance. Herein, we describe a case of a 54-year-old patient diagnosed with transitional cell carcinoma of the left ureter submitted to left nephroureterectomy (pT3N2M0) and methotrexate, vinblastine, doxorubicin, and cisplatin adjuvant chemotherapy. A single liver metastasis was detected and combination chemotherapy with gemcitabine and carboplatin was initiated along with stereotactic body radiation therapy. Despite these 2 previous chemotherapy regimens, the patient presented disease progression and transarterial selective internal radiation therapy (SIRT) with yttrium-90 was indicated. This locoregional treatment was performed with the administration of 1.2 GBq yttrium-90 resin microspheres (SIR-Spheres®, Sirtex Medical Limited, Sydney, NSW, Australia) into the right hepatic artery. Another systemic treatment was immunotherapy using nivolumab with excellent tolerability. After 10 years of follow-up, at the last clinical evaluation, the patient had no clinical symptoms and the last imaging follow-up using positron emission tomography-computed tomography scan showed complete response. This report introduces upper urinary tract urothelial carcinoma as a distinct type of malignancy in which SIRT can be safely implemented. As a transition method to nivolumab, it was successful. There might be a potential therapeutic synergism between these 2 treatment modalities.

Detection of Shortwave-Infrared Cerenkov Luminescence from Medical Isotopes

Medical radioisotopes produce Cerenkov luminescence (CL) from charged subatomic particles (β+/-) traveling faster than light in dielectric media (e.g., tissue). CL is a blue-weighted and continuous emission, decreasing proportionally to increasing wavelength. CL imaging (CLI) provides an economic PET alternative with the advantage of also being able to image β- and α emitters. Like any optical modality, CLI is limited by the optical properties of tissue (scattering, absorption, and ambient photon removal). Shortwave-infrared (SWIR, 900-1700 nm) CL has been detected from MeV linear accelerators but not yet from keV medical radioisotopes. Methods: Indium-gallium-arsenide sensors and SWIR lenses were mounted onto an ambient light-excluding preclinical enclosure. An exposure and processing pipeline was developed for SWIR CLI and then performed across 6 radioisotopes at in vitro and in vivo conditions. Results: SWIR CL was detected from the clinical radioisotopes 90Y, 68Ga, 18F, 89Zr, 131I, and 32P (biomedical research). SWIR CLI's advantage over visible-wavelength (VIS) CLI (400-900 nm) was shown via increased light penetration and decreased scattering at depth. The SWIR CLI radioisotope sensitivity limit (8.51 kBq/μL for 68Ga), emission spectrum, and ex vivo and in vivo examples are reported. Conclusion: This work shows that radioisotope SWIR CLI can be performed with unmodified commercially available components. SWIR CLI has significant advantages over VIS CLI, with preserved VIS CLI features such as radioisotope radiance levels and dose response linearity. Further improvements in SWIR optics and technology are required to enable widespread adoption.

Simplification of dosimetry in 90Y-radioembolization therapy by dual planar images

AIM

The purpose was to provide a practical and effective method for performing reliable ⁹⁰Y dosimetry based on ^99mTc-MAA and SPEC/CT. The impact of scatter correction (SC) and attenuation correction (AC) on the injected ⁹⁰Y activity, lung shunt fraction (LSF) and the delivered dose to lung and liver compartments was investigated within the scope of the study.

MATERIAL AND METHODS

Eighteen eligible patients (F: 3, M: 15) were subjected to ⁹⁰Y therapy. ^99mTc-MAA (111-222 MBq) was injected into the targeted liver, followed by whole-body scan (WBS) with peak-window at 140 keV (15% width) and one down-scatter window. SPECT/CT scan was subsequently acquired encompassing lung and liver regions. The LSFs were fashioned from standard WBS LSFwb (St), scatter corrected WBS LSFwb (Sc), only scatter corrected SPECT LSFspect (NoAC-SC) and SPECT/CT with attenuation and scatter correction LSFspect (AC-SC). The absorbed doses that would be delivered to tumor and injected healthy liver were estimated using different calculation modes involving AC-SC (SPECT/CT), NoAC-SC (SPECT), NoAC-NoSC+LSFwb (SC), AC-SC + LSFwb (St), and NoAC-NoSC+LSFwb (St).

RESULTS

The average deviations (range) in LSF values between standard LSFwb (St) and those from SPECT/CT (AC-SC), SPECT (NoAC-SC), and LSFwb (SC) were - 50% (- 29/- 71), - 32% (- 8/- 67), and - 45% (- 13/80), respectively. The suggested ⁹⁰Y activity (GBq/Gy) was decreased within a range of 2-11%, 1-9%, and 2-7% by using LSFspect (AC-SC), LSFspect (NoAC-SC), and LSFwb (SC), respectively. Overall, two-sample t-test yielded no statistically significant difference (p < 0.05) in the absorbed doses to tumor and injected healthy liver between AC-SC (SPECT) and the rest of approaches with/and without AC and SC. However, a statistically significant difference (p < 0.05) was demonstrated in the lung shunt fractions and lung doses due to AC and SC. The LSFs from scatter corrected planar images LSFwb (SC) exhibited well agreement (R₂ = 0.92) with SPECT/CT (AC-SC) and there was no statistically significant difference (P_value > 0.05) between both methods.

CONCLUSION

It was deduced that SPECT/CT with attenuation and scatter correction plays a crucial role in the measurements of lung shunt fraction and dose as well as the total number of ⁹⁰Y treatments. However, the absorbed dose to tumors and injected healthy liver was minimally affected by AC and SC. Besides, a good agreement was observed between LSF datasets from SPECT/CT versus scatter corrected WBS that can be alternatively and effectively used in ⁹⁰Y dosimetry.

