Partition model for estimating radiation doses from yttrium-90 microspheres in treating hepatic tumours

Voxel-Based Dosimetry as a Means for Treatment Personalisation in Radioembolization: A Systematic Review

INTRODUCTION

Radionuclide therapy including 90Y radioembolization is an established form of brachytherapy for treatment of malignancy including hepatocellular carcinoma. Currently, there are several methods available to estimate patient absorbed dose, including voxel-based dosimetry, that can achieve a level of personalisation in the planning and outcome assessments of radioembolization. Despite the advantages of voxel-based dosimetry, it remains a relatively new concept in radioembolization. This study evaluates if voxel-based dosimetry was associated with improved treatment efficacy in radioembolization planning.

METHODS

A systematic review was conducted by searching relevant databases (Medline Ovid, PubMed, Embase Ovid, CINAHL Complete, Cochrane Library, CENTRAL, Australian New Zealand Clinical Trials Registry, ClinicalTrials.gov, WHO International Trials Registry, Google Scholar) for literature regarding voxel-based dosimetry in radioembolization.

RESULTS

A total of 41 papers were included for this systematic review. Review of these studies revealed that voxel-based dosimetry can benefit numerous aspects of radioembolization in radionuclide therapy including predicting tumour response, toxicity and patient survival. Numerous studies also indicated that voxel-based dosimetry in radioembolization is a more accurate approach in establishing a dose-effect relationship in targeted radionuclide therapy when compared to other methods. Despite these promising findings, these studies did not investigate or comment on the accuracy of voxel-based dosimetry.

CONCLUSION

The evidence from this review highlights that voxel-based dosimetry can improve treatment efficacy in radioembolization planning. However, further studies are required to validate the accuracy and feasibility of voxel-based dosimetry in clinical practice.

Predicting treatment responses using magnetic resonance imaging-based radiomics in hepatocellular carcinoma patients undergoing transarterial radioembolization

OBJECTIVE

This study evaluates the efficacy of magnetic resonance imaging-based radiomics in predicting treatment responses in hepatocellular carcinoma patients undergoing transarterial radioembolization.

METHODS

Pre-treatment magnetic resonance imaging scans from 65 hepatocellular carcinoma patients were analyzed. Radiomic features were extracted from axial T1-weighted and T2-weighted sequences using a standardized workflow involving image preprocessing, segmentation, and feature extraction. Multivariate logistic regression models combining radiomic and clinical features were developed to predict treatment outcomes. The performance of the models was evaluated using the area under the curve metric.

RESULTS

The study included 65 patients with a median age of 64 years; 44.6% showed a complete response, while 55.4% showed a non-complete response. The median radiomics score in the T1-weighted portal phase was -0.49 for non-complete responders and -0.07 for complete responders (p<0.001). In the T2-weighted sequence, the median radiomics score was -0.76 for non-complete responders and 1.1 for complete responders (p<0.001). Tumor size ≥5 cm was a significant predictor of non-complete response in univariate analysis (p=0.027) but not in multivariate analysis after adding radiomics scores. The area under the curve for the radiomics signature in predicting non-complete response was 0.754 for T1-weighted and 0.850 for T2-weighted sequences.

CONCLUSION

Magnetic resonance imaging-based radiomics enhances the prediction of treatment responses in hepatocellular carcinoma patients undergoing transarterial radioembolization. Integrating radiomic features with clinical parameters significantly improves predictive accuracy.

A comparison of methods for in vivo activity and absorbed dose quantification with PET/CT following yttrium-90 radioembolization

BACKGROUND

Yttrium-90 (90Y) positron emission tomography (PET)/computed tomography (CT) imaging is increasingly being used to perform tumor (T) and normal liver (NL) voxel dosimetry after 90Y-radioembolization (90Y-RE). Yet, the accuracy of in vivo 90Y-PET/CT imaging, subject to motion blur and co-registration inaccuracies, and 90Y-PET/CT dose quantification, subject to availability of different voxel dosimetry algorithms, are not well understood.

PURPOSE

The purpose of this study was to investigate the accuracy of 90Y-PET/CT-based activity estimates following 90Y-RE and characterize differences between 90Y-PET/CT-based voxel dosimetry algorithms.