Accuracy and Safety of Scout Dose Resin Yttrium-90 Microspheres for Radioembolization Therapy Treatment Planning: A Prospective Single-Arm Clinical Trial

PURPOSE

To compare the accuracy and safety of 0.56 GBq resin yttrium-90 (⁹⁰Y) (scout⁹⁰Y) microspheres with those of technetium-99m macroaggregated albumin (MAA) in predicting the therapeutic ⁹⁰Y (Rx⁹⁰Y) dose for patients with hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

This prospective single-arm clinical trial (Clinicaltrials.gov: NCT04172714) recruited patients with HCC. Patients underwent same-day mapping with MAA and scout⁹⁰Y. Rx⁹⁰Y activity was administered 3 days after mapping. Using paired t test and Pearson correlation, the tumor-to-normal ratio (TNR), lung shunt fraction (LSF), predicted mean tumor dose (TD), and nontumoral liver dose (NTLD) by MAA and scout⁹⁰Y were compared with those by Rx⁹⁰Y. Bland-Altman plots compared the level of agreement between the TNR and LSF of scout⁹⁰Y and MAA with that of Rx⁹⁰Y. The safety of scout⁹⁰Y was evaluated by examining the discrepancy in extrahepatic activity between MAA and scout⁹⁰Y.

RESULTS

Thirty patients were treated using 19 segmental and 14 nonsegmental (ie, 2 contiguous segments or nonsegmental) therapies. MAA had weak LSF, moderate TNR, and moderate TD linear correlation with Rx⁹⁰Y. Scout⁹⁰Y had a moderate LSF, strong TNR, strong TD, and very strong NTLD in correlation with those of Rx⁹⁰Y. Furthermore, the TNR and LSF of scout⁹⁰Y had a stronger agreement with those of Rx⁹⁰Y than with those of MAA. In the nonsegmental subgroup, MAA had no significant correlation with the TD and NTLD of Rx⁹⁰Y, whereas scout⁹⁰Y had a very strong correlation with both of these factors. In the segmental subgroup, both MAA and scout⁹⁰Y had a strong linear correlation with the TD and NTLD of Rx⁹⁰Y.

CONCLUSIONS

Compared with MAA, scout⁹⁰Y is a more accurate surrogate for Rx⁹⁰Y biodistribution for nonsegmental therapies.

Effect of tumour involvement on activity determination of resin Yttrium-90 in selective internal radiation therapy of metastatic liver cancer

Introduction:

The study was aimed to evaluate the effect of tumour involvement on resin Yttrium-90 (Y90) activity determination for metastatic liver cancer treatment.

Methods:

One hundred and two cases of resin Y90 microsphere treatment were retrospectively studied. Body surface area (BSA) method was used in the calculation of resin Y90 activity. The total activity (TA) was calculated as a summation of activities obtained from BSA-based calculation and tumour involvement (TI). TI and TA of each case were evaluated. The contributions of TI to TA were calculated with the ratio of TI/TA.

Results:

The average contribution of TI to TA was 4·1%. The contributions were < 5·8% in 75% of the cases, < 2·2% in 50% of the cases and < 1·0% in 25% of the cases.

Conclusions:

Overall the effect of tumour involvement on the activity determination was small. The activity calculation could be simplified by neglecting TI in 25% of the cases where the activity contribution from TI was less than 1%. Contouring tumour and liver structures for TI calculation could be avoided in these cases, and the efficiency of the workflow for resin Y90 procedures could be improved.

Oncology during the New Coronavirus Infection Pandemic

The COVID-19 pandemic has served as a catalyst for a whole layer of scientific research, including in Russia, where, since 2020, international multicenter studies have been conducted on the impact of the coronavirus infection on the course of oncological diseases, as well as on the development and application of new clinical methods in oncology. In the years 2020-2022, new methods of nuclear medicine based on the targeted effect of ionizing radiation of radiopharmaceuticals began to be actively developed, in particular, new domestic radiopharmaceuticals (RPs) for diagnostics and therapy and methods of intra-arterial radioembolization developed by RPs with 90Y and 188Re of primary and metastatic tumors of various localization. New methods of radiation therapy have been introduced into clinical practice, including remote radiation therapy with "fast" neutrons, which makes it possible to overcome the resistance of a tumor to radiation and drug treatment. In addition, the search for and introduction into clinical practice of new approaches in the field of gene therapy and the use of oncolytic viruses continues. Platforms for complex pharmacogenomic analysis based on global knowledge and deep machine learning are being used in Russia, allowing for the precise selection of the most effective therapy. New multidisciplinary technologies are being developed.

Using an Assumed Lung Mass Inaccurately Estimates the Lung Absorbed Dose in Patients Undergoing Hepatic 90Yttrium Radioembolization Therapy

RATIONALE

Currently, the estimated absorbed radiation dose to the lung in ⁹⁰Y radioembolization therapy is calculated using an assumed 1 kg lung mass for all patients. The aim of this study was to evaluate whether using a patient-specific lung mass measurement for each patient rather than a generic, assumed 1 kg lung mass would change the estimated lung absorbed dose.

METHODS

A retrospective analysis was performed on 68 patients who had undergone ⁹⁰Y radioembolization therapy at our institution. Individualized lung volumes were measured manually on CT scans for each patient, and these volumes were used to calculate personalized lung masses. The personalized lung masses were used to recalculate the estimated lung absorbed dose from the ⁹⁰Y therapy, and this dose was compared to the estimated lung absorbed dose calculated using an assumed 1 kg lung mass.