METHODS

Thirty-five patients underwent 90Y-PET/CT imaging after 90Y-RE with TheraSphere. The net administered 90Y activity (Aadmin) was determined using a dose calibrator and pre- and post-procedure exposure rate measurements. The summation of image-based activity (Aimage) was extracted from perfused volume (PV) and 3D-isotropically 2-cm expanded PV contour (PV+2 cm). Absorbed doses were calculated using voxel S-value (VSV), local deposition method (LDM), and LDM with known activity (LDMKA) dosimetry algorithms. Linear regression and Bland-Altman analysis quantified the relationship between Aimage and Aadmin and between mean dose estimates (DLDM, DVSV, DLDM-KA) for PV, T, and perfused NL volumes.

RESULTS

While Aadmin and Aimage in PV were highly correlated (R2 > 0.95), the mean bias ± standard error (SE) and (95% limits of agreement, LOA) was significantly non-zero with -22.7 ± 4.7% (± 28.4%). In PV+2 cm, the mean bias ± SE (± LOA) decreased to 1.3 ± 3.4% (± 18.0%) consistent with zero mean error. DLDM and DVSV were highly correlated (R2 > 0.99) for all volumes of interest (VOIs) and the mean bias ± SE (± LOA) was 2.2 ± 0.2% (± 1.0%), 0.7 ± 0.4% (± 2.8%), and 3.2 ± 0.5% (± 2.8%) for PV, T, and NL, respectively. DLDM-KA and DVSV were correlated with R2 = 0.86, 0.80, and 0.86 for PV, T, and NL, respectively. The mean bias ± SE (± LOA) between DLDM-KA and DVSV was significantly non-zero with -19.6 ± 5.1% (± 31.0%), -20.8 ± 4.4% (± 29.0%), and -18.1 ± 5.3% (± 31.1%) for PV, T, and NL, respectively.

CONCLUSIONS

The summation of Aimage in PV was underestimated relative to Aadmin. Only by accounting for respiratory motion, limited spatial resolution, and PET/CT co-registration errors through VOI expansion was Aimage, on average, equal to Aadmin. The differences between DLDM and DVSV were not clinically relevant, though DLDM-KA was approximately 20% greater than DVSV. Given the high quantitative accuracy of dose calibrators and challenges associated with accurate 90Y-PET/CT quantification, LDMKA is the preferred algorithm for accurate 90Y-PET/CT-based dosimetry following 90Y-RE.

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.

Use of dose-volume histograms for metabolic response prediction in hepatocellular carcinoma patients undergoing transarterial radioembolization with Y-90 resin microspheres

INTRODUCTION

Voxel-based dosimetry offers improved outcomes in the treatment of hepatocellular carcinoma (HCC) with transarterial radioembolization (TARE) using glass microspheres. However, the adaptation of voxel-based dosimetry to resin-based microspheres has been poorly studied, and the prognostic relevance of heterogeneous dose distribution remains unclear. This study aims to explore the use of dose-volume histograms for resin microspheres and to determine thresholds for objective metabolic response in HCC patients treated with resin-based TARE.

METHODS

We retrospectively reviewed HCC patients who underwent TARE with Y-90-loaded resin microspheres in our institution between January 2021 and December 2022. Voxel-based dosimetry was performed on post-treatment Y-90 PET/CT images to extract parameters including mean dose absorbed by the tumor (mTD), the percentage of the targeted tumor volume (pTV), and the minimum doses absorbed by consecutive percentages within the tumor volume (D10, D25, D50, D75, D90). Assessment of metabolic response was done according to PERCIST criteria with F-18 FDG PET/CT imaging at 8-12 weeks after the treatment.

RESULTS

This study included 35 lesions targeted with 22 TARE sessions in 19 patients (15 males, 4 females, mean age 60 ± 13 years). Objective metabolic response was achieved in 43% of the lesions (n = 15). Responsive lesions had significantly higher mTD, pTV, and D25-D90 values (all p < 0.05). Optimal cut-off values for mTD, pTV, and D50 were 94.6 Gy (sensitivity 73%, specificity 70%, AUC 0.72), 94% (sensitivity 73%, specificity 55%, AUC 0.64), and 91 Gy (sensitivity 80%, specificity 80%, AUC 0.80), respectively.

CONCLUSION

Parameters derived from dose-volume histograms could offer valuable insights for predicting objective metabolic response in HCC patients treated with resin-based TARE. If verified with larger prospective cohorts, these parameters could enhance the precision of dose distribution and potentially optimize treatment outcomes.

A microscopic model of the dose distribution in hepatocellular carcinoma after selective internal radiation therapy

The dosimetry evaluation for the selective internal radiation therapy is currently performed assuming a uniform activity distribution, which is in contrast with literature findings. A 2D microscopic model of the perfused liver was developed to evaluate the effect of two different 90Y microspheres distributions: i) homogeneous partitioning with the microspheres equally distributed in the perfused liver, and ii) tumor-clustered partitioning where the microspheres distribution is inferred from the patient specific images.

METHODS

Two subjects diagnosed with liver cancer were included in this study. For each subject, abdominal CT scans acquired prior to the SIRT and post-treatment 90Y positron emission tomography were considered. Two microspheres partitionings were simulated namely homogeneous and tumor-clustered partitioning. The homogeneous and tumor-clustered partitionings were derived starting from CT images. The microspheres radiation is simulated by means of Russell's law.

RESULTS

In homogenous simulations, the dose delivery is uniform in the whole liver while in the tumor-clustered simulations a heterogeneous distribution of the delivered dose is visible with higher values in the tumor regions. In addition, in the tumor-clustered simulation, the delivered dose is higher in the viable tumor than in the necrotic tumor, for all patients. In the tumor-clustered case, the dose delivered in the non-tumoral tissue (NTT) was considerably lower than in the perfused liver.

CONCLUSIONS

The model proposed here represents a proof-of-concept for personalized dosimetry assessment based on preoperative CT images.

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.

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.

Predictive Dosimetry and Outcomes of Hepatocellular Carcinoma Treated by Yttrium-90 Resin Microsphere Radioembolization: A Retrospective Analysis Using Technetium-99m Macroaggregated Albumin Single Photon Emission CT/CT and Planning Software

PURPOSE

To characterize estimated mean absorbed tumor dose (ADT), objective response (OR), and estimated target dose of hepatocellular carcinoma (HCC) after resin microsphere yttrium-90 (90Y) radioembolization using partition dosimetry.

MATERIALS AND METHODS

In this retrospective, single-center study, multicompartment dosimetry of index tumors receiving 90Y radioembolization between October 2015 and June 2022 was performed using a commercial software package and pretreatment technetium-99m macroaggregated albumin single photon emission computed tomography (SPECT)/computed tomography (CT). In total, 101 patients with HCC underwent 102 treatments of 127 index tumors. Patients underwent imaging every 2-3 months after treatment to determine best response per modified Response Evaluation Criteria in Solid Tumors (mRECIST). Best response was defined as the greatest response category per mRECIST and categorized as OR or nonresponse (NR). A Cox proportional hazards model evaluated the probability of tumor OR and progression-free survival using ADT.

RESULTS

The median follow-up period was 148 days (interquartile range [IQR], 92-273 days). The median ADT of OR was 141.9 Gy (IQR, 89.4-215.8 Gy) compared with the median ADT of NR treatments of 70.8 Gy (IQR, 42.0-135.3 Gy; P < .001). Only ADT was predictive of response (hazard ratio = 2.79 [95% confidence interval {CI}: 1.44-5.40]; P = .003). At 6 months, an ADT of 157 Gy predicted 90.0% (95% CI: 41.3%-98.3%) probability of OR. At 1 year, an ADT of 157 Gy predicted 91.6% (95% CI: 78.3%-100%) probability of progression-free survival. Partition modeling and delivered activity were predictive of progression (P = .021 and P = .003, respectively).

CONCLUSIONS

For HCC treated with resin microspheres, tumors receiving higher ADT exhibited higher rates of OR. An ADT of 157 Gy predicted 90.0% OR at 6 months.

Liver Tumor Enhancement at Hybrid Angio-CT and Comparison With Tumor and Hepatic Parenchymal Distribution of Yttrium-90 Microspheres by Positron Emission Tomography

This single-center retrospective study evaluated patients who underwent treatment of a primary or secondary hepatic malignancy with injection of glass or resin yttrium-90 (90Y) microspheres with a corresponding hybrid angiography-computed tomography (angio-CT) and 90Y positron emission tomography (PET). Volumetric contours were defined by three independent observers and were used to calculate relative tumoral enhancement at angio-CT. This parameter was compared with the tumor-to-normal (T/N) activity ratio predicted by technetium-99m macro-aggregated albumin (99mTc-MAA) single photon emission computed tomography (SPECT) and microsphere activity distribution by 90Y PET. A similar correlation was observed for the enhancement ratio at angio-CT with observed microsphere distribution at 90Y PET (r=0.34) to that predicted by 99mTc-MAA SPECT (r=0.32). The enhancement ratio on angio-CT performed as well as 99mTc-MAA in the prediction of 90Y PET activity distribution. The technique could not be readily applied to tumors with large areas of hypoattenuation (necrosis) on angio-CT. With refinement and further study, this technique could be used as a quantitative adjunct to standard-of-care 99mTc-MAA SPECT for dosimetry calculations and prediction of microsphere distribution to maximize tumor response and minimize hepatotoxicity.