RESULTS

Patient-specific lung masses were significantly different from the generic 1 kg when compared individually for each patient (p < 0.0001). Median individualized lung mass was 0.71 (IQR: 0.59, 1.02) kg overall and was significantly different from the generic 1 kg lung mass for female patients [0.59 (0.50, 0.68) kg, (p < 0.0001)] but not for male patients [0.99 (0.71, 1.14) kg, (p = 0.24)]. Median estimated lung absorbed dose was 4.48 (2.38, 11.71) Gy using a patient-specific lung mass and 3.45 (1.81, 6.68) Gy when assuming a 1 kg lung mass for all patients. The estimated lung absorbed dose was significantly different using a patient-specific versus generic 1 kg lung mass when comparing the doses individually for each patient (p < 0.0001). The difference in the estimated lung absorbed dose between the patient-specific and generic 1 kg lung mass method was significant for female patients as a subgroup but not for male patients.

CONCLUSIONS

The current method of assuming a 1 kg lung mass for all patients inaccurately estimates the lung absorbed dose in ⁹⁰Y radioembolization therapy. Using patient-specific lung masses resulted in estimated lung absorbed doses that were significantly different from those calculated using an assumed 1 kg lung mass for all patients. A personalized dosimetry method that includes individualized lung masses is necessary and can warrant a ⁹⁰Y dose reduction in some patients with lung masses smaller than 1 kg.

LEVEL OF EVIDENCE

Level 3, Retrospective Study.

Yttrium-90 Selective Internal Radiation Therapy Plus Cryoablation for Recurrent Adrenocortical Carcinoma With Liver Metastases

Advanced adrenocortical carcinoma (ACC) has a poor prognosis and is often resistant to the conventional regimens of mitotane administration and systemic chemotherapy. In addition to surgery, local therapeutic measures can be valuable. Here, we present the case of a 33-year-old woman who developed left retroperitoneal local recurrent ACC with hepatic and pulmonary metastases 1 year after radical adrenalectomy. The tumors progressed under chemotherapy and mitotane treatments. She was treated with yttrium-90 selective internal radiation therapy (⁹⁰Y SIRT) for hepatic metastases and cryoablation of the local recurrent tumor, after which significant tumor shrinkage was observed. She then received radiofrequency ablation for the residual hepatic metastases and radiotherapy to the residual local recurrent tumor. Complete remission was achieved and maintained at least until the data cutoff day (15.8 months after the last treatment). This is the first published report of cryoablation in a patient with ACC and the third report of ⁹⁰Y SIRT use for hepatic metastasis of ACC. Cryoablation and ⁹⁰Y SIRT are local treatment choices for ACC that are worthy of further study.

Development of a scatter correction technique for planar 99mTc-MAA imaging to improve accuracy in lung shunt fraction estimation

PURPOSE

Prior to ⁹⁰Y selective internal radiation therapy (SIRT) treatment, ^99mTc-MAA scintigraphy imaging is used in the estimation of the lung shunt fraction (LSF). Planar imaging is recommended for determining a LSF ratio. However, the estimate may be affected by scatter contributions, attenuation and respiratory motion. The objective of this study was to correct for the effects of scatter in the LSF, towards the determination of a more accurate estimation method of LSF derived from planar scintigraphy imaging, which is recommended by international guidelines.

METHODS

The open access SIMIND Monte Carlo modelling software was used to estimate an optimum scatter window (SW) for scatter correction. The uncertainties associated with scatter and scatter contributions from the liver on the LSF were evaluated using an anthropomorphic thorax phantom and a virtual Vox-Man phantom. A brief retrospective examination of patient scans and tumour location investigated the impact that the inclusion of the simulated scatter corrections had on the LSF estimation.

RESULTS

The percentage overestimation of the manufacturer recommended method of LSF estimation was 192%. SW corrections improved the uncertainty to within 19% for the range of known LSFs. Similar findings were observed for our patient and tumour location studies.

CONCLUSION

The incorporated scatter corrections can significantly improve the accuracy of the LSF estimation, thereby providing a robust gamma camera, patient and tumour depth specific correction which is easily implementable. This is supported by Monte Carlo, phantom and preliminary patient studies.

Radioembolization, Principles and indications

Radioembolization is the selective application of radionuclide-loaded microspheres into liver arteries for the therapy of liver tumours and metastases. In this review, we focused on therapy planning and dosimetry, as well as the main indications of 90Y-glass and resin microspheres and 166Ho-microspheres.

Regional Therapy for Colorectal Cancer Liver Metastases: Which Modality and When?

For patients with unresectable colorectal liver metastases (uCRLM), regional therapies leverage the unique, dual blood supply to the liver; the hepatic artery is the main blood supply for liver tumors, whereas the portal vein supplies most normal hepatic parenchyma. Infusion of cancer therapies via the hepatic artery allows selective delivery to the tumors with relative sparing of normal liver tissue and little extrahepatic exposure, thus limiting systemic side effects. There is a paucity of randomized controlled trial evidence to inform the optimal integration of regional therapies into the management of CRLM. Hepatic arterial infusion pump (HAIP) chemotherapy has a potential survival benefit when used in the adjuvant setting after resection of CRLM. HAIP chemotherapy can be safely given with contemporary systemic therapies and is associated with a high objective response and rate of conversion to resectability in patients with uCRLM. Drug-eluting beads coated with irinotecan transarterial chemoembolization is associated with high objective response rates within the liver and has a well-established safety profile in patients with uCRLM. Transarterial radioembolization achieves high rates of response within the liver but is not associated with improvements in overall survival or quality of life in the first- or second-line setting for uCRLM. The best treatment approach is the one that most aligns with a given patients' values, preferences, and philosophy of care. In the first-line setting, HAIP could be offered to motivated patients who hope to achieve conversion to resectability. After progression on chemotherapy, HAIP, transarterial chemoembolization, and transarterial radioembolization are valuable treatment options to consider for patients with liver-limited or liver-predominant CRLM who seek to optimize response rates and regional control.