Optimization of Y-90 Radioembolization Imaging for Post-Treatment Dosimetry on a Long Axial Field-of-View PET/CT Scanner

BACKGROUND

PET imaging after yttrium-90 (Y-90) radioembolization is challenging because of the low positron fraction of Y-90 (32 × 10-6). The resulting low number of events can be compensated by the high sensitivity of long axial field-of-view (LAFOV) PET/CT scanners. Nevertheless, the reduced event statistics require optimization of the imaging protocol to achieve high image quality (IQ) and quantification accuracy sufficient for post-treatment dosimetry.

METHODS

Two phantoms (NEMA IEC and AbdoMan phantoms, mimicking human liver) filled with Y-90 and a 4:1 sphere (tumor)-to-background ratio were scanned for 24 h with the Biograph Vision Quadra (Siemens Healthineers). Eight patients were scanned after Y-90 radioembolization (1.3-4.7 GBq) using the optimized protocol (obtained by phantom studies). The IQ, contrast recovery coefficients (CRCs) and noise were evaluated for their limited and full acceptance angles, different rebinned scan durations, numbers of iterations and post-reconstruction filters. The s-value-based absorbed doses were calculated to assess their suitability for dosimetry.

RESULTS

The phantom studies demonstrate that two iterations, five subsets and a 4 mm Gaussian filter provide a reasonable compromise between a high CRC and low noise. For a 20 min scan duration, an adequate CRC of 56% (vs. 24 h: 62%, 20 mm sphere) was obtained, and the noise was reduced by a factor of 1.4, from 40% to 29%, using the full acceptance angle. The patient scan results were consistent with those from the phantom studies, and the impacts on the absorbed doses were negligible for all of the studied parameter sets, as the maximum percentage difference was -3.89%.

CONCLUSIONS

With 2i5s, a 4 mm filter and a scan duration of 20 min, IQ and quantification accuracy that are suitable for post-treatment dosimetry of Y-90 radioembolization can be achieved.

Predicting the net administered activity in 90 Y-radioembolization patients from post-procedure 90 Y-SPECT/CT

BACKGROUND

The calculation of the net administered activity (Aadmin ) in patients undergoing 90 Y-radioembolization is essential for dosimetry and radiation safety, yet current methods for measuring residual 90 Y activity are often associated with high uncertainty. Therefore, an accurate, robust, and clinically viable method for the determination of Aadmin across approved 90 Y microsphere devices is desirable.

PURPOSE

We report on a novel method to determine Aadmin by leveraging the quantitative capabilities of SPECT/CT to measure 90 Y-emission in vivo from patients following 90 Y-radioembolization with glass or resin microspheres.

METHODS

90 Y-SPECT/CT attenuation-corrected count data from 147 sequential 90 Y-radioembolization patients was used for this analysis. Aadmin was calculated as part of routine clinical practice via the exposure rate differences between the initial 90 Y-vial and the 90 Y-residual jar. This served as our gold standard measure of Aadmin . Patient data for each microsphere device were separated into training and testing cohorts to first develop regression models and then to independently assess model performance. The training cohorts were divided into four groups: first, based on the microsphere device (glass or resin), and second, based on the SPECT volume used to calculate counts (the full SPECT field of view (FOV) or liver only (VOIliver )). Univariate linear regression models were generated for each group to predict Aadmin based on 90 Y-SPECT data from the training cohorts. Leave-one-out cross validation was implemented to estimate variability in model parameters. To assess performance, linear models derived from the training cohort were applied to 90 Y-SPECT data from the testing cohort. A comparison of the models between microspheres devices was also performed.

RESULTS

Linear models derived from the glass and resin training cohorts demonstrated a strong, positive correlation between 90 Y-SPECT image counts and Aadmin for VOIliver and FOV with R2  > 0.98 in all cases. In the glass training cohort, model accuracy (100%-absolute mean prediction error) and precision (95% prediction intervals of mean prediction error) were 99.0% and 15.4% for the VOIliver and 99.7% and 17.5% for the FOV models, respectively. In the resin training cohort, the corresponding values were 98.6% and 16.7% for VOIliver and > 99.9% and 11.4% for the FOV models, respectively. The application of these linear models to 90 Y-SPECT data from the testing cohort showed Aadmin prediction errors to have high accuracy and precision for both microsphere devices. For the glass testing cohort, accuracy (precision) was 96.9% (19.6%) and 98.8% (21.1%) for the VOIliver and FOV models, respectively. The corresponding values for the resin training cohort were 97.3% (26.2%) and 98.5% (25.7%) for the VOIliver and FOV models, respectively. The slope of the linear models between the two microsphere devices was observed to be significantly different with resin microspheres generating 48%-49% more SPECT counts for equivalent 90 Y activity based on each device manufacturer's activity calibration process.