A novel tool for motion-related dose inaccuracies reduction in 99mTc-MAA SPECT/CT images for SIRT planning

INTRODUCTION

In Selective Internal Radiation Therapy (SIRT), ⁹⁰Y is administered to primary/secondary hepatic lesions. An accurate pre-treatment planning using ^99mTc-MAA SPECT/CT allows the assessment of its feasibility and of the activity to be injected. Unfortunately, SPECT/CT suffers from patient-specific respiratory motion which causes artifacts and absorbed dose inaccuracies. In this study, a data-driven solution was developed to correct the respiratory motion.

METHODS

The tool realigns the barycenter of SPECT projection images and shifts them to obtain a fine registration with the attenuation map. The tool was validated using a modified dynamic phantom with several breathing patterns. We compared the absorbed dose distributions derived from uncorrected(D_m)/corrected(D_c) images with static ones(D_s) in terms of γ-passing rates, 210 Gy isodose volumes, dose-volume histograms and percentage differences of mean doses (i.e., ΔD¯_m and ΔD¯_c, respectively). The tool was applied to twelve SIRT patients and the Bland-Altman analysis was performed on mean doses.

RESULTS

In the phantom study, the agreement between D_c and D_s was higher (γ-passing rates generally > 90%) than D_m and D_s. The isodose volumes in D_c were closer than D_m to D_s, with differences up to 10% and 30% respectively. A reduction from a median ΔD¯_m = -19.3% to ΔD¯_c = -0.9%, from ΔD¯_m = -42.8% to ΔD¯_c = -7.0% and from ΔD¯_m = 1586% to ΔD¯_c = 47.2% was observed in liver-, tumor- and lungs-like structures. The Bland-Altman analysis on patients showed variations (±50 Gy) and (±4 Gy) between D¯_c and D¯_m of tumor and lungs, respectively.

CONCLUSION

The proposed tool allowed the correction of ^99mTc-MAA SPECT/CT images, improving the accuracy of the absorbed dose distribution.

Precision dosimetry in yttrium-90 radioembolization through CT imaging of radiopaque microspheres in a rabbit liver model

PURPOSE

To perform precision dosimetry in yttrium-90 radioembolization through CT imaging of radiopaque microspheres in a rabbit liver model and to compare extracted dose metrics to those produced from conventional PET-based dosimetry.

MATERIALS AND METHODS

A CT calibration phantom was designed containing posts with nominal microsphere concentrations of 0.5 mg/mL, 5.0 mg/mL, and 25.0 mg/mL. The mean Hounsfield unit was extracted from the post volumes to generate a calibration curve to relate Hounsfield units to microsphere concentration. A nominal bolus of 40 mg of microspheres was administered to the livers of eight rabbits, followed by PET/CT imaging. A CT-based activity distribution was calculated through the application of the calibration curve to the CT liver volume. Post-treatment dosimetry was performed through the convolution of yttrium-90 dose-voxel kernels and the PET- and CT-based cumulated activity distributions. The mean dose to the liver in PET- and CT-based dose distributions was compared through linear regression, ANOVA, and Bland-Altman analysis.

RESULTS

A linear least-squares fit to the average Hounsfield unit and microsphere concentration data from the calibration phantom confirmed a strong correlation (r2 > 0.999) with a slope of 14.13 HU/mg/mL. A poor correlation was found between the mean dose derived from CT and PET (r2 = 0.374), while the ANOVA analysis revealed statistically significant differences (p < 10-12) between the MIRD-derived mean dose and the PET- and CT-derived mean dose. Bland-Altman analysis predicted an offset of 15.0 Gy between the mean dose in CT and PET. The dose within the liver was shown to be more heterogeneous in CT than in PET with an average coefficient of variation equal to 1.99 and 1.02, respectively.

CONCLUSION

The benefits of a CT-based approach to post-treatment dosimetry in yttrium-90 radioembolization include improved visualization of the dose distribution, reduced partial volume effects, a better representation of dose heterogeneity, and the mitigation of respiratory motion effects. Post-treatment CT imaging of radiopaque microspheres in yttrium-90 radioembolization provides the means to perform precision dosimetry and extract accurate dose metrics used to refine the understanding of the dose-response relationship, which could ultimately improve future patient outcomes.

Efficacy and Safety of Trans-Arterial Yttrium-90 Radioembolization in Patients with Unresectable Liver-Dominant Metastatic or Primary Hepatic Soft Tissue Sarcomas

Simple Summary

Sarcomas of the liver are a rare and aggressive group of malignancies for which surgery is the preferred treatment modality even though most patients are not surgical candidates and receive chemotherapy with poor outcomes. In these cases, trans-arterial liver-directed therapies are emerging as a new treatment option. Among these, radioembolization is a promising but understudied treatment option. In radioembolization, microbeads conjugated to a radioactive drug are injected into the blood vessels, nourishing the cancers and leading to cell death and tumor shrinkage. In this study, we retrospectively analyzed 35 patients with liver sarcomas receiving radioembolization at our institution. We found that those with disease control in the liver 6 months after the procedure had longer overall survival as well as patients with a liver progression-free interval post-procedure equal to or greater than 9 months. Patients with good performance status and normal liver function at baseline also had longer survival. The most common adverse reactions were nausea, fatigue, abdominal pain, and mild reversible abnormalities in liver function tests. Overall, our results suggest that radioembolization might be a safe and effective treatment option for patients with unresectable liver sarcomas.

Abstract

Patients with liver-dominant metastatic or primary hepatic soft tissue sarcomas (STS) have poor prognosis. Surgery can prolong survival, but most patients are not surgical candidates, and treatment response is limited with systemic chemotherapy. Liver-directed therapies have been increasingly employed in this setting, and Yttrium-90 trans-arterial radioembolization (TARE) is an understudied yet promising treatment option. This is a retrospective analysis of 35 patients with metastatic or primary hepatic STS who underwent TARE at a single institution between 2006 and 2020. The primary outcomes that were measured were overall survival (OS), liver progression-free survival (LPFS), and radiologic tumor response. Clinical and biochemical toxicities were assessed 3 months after the procedure. Median OS was 20 months (95% CI: 13.9–26.1 months), while median LPFS was 9 months (95% CI: 6.2–11.8 months). The objective response rate was 56.7%, and the disease control rate was 80.0% by mRECIST at 3 months. The following correlated with better OS post-TARE: liver disease control (DC) at 6 months (median OS: 40 vs. 17 months, p = 0.007); LPFS ≥ 9 months (median OS: 50 vs. 8 months, p < 0.0001); ECOG status 0–1 vs. 2 (median OS: 22 vs. 6 months, p = 0.042); CTP class A vs. B (median OS: 22 vs. 6 months, p = 0.018); and TACE post-progression (median OS: 99 vs. 16 months, p = 0.003). The absence of metastases at diagnosis was correlated with higher median LPFS (7 vs. 1 months, p = 0.036). Two grade 4 (5.7%) and ten grade 3 (28.6%) laboratory toxicities were identified at 3 months. There was one case of radioembolization-induced liver disease and two cases of radiation-induced peptic ulcer disease. We concluded that TARE could be an effective and safe treatment option for patients with metastatic or primary hepatic STS with good tumor response rates, low incidence of severe toxicity, and longer survival in patients with liver disease control post-TARE.

Pre- and post-treatment image-based dosimetry in90Y-microsphere radioembolization using the TOPAS Monte Carlo toolkit

Objective. To evaluate the pre-treatment and post-treatment imaging-based dosimetry of patients treated with 90Y-microspheres, including accurate estimations of dose to tumor, healthy liver and lung. To do so, the Monte Carlo (MC) TOPAS platform is in this work extended towards its utilization in radionuclide therapy.Approach. Five patients treated at the Massachusetts General Hospital were selected for this study. All patients had data for both pre-treatment SPECT-CT imaging using 99mTc-MAA as a surrogate of the 90Y-microspheres treatment and SPECT-CT imaging immediately after the 90Y activity administration. Pre- and post-treatment doses were computed with TOPAS using the SPECT images to localize the source positions and the CT images to account for tissue inhomoegeneities. We compared our results with analytical calculations following the voxel-based MIRD scheme.Main results. TOPAS results largely agreed with the MIRD-based calculations in soft tissue regions: the average difference in mean dose to the liver was 0.14 Gy GBq^-1(2.6%). However, dose distributions in the lung differed considerably: absolute differences in mean doses to the lung ranged from 1.2 to 6.3 Gy GBq^-1and relative differences from 153% to 231%. We also found large differences in the intra-hepatic dose distributions between pre- and post-treatment imaging, but only limited differences in the pulmonary dose.Significance. Doses to lung were found to be higher using TOPAS with respect to analytical calculations which may significantly underestimate dose to the lung, suggesting the use of MC methods for 90Y dosimetry. According to our results, pre-treatment imaging may still be representative of dose to lung in these treatments.

Theragnostics in primary and secondary liver tumors: the need for a personalized approach

Primary and secondary hepatic tumors have a dramatic impact in oncology. Despite many advances in diagnosis and therapy, the management of hepatic malignancies is still challenging, ranging from various loco-regional approaches to system therapies. In this scenario, theragnostic approaches, based on the administration of a radiopharmaceuticals' pair, the first labeled with a radionuclide suitable for the diagnostic phase and the second one bound to radionuclide emitting particles for therapy, is gaining more and more importance. Selective internal radiation therapy (SIRT) with microspheres labeled with ⁹⁰Y or ¹⁶⁶Ho is widely used as a loco-regional treatment for primary and secondary hepatic tumors. While ¹⁶⁶Ho presents both gamma and beta emission and can be therefore considered a real "theragnostic" agent, for ⁹⁰Y-microspheres theragnostic approach is realized at the diagnostic phase through the utilization of macroaggregates of human albumin, labeled with ^99mTc as "biosimilar" agent respect to microspheres. The aim of the present review was to cover theragnostic applications of ⁹⁰Y/¹⁶⁶Ho-labeled microspheres in clinical practice. Furthermore, we report the preliminary data concerning the potential role of some emerging theragnostic biomarkers for hepatocellular carcinoma, such as glypican-3 (GPC3) and prostate specific membrane antigen (PSMA).

Key Role of Personalized Dosimetry in Dose Adjustment for Selective Internal Radiotherapy: Retrospective Study of Patients Treated With 90Y Resin Microspheres

PURPOSE

Selective internal radiotherapy with 90Y microspheres is widely used for the treatment of patients with liver cancer. A dosimetric analysis using the dosimetry software Simplicit90y (Boston Scientific, Natick, MA) was conducted to define doses to the tumor and healthy liver, and to determine a threshold tumor dose that could predict progression-free survival.

METHODS

Patients experiencing hepatocellular carcinoma and treated with 90Y-labeled resin microspheres were included in a retrospective study. The time-to-progression of the target lesions (TTPLs) and overall survival (OS) were evaluated using Kaplan-Meier tests, and this comparison was based on a log-rank test.

RESULTS

Twenty-four procedures for patients with portal vein thrombosis were realized. Median follow-up was 16 months. A threshold tumor dose of 125 Gy was determined with a sensitivity of 89% and a specificity of 100%. For patients with a tumor dose of less than 125 Gy, the median OS was 7.5 months (95% confidence interval [CI], 5-14 months) and the TTPL was 3 months (95% CI, 2-6 months) versus 33 months (95% CI, 22-39 months) and 23 months (95% CI, 7-38 months), respectively, for those with a tumor dose of 125 Gy or more (P = 0.002 and P = 0.0004).