CONCLUSION

90 Y-SPECT image counts can reliably predict (accuracy > 95% and precision < 18%) Aadmin after 90 Y-radioembolization, with performance characteristics essentially equivalent for both glass and resin microspheres. There is a clear indication that activity calibrations are fundamentally different between the two microsphere devices.

Pre-treatment dosimetry in90Y-SIRT: Is it possible to optimise SPECT reconstruction parameters and calculation methods for accurate dosimetry?

PURPOSE

The aim of this study was (a) to optimise the99mTc-SPECT reconstruction parameters for the pre-treatment dosimetry of90Y-selective internal radiation therapy (SIRT) and (b) to compare the accuracy of clinical dosimetry methods with full Monte-Carlo dosimetry (fMCD) performed with Gate.

METHODS

To optimise the reconstruction parameters, two hundred reconstructions with different parameters were performed on a NEMA phantom, varying the number of iterations, subsets, and post-filtering. The accuracy of the dosimetric methods was then investigated using an anthropomorphic phantom. Absorbed dose maps were generated using (1) the Partition Model (PM), (2) the Dose Voxel Kernel (DVK) convolution, and (3) the Local Deposition Method (LDM) with known activity restricted to the whole phantom (WP) or to the liver and lungs (LL). The dose to the lungs was calculated using the "multiple DVK" and "multiple LDM" methods.

RESULTS

Optimal OSEM reconstruction parameters were found to depend on object size and dosimetric criterion chosen (Dmean or DVH-derived metric). The Dmean of all three dosimetric methods was close (≤ 10%) to the Dmean of fMCD simulations when considering large segmented volumes (whole liver, normal liver). In contrast, the Dmean to the small volume (∅=31) was systemically underestimated (12%-25%). For lungs, the "multiple DVK" and "multiple LDM" methods yielded a Dmean within 20% for the WP method and within 10% for the LL method.

CONCLUSIONS

All three methods showed a substantial degradation of the dose-volume histograms (DVHs) compared to fMCD simulations. The DVK and LDM methods performed almost equally well, with the "multiple DVK" method being more accurate in the lungs.

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.

Predictive Value of [99mTc]-MAA-Based Dosimetry in Hepatocellular Carcinoma Patients Treated with [90Y]-TARE: A Single-Center Experience

Transarterial radioembolization is a well-established method for the treatment of hepatocellular carcinoma. The tolerability and incidence of hepatic decompensation are related to the doses delivered to the tumor and healthy liver. This retrospective study was performed at our center to evaluate whether tumor- and healthy-liver-absorbed dose levels in TARE are predictive of tumor response according to the mRECIST 1.1 criteria and overall survival. One hundred and six patients with hepatocellular carcinoma were treated with [⁹⁰Y]-loaded resin microspheres and completed the follow-up. The dose delivered to each compartment was calculated using a compartmental model. The model was based on [^99mTc]-labelled albumin aggregate images obtained before the start of therapy. Tumor response was assessed after three months of treatment. Kaplan-Meier analysis was used to assess survival. The mean age of our population was 66 ± 13 years with a majority being BCLC B tumors. Forty-two patients presented with portal vein thrombosis. The response rate was 57% in the overall population and 59% in patients with thrombosis. Target-to-background (TBR) values measured on initial [^99mTc]MAA-SPECT-imaging and tumor model dosimetric values were associated with tumor response (p < 0.001 and p = 0.009, respectively). A dosimetric threshold of 136.5 Gy was predictive of tumor response with a sensitivity of 84.2% and specificity of 89.4%. Overall survival was 24.1 months [IQR 13.1-36.4] for patients who responded to treatment compared to 10.4 months [IQR 6.3-15.9] for the remaining patients (p = 0.022). In this cohort, the initial [^99mTc]MAA imaging is predictive of response and survival. The dosimetry prior to the application of TARE can be used for treatment planning and our results also suggest that the therapy is well-tolerated. In particular, hepatic decompensation can be predicted even in the presence of PVT.

SPECT and CT misregistration reduction in [99mTc]Tc-MAA SPECT/CT for precision liver radioembolization treatment planning

PURPOSE

Respiration and body movement induce misregistration between static [99mTc]Tc-MAA SPECT and CT, causing lung shunting fraction (LSF) and tumor-to-normal liver ratio (TNR) errors for 90Y radioembolization planning. We aim to alleviate the misregistration between [99mTc]Tc-MAA SPECT and CT using two registration schemes on simulation and clinical data.

METHODS

In the simulation study, 70 XCAT phantoms were modeled. The SIMIND Monte Carlo program and OS-EM algorithm were used for projection generation and reconstruction, respectively. Low-dose CT (LDCT) at end-inspiration was simulated for attenuation correction (AC), lungs and liver segmentation, while contrast-enhanced CT (CECT) was simulated for tumor and perfused liver segmentation. In the clinical study, 16 patient data including [99mTc]Tc-MAA SPECT/LDCT and CECT with observed SPECT and CT mismatch were analyzed. Two liver-based registration schemes were studied: SPECT registered to LDCT/CECT and vice versa. Mean count density (MCD) of different volumes-of-interest (VOIs), normalized mutual information (NMI), LSF, TNR, and maximum injected activity (MIA) based on the partition model before and after registration were compared. Wilcoxon signed-rank test was performed.

RESULTS

In the simulation study, compared to before registration, registrations significantly reduced estimation errors of MCD of all VOIs, LSF (Scheme 1: - 100.28%, Scheme 2: - 101.59%), and TNR (Scheme 1: - 7.00%, Scheme 2: - 5.67%), as well as MIA (Scheme 1: - 3.22%, Scheme 2: - 2.40%). In the clinical study, Scheme 1 reduced 33.68% LSF and increased 14.75% TNR, while Scheme 2 reduced 38.88% LSF and increased 6.28% TNR compared to before registration. One patient may change from 90Y radioembolization untreatable to treatable and other patients may change the MIA up to 25% after registration. NMI between SPECT and CT was significantly increased after registrations in both studies.

CONCLUSION

Registration between static [99mTc]Tc-MAA SPECT and corresponding CTs is feasible to reduce their spatial mismatch and improve dosimetric estimation. The improvement of LSF is larger than TNR. Our method can potentially improve patient selection and personalized treatment planning for liver 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.

Voxel-S-Value based 3D treatment planning methods for Y-90 microspheres radioembolization based on Tc-99m-macroaggregated albumin SPECT/CT

Partition model (PM) for Y-90 microsphere radioembolization is limited in providing 3D dosimetrics. Voxel-S-Values (VSV) method has good agreement with Monte Carlo (MC) simulations for 3D absorbed dose conversion. We propose a new VSV method and compare its performance along with PM, MC and other VSV methods for Y-90 RE treatment planning based on Tc-99m MAA SPECT/CT. Twenty Tc-99m-MAA SPECT/CT patient data are retrospectively analyzed. Seven VSV methods are implemented: (1) local energy deposition; (2) liver kernel; (3) liver kernel and lung kernel; (4) liver kernel with density correction (LiKD); (5) liver kernel with center voxel scaling (LiCK); (6) liver kernel and lung kernel with density correction (LiLuKD); (7) proposed liver kernel with center voxel scaling and lung kernel with density correction (LiCKLuKD). Mean absorbed dose and maximum injected activity (MIA) obtained by PM and VSV are evaluated against MC results, and 3D dosimetrics generated by VSV are compared with MC. LiKD, LiCK, LiLuKD and LiCKLuKD have the smallest deviation in normal liver and tumors. LiLuKD and LiCKLuKD have the best performance in lungs. MIAs are similar by all methods. LiCKLuKD could provide MIA consistent with PM, and precise 3D dosimetrics for Y-90 RE treatment planning.

Comparison of Bolus Versus Dual-Syringe Administration Systems on Glass Yttrium-90 Microsphere Deposition in an In Vitro Microvascular Hepatic Tumor Model

PURPOSE

To utilize an in vitro microvascular hepatic tumor model to compare the deposition characteristics of glass yttrium-90 microspheres using the dual-syringe (DS) and traditional bolus administration methods.

MATERIALS AND METHODS

The microvascular tumor model represented a 3.5-cm tumor in a 1,400-cm³ liver with a total hepatic flow of 160 mL/min and was dynamically perfused. A microcatheter was placed in a 2-mm artery feeding the tumor model and 2 additional nontarget arteries. Glass microspheres with a diameter of 20-30 μm were administered using 2 methods: (a) DS delivery at a concentration of 50 mg/mL in either a single, continuous 2-mL infusion or two 1-mL infusions and (b) bolus delivery (BD) of 100 mg of microspheres in a single 3-mL infusion.