CONCLUSIONS

Personalized dosimetry based on 99mTc-MAA SPECT/CT is predictive of TTPL and OS in patients with hepatocellular carcinoma. Customized dosimetry software is essential to optimize treatment planning.

EANM dosimetry committee series on standard operational procedures: a unified methodology for 99mTc-MAA pre- and 90Y peri-therapy dosimetry in liver radioembolization with 90Y microspheres

The aim of this standard operational procedure is to standardize the methodology employed for the evaluation of pre- and post-treatment absorbed dose calculations in 90Y microsphere liver radioembolization. Basic assumptions include the permanent trapping of microspheres, the local energy deposition method for voxel dosimetry, and the patient-relative calibration method for activity quantification.The identity of 99mTc albumin macro-aggregates (MAA) and 90Y microsphere biodistribution is also assumed. The large observed discrepancies in some patients between 99mTc-MAA predictions and actual 90Y microsphere distributions for lesions is discussed. Absorbed dose predictions to whole non-tumoural liver are considered more reliable and the basic predictors of toxicity. Treatment planning based on mean absorbed dose delivered to the whole non-tumoural liver is advised, except in super-selective treatments.Given the potential mismatch between MAA simulation and actual therapy, absorbed doses should be calculated both pre- and post-therapy. Distinct evaluation between target tumours and non-tumoural tissue, including lungs in cases of lung shunt, are vital for proper optimization of therapy. Dosimetry should be performed first according to a mean absorbed dose approach, with an optional, but important, voxel level evaluation. Fully corrected 99mTc-MAA Single Photon Emission Computed Tomography (SPECT)/computed tomography (CT) and 90Y TOF PET/CT are regarded as optimal acquisition methodologies, but, for institutes where SPECT/CT is not available, non-attenuation corrected 99mTc-MAA SPECT may be used. This offers better planning quality than non dosimetric methods such as Body Surface Area (BSA) or mono-compartmental dosimetry. Quantitative 90Y bremsstrahlung SPECT can be used if dedicated correction methods are available.The proposed methodology is feasible with standard camera software and a spreadsheet. Available commercial or free software can help facilitate the process and improve calculation time.

Standardizing SPECT/CT dosimetry following radioembolization with yttrium-90 microspheres

Background

Multiple post-treatment dosimetry methods are currently under investigation for Yttrium-90 (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{90}\hbox {Y}$$\end{document}90Y) radioembolization. Within each methodology, a variety of dosimetric inputs exists that affect the final dose estimates. Understanding their effects is essential to facilitating proper dose analysis and crucial in the eventual standardization of radioembolization dosimetry. The purpose of this study is to investigate the dose differences due to different self-calibrations and mass density assignments in the non-compartmental and local deposition methods. A practical mean correction method was introduced that permits dosimetry in images where the quality is compromised by patient motion and partial volume effects.

Methods

Twenty-one patients underwent \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$^{90}\hbox {Y}$$\end{document}90Y radioembolization and were imaged with SPECT/CT. Five different self-calibrations (FOV, Body, OAR, Liverlung, and Liver) were implemented and dosimetrically compared. The non-compartmental and local deposition method were used to perform dosimetry based on either nominal- or CT calibration-based mass densities. A mean correction method was derived assuming homogeneous densities. Cumulative dose volume histograms, linear regressions, boxplots, and Bland Altman plots were utilized for analysis.

Results

Up to 270% weighted dose difference was found between self-calibrations with mean dose differences up to 50 Gy in the liver and 23 Gy in the lungs. Between the local deposition and non-compartmental methods, the liver and lung had dose differences within 0.71 Gy and 20 Gy, respectively. The local deposition method’s nominal and CT calibration-based mass density implementations dosimetric metrics were within 1.4% in the liver and 24% in the lungs. The mean lung doses calculated with the CT method were shown to be inflated. The mean correction method demonstrated that the corrected mean doses were greater by up to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim 5$$\end{document}∼5 Gy in the liver and lower by up to \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\sim 12$$\end{document}∼12 Gy in the lungs.

Conclusions

The OAR calibration may be utilized as a potentially more accurate and precise self-calibration. The non-compartmental method was found more comparable to the local deposition method in organs that were more homogeneous in mass densities. Due to the potential for inflated lung mean doses, the non-compartmental and local deposition method implemented with nominal mass densities is recommended for more consistent dosimetric results. If patient motion and partial volume effects are present in the liver, our practical correction method will calculate more representative doses in images suboptimal for dosimetry.

A deep-learning-based prediction model for the biodistribution of 90 Y microspheres in liver radioembolization

BACKGROUND

Radioembolization with ⁹⁰ Y microspheres is a treatment approach for liver cancer. Currently, employed dosimetric calculations exhibit low accuracy, lacking consideration of individual patient, and tissue characteristics.

PURPOSE

The purpose of the present study was to employ deep learning (DL) algorithms to differentiate patterns of pretreatment distribution of ^99m Tc-macroaggregated albumin on SPECT/CT and post-treatment distribution of ⁹⁰ Y microspheres on PET/CT and to accurately predict how the ⁹⁰ Y-microspheres will be distributed in the liver tissue by radioembolization therapy.