RESULTS

Overall, the degree of on-target deposition of the microspheres was 85% ± 11%, with no significant differences between the administration methods. Although the distal penetration into the tumor arterioles was approximately 15 mm (from the second microvascular bifurcation of the tumor model) for all the cases, the distal peak particle counts were significantly higher for the DS delivery case (approximately 5 × 10⁵ microspheres achieving distal deposition vs 2 × 10⁵ for the BD case). This resulted in significantly higher deposition uniformity within the tumor model (90% for the DS delivery case vs 80% for the BD case, α = 0.05).

CONCLUSIONS

The use of this new in vitro microvascular hepatic tumor model demonstrated that the administration method can affect the deposition of yttrium-90 microspheres within a tumor, with greater distal deposition and more uniform tumor coverage when the microspheres are delivered at consistent concentrations using a DS delivery device. The BD administration method was associated with less favorable deposition characteristics of the microspheres.

Radioembolization in patients with hepatocellular carcinoma: a series of 53 cases

OBJECTIVE

To contribute our results to increase the scientific evidence about the use of radioembolization in the management of patients with hepatocellular carcinoma.

MATERIAL AND METHODS

This retrospective review included 53 patients with hepatocellular carcinoma treated with radioembolization at our center. Patients were classified according to the BCLC algorithm in detail according to their Child-Pugh functional status. We analyzed survival using the Kaplan-Meier method. We used Cox regression analysis to determine clinically significant parameters, including the doses administered in the parameters studied.

RESULTS

Patients ranged in age from 28 to 86 years (mean, 60 years). A total of 61 procedures were done. The mean activity administered was 2.8GBq (0.7-6.4GBq), with a mean dose of 229.9Gy (74-425.9Gy) administered in the tumor. Progression-free survival was 6.7 months and overall survival was 12.8 months. Differences in disease-free survival according to BCLC and Child-Pugh classification were not significant (p=0.848 and p=0.252, respectively). The clinical parameters that were significantly different with respect to overall survival were bilirubin levels (p<0.001), pretreatment transaminase levels (AST) (p=0.022), Child-Pugh subclassification (p=0.003), and dose administered in the tumor (p=0.001). Only one patient had a severe adverse reaction, developing posttreatment liver failure resulting in death.

CONCLUSIONS

Radioembolization is safe and efficacious in the treatment of patients with hepatocellular carcinoma. Liver function and the doses received by the tumor are key parameters for the efficacy of treatment. The increase in the scientific evidence supports the inclusion of this technique in treatment guidelines.

Utilizing 3D Slicer to incorporate tomographic images into GATE Monte Carlo simulation for personalized dosimetry in yttrium-90 radioembolization

PURPOSE

Monte Carlo (MC) simulation is an important technique that can help design advanced and challenging experimental setups. GATE (Geant4 application for tomographic emission) is a useful simulation toolkit for applications in nuclear medicine. Transarterial radioembolization is a treatment for liver cancer, where microspheres embedded with yttrium-90 (⁹⁰ Y) are administered intra-arterially to the tumor. Personalized dosimetry for this treatment may provide higher dosimetry accuracy compared to the conventional partition model (PM) calculation. However, incorporation of three-dimensional tomographic input data into MC simulation is an intricate process. In this article, 3D Slicer, free and open-source software, was utilized for the incorporation of patient tomographic images into GATE to demonstrate the feasibility of personalized dosimetry in hepatic radioembolization with ⁹⁰ Y.

METHODS

In this article, the steps involved in importing, segmenting, and registering tomographic images using 3D Slicer were thoroughly described, before importing them into GATE for MC simulation. The absorbed doses estimated using GATE were then compared with that of PM. SlicerRT, a 3D Slicer extension, was then used to visualize the isodose from the MC simulation.

RESULTS

A workflow diagram consisting of all the steps taken in the utilization of 3D Slicer for personalized dosimetry in ⁹⁰ Y radioembolization has been presented in this article. In comparison to the MC simulation, the absorbed doses to the tumor and normal liver were overestimated by PM by 105.55% and 20.23%, respectively, whereas for lungs, the absorbed dose estimated by PM was underestimated by 25.32%. These values were supported by the isodose distribution obtained via SlicerRT, suggesting the presence of beta particles outside the volumes of interest. These findings demonstrate the importance of personalized dosimetry for a more accurate absorbed dose estimation compared to PM.

CONCLUSION

The methodology provided in this study can assist users (especially students or researchers who are new to MC simulation) in navigating intricate steps required in the importation of tomographic data for MC simulation. These steps can also be utilized for other radiation therapy related applications, not necessarily limited to internal dosimetry.