METHODS

Data for 19 patients with liver cancer (10 with hepatocellular carcinoma, 5 with intrahepatic cholangiocarcinoma, 4 with liver metastases) who underwent radioembolization with ⁹⁰ Y microspheres were used for the DL training. We developed a 3D voxel-based variation of the Pix2Pix model, which is a special type of conditional GANs designed to perform image-to-image translation. SPECT and CT scans along with the clinical target volume for each patient were used as inputs, as were their corresponding post-treatment PET scans. The real and predicted absorbed PET doses for the tumor and the whole liver area were compared. Our model was evaluated using the leave-one-out method, and the dose calculations were measured using a tissue-specific dose voxel kernel.

RESULTS

The comparison of the real and predicted PET/CT scans showed an average absorbed dose difference of 5.42% ± 19.31% and 0.44% ± 1.64% for the tumor and the liver area, respectively. The average absorbed dose differences were 7.98 ± 31.39 Gy and 0.03 ± 0.25 Gy for the tumor and the non-tumor liver parenchyma, respectively. Our model had a general tendency to underpredict the dosimetric results; the largest differences were noticed in one case, where the model underestimated the dose to the tumor area by 56.75% or 72.82 Gy.

CONCLUSIONS

The proposed deep-learning-based pretreatment planning method for liver radioembolization accurately predicted ⁹⁰ Y microsphere biodistribution. Its combination with a rapid and accurate 3D dosimetry method will render it clinically suitable and could improve patient-specific pretreatment planning.

Intercomparison of Geant4 low energy electromagnetic models in 90Y dosimetry

This work shows the comparison between Geant4 low energy electromagnetic physics lists G4EmLi-vermorePhysics, G4EmPenelopePhysics, G4EmLowEPPhysics, and G4EmDNAPhysics_option2 when simulating the energy deposition of low mono-energetic electrons and β^- emitted from ⁹⁰Y isotope. The simulation time and influence of production cut were considered. In the sense of balance between the accuracy and computer resource, G4EmPenelopePhysics can be proposed as the best physics model for our future Treatment Planning System (TPS) for treating liver cancer using ⁹⁰Y microsphere radioembolization therapy.

Conventional Hepatic Volumetry May Lead to Inaccurate Segmental Yttrium-90 Radiation Dosimetry

OBJECTIVE

To compare radioembolization treatment zone volumes from mapping cone beam CT (CBCT) versus planning CT/MRI and to model their impact on dosimetry.

METHODS

Y90 cases were retrospectively identified in which intra-procedural CBCT angiograms were performed. Segmental and lobar treatment zone volumes were calculated with semi-automated contouring using Couinaud venous anatomy (planning CT/MRI) or tumor angiosome enhancement (CBCT). Differences were compared with a Wilcoxon signed-rank test. Treatment zone-specific differences in segmental volumes by volumetric method were also calculated and used to model differences in delivered dose using medical internal radiation dosimetry (MIRD) at 200 and 120 Gy targets. Anatomic, pathologic, and technical factors likely affecting segmental volumes by volumetric method were evaluated.

RESULTS

Forty segmental and 48 lobar CBCT angiograms and corresponding planning CT/MRI scans were included. Median Couinaud- and CBCT-derived segmental volumes were 281 and 243 mL, respectively (p = 0.005). Differences between Couinaud and CBCT lobar volumes (right, left) were not significant (p = 0.24, p = 0.07). Couinaud overestimated segmental volumes in 28 cases by a median of 98 mL (83%) and underestimated in 12 cases by median 69 mL (20%). At a 200 Gy dose target, Couinaud estimates produced median delivered doses of 367 and 160 Gy in these 28 and 12 cases. At a 120 Gy target, Couinaud produced doses of 220 and 96 Gy. Proximal vs. distal microcatheter positioning, variant arterial anatomy, and tumor location on or near segmental watersheds were leading factors linked to volumetric differences.

CONCLUSION

Use of CBCT-based volumetry may allow more accurate, personalized dosimetry for segmental Y90 radioembolization.

Intra- inter-observer repeatability in liver computed tomography volumetry in patients undergoing radioembolization simulation

PURPOSE

The careful evaluation of MDCT is an essential step for the treatment planning in pre-treatment imaging work-up for Trans-Arterial Radio Embolization (TARE). It may provide unique volumetric data (CTVs), which are information useful for an effective and safe TARE. The purpose of this study is to demonstrate that the radiographer is able to calculate CTVs of TARE simulation with the same precision as the interventional radiologist.

METHODS

This study retrospectively considers 17 consecutive patients (8 males, 9 females; mean age 66.3 ± 13.2 years) who underwent pre-treatment work-up for TARE, between May 2019 and February 2020 (trial ID:2234 - protocol). For each patient, four specific parameters are evaluated from MDCT achieved during treatment simulation: healthy liver volume (HLV), the whole hepatic parenchyma (THV = healthy liver and TTV = tumour) involved by TARE, and whole liver volume (WLV). Four independent observers-R1 (expert interventional radiologist), T1, T2, and T3 (radiographers, with different experiences in the field of interventional radiology)-are involved in the imaging analysed.

RESULTS

All the 4 observers detected the same number of hepatic lesion(s) per patient. Regarding the three radiographers, the intra-observer reliability for CTVs is very high 0.997 to 1.000 (95%CI). Also inter-observer reproducibility between radiographers is excellent regarding CTVs, 0.965 to 0.999 (95%CI). The accuracy of radiographer evaluation is very high 0.964 to 0.999 (95%CI).

CONCLUSIONS AND IMPLICATIONS FOR PRACTICE

The high intra- and inter-observer reproducibility shows that a properly trained radiographers might have the same accuracy as interventional radiologists, in assessing liver CTV data for planning TARE.

Post-administration dosimetry in yttrium-90 radioembolization through micro-CT imaging of radiopaque microspheres in a porcine renal model

The purpose of this study is to perform post-administration dosimetry in yttrium-90 radioembolization through micro-CT imaging of radiopaque microsphere distributions in a porcine renal model and explore the impact of spatial resolution of an imaging system on the extraction of specific dose metrics. Following the administration of radiopaque microspheres to the kidney of a hybrid farm pig, the kidney was explanted and imaged with micro-CT. To produce an activity distribution, 400 MBq of yttrium-90 activity was distributed throughout segmented voxels of the embolized vasculature based on an established linear relationship between microsphere concentration and CT voxel value. This distribution was down-sampled to coarser isotropic grids ranging in voxel size from 2.5 to 15 mm to emulate nominal resolutions comparable to those found in yttrium-90 PET and Bremsstrahlung SPECT imaging. Dose distributions were calculated through the convolution of activity distributions with dose-voxel kernels generated using the GATE Monte Carlo toolkit. Contours were computed to represent normal tissue and target volumes. Dose-volume histograms, dose metrics, and dose profiles were compared to a ground truth dose distribution computed with GATE. The mean dose to the target for all studied voxel sizes was found to be within 5.7% of the ground truth mean dose.D70was shown to be strongly correlated with image voxel size of the dose distribution (r² = 0.90).D70is cited in the literature as an important dose metric and its dependence on voxel size suggests higher resolution dose distributions may provide new perspectives on dose-response relationships in yttrium-90 radioembolization. This study demonstrates that dose distributions with large voxels incorrectly homogenize the dose by attributing escalated doses to normal tissues and reduced doses in high-dose target regions. High-resolution micro-CT imaging of radiopaque microsphere distributions can provide increased confidence in characterizing the absorbed dose heterogeneity in yttrium-90 radioembolization.

Clinical Evaluation of a Three-Dimensional Internal Dosimetry Technique for Liver Radioembolization with 90Y Microspheres Using Dose Voxel Kernels

Background: The purpose of this study was to develop a rapid, reliable, and efficient tool for three-dimensional (3D) dosimetry treatment planning and post-treatment evaluation of liver radioembolization with ⁹⁰Y microspheres, using tissue-specific dose voxel kernels (DVKs) that can be used in everyday clinical practice. Materials and Methods: Two tissue-specific DVKs for ⁹⁰Y were calculated through Monte Carlo (MC) simulations. DVKs for the liver and lungs were generated, and the dose distribution was compared with direct MC simulations. A method was developed to produce a 3D dose map by convolving the calculated DVKs with the activity biodistribution derived from clinical single-photon emission computed tomography (SPECT) or positron emission tomography (PET) images. Image registration for the SPECT or PET images with the corresponding computed tomography scans was performed before dosimetry calculation. The authors first compared the DVK convolution dosimetry with a direct full MC simulation on an XCAT anthropomorphic phantom. They then tested it in 25 individual clinical cases of patients who underwent ⁹⁰Y therapy. All MC simulations were carried out using the GATE MC toolkit. Results: Comparison of the measured absorbed dose using tissue-specific DVKs and direct MC simulation on 25 patients revealed a mean difference of 1.07% ± 1.43% for the liver and 1.03% ± 1.21% for the tumor tissue, respectively. The largest difference between DVK convolution and full MC dosimetry was observed for the lung tissue (10.16% ± 1.20%). The DVK statistical uncertainty was <0.75% for both media. Conclusions: This semiautomatic algorithm is capable of performing rapid, accurate, and efficient 3D dosimetry. The proposed method considers tissue and activity heterogeneity using tissue-specific DVKs. Furthermore, this method provides results in <1 min, making it suitable for everyday clinical practice.

Tumor-to-Normal Ratio Relationship between Planning Technetium-99 Macroaggregated Albumin and Posttherapy Yttrium-90 Bremsstrahlung SPECT/CT

PURPOSE

To quantify the relationship of the tumor-to-normal ratio (TNR) attained from the technetium-99m macroaggregated albumin (MAA) and posttreatment yttrium-90 bremsstrahlung (Y90-Brem) single-photon emission computerized tomography (SPECT)/computer tomography (CT) studies in patients with hepatocellular carcinoma (HCC) treated with glass microspheres.

MATERIALS AND METHODS

Retrospectively, a total of 190 consecutive patients with HCC who underwent 204 MAA and Y90-Brem SPECT/CT for glass microsphere Y90 radiation segmentectomy (Y90-RS) or lobar treatment (Y90-RLT) between 2013 and 2018 were included. Semi-automated regions-of-interests were drawn around the targeted tumor and nontumoral liver tissue on the SPECT/CT studies. TNR values from MAA and Y90-Brem SPECT/CT were compared using paired t-tests, Pearson correlation, and median with interquartile ranges (IQR).

RESULTS

The mean TNR for MAA and Y90-Brem SPECT/CT was 2.96 ± 1.86 (median, 2.64; IQR, 2.50) and 2.29 ± 1.10 (median, 2.06; IQR, 1.05), respectively (P < .0001). The mean Y90-RLT TNR was 2.88 ± 1.67 (median, 2.59; IQR, 0.83) and 2.17 ± 0.89 (median, 1.98; IQR, 0.81) for MAA and Y90-Brem SPECT/CT, respectively (P < .0001). The mean Y90-RS TNR was 3.02 ± 2.01 (median, 2.87; IQR, 3.01) and 2.39 ± 1.25 (median, 2.11; IQR, 1.28) for MAA and Y90-Brem SPECT/CT, respectively (P = .0003). TNR attained from MAA and Y90 SPECT/CT studies showed a moderate correlation in a positive linear fashion for the overall (r = 0.54; P < .001), Y90-RLT (r = 0.66, P < .001), and Y90-RS cohorts (r = 0.48, P < .001).

CONCLUSIONS

The TNR attained from Y90-Brem SPECT/CT is often underestimated, positively correlated, and less variable than that attained from MAA SPECT/CT.