Prediction of Lung Shunt Fraction for Yttrium-90 Treatment of Hepatic Tumors Using Dynamic Contrast Enhanced MRI with Quantitative Perfusion Processing

There is no noninvasive method to estimate lung shunting fraction (LSF) in patients with liver tumors undergoing Yttrium-90 (Y90) therapy. We propose to predict LSF from noninvasive dynamic contrast enhanced (DCE) MRI using perfusion quantification. Two perfusion quantification methods were used to process DCE MRI in 25 liver tumor patients: Kety's tracer kinetic modeling with a delay-fitted global arterial input function (AIF) and quantitative transport mapping (QTM) based on the inversion of transport equation using spatial deconvolution without AIF. LSF was measured on SPECT following Tc-99m macroaggregated albumin (MAA) administration via hepatic arterial catheter. The patient cohort was partitioned into a low-risk group (LSF ≤ 10%) and a high-risk group (LSF > 10%). Results: In this patient cohort, LSF was positively correlated with QTM velocity |u| (r = 0.61, F = 14.0363, p = 0.0021), and no significant correlation was observed with Kety's parameters, tumor volume, patient age and gender. Between the low LSF and high LSF groups, there was a significant difference for QTM |u| (0.0760 ± 0.0440 vs. 0.1822 ± 0.1225 mm/s, p = 0.0011), and Kety's Ktrans (0.0401 ± 0.0360 vs 0.1198 ± 0.3048, p = 0.0471) and Ve (0.0900 ± 0.0307 vs. 0.1495 ± 0.0485, p = 0.0114). The area under the curve (AUC) for distinguishing between low LSF and high LSF was 0.87 for |u|, 0.80 for Ve and 0.74 for Ktrans. Noninvasive prediction of LSF is feasible from DCE MRI with QTM velocity postprocessing.

Hepatic decompensation after transarterial radioembolization: A retrospective analysis of risk factors and outcome in patients with hepatocellular carcinoma

Transarterial radioembolization (TARE) is a well-established therapy for intermediate and advanced tumor stages of hepatocellular carcinoma (HCC). Treatment-associated toxicities are rare. Previous studies have outlined that the prognosis after TARE is determined primarily by tumor stage and liver function. The subset of patients benefiting from TARE remains to be defined. Sixty-one patients with HCC treated with TARE between 2015 and 2020 were retrospectively included in the study. Hepatic decompensation was defined as an increase of bilirubin or newly developed ascites that was not explained by tumor progression within 3 months after TARE. Predictive factors of hepatic decompensation and prognostic factors were assessed. Hepatic decompensation was observed in 27.9% (n = 17) of TARE-treated patients during follow-up. Albumin-bilirubin (ALBI) score at baseline and radiation dose on nontumor liver proved to be independent risk factors for the development of hepatic decompensation in multivariable regression models (ALBI score: odds ratio [OR] 6.425 [1.735;23.797], p < 0.005; radiation dose: OR 1.072 [1.016;1.131], p < 0.011). The occurrence of hepatic decompensation markedly impaired the prognosis of the patients. Survival was significantly worsened. Hepatic decompensation has shown to be an independent negative prognostic factor for death, adjusted for Barcelona Clinic Liver Cancer stage, age and ALBI grade (hazard ratio 5.694 [2.713;11.952], p < 0.001). Conclusion: Hepatic decompensation after TARE for HCC treatment is a highly relevant complication with major effects on the prognosis of patients. Main risk factors are the pretreatment ALBI score and radiation dose. There is an urgent need to define safe cutoff values and exclusion criteria for TARE to limit complications and improve patient outcomes.

Concepts and methods for the dosimetry of radioembolisation of the liver with Y-90-loaded microspheres

This article aims at presenting in a didactic way, dosimetry concepts and methods that are relevant for radio-embolization of the liver with 90Y-microspheres. The application of the medical internal radiation dose formalism to radio-embolization is introduced. This formalism enables a simplified dosimetry, where the absorbed dose in a given tissue depends on only its mass and initial activity. This is applied in the single-compartment method, partition model, for the liver, tumour and lung dosimetry, and multi-compartment method, allowing identification of multiple tumours. Voxel-based dosimetry approaches are also discussed. This allows taking into account the non-uniform uptake within a compartment, which translates into a non-uniform dose distribution, represented as a dose-volume histogram. For this purpose, dose-kernel convolution allows propagating the energy deposition around voxel-sources in a computationally efficient manner. Alternatively, local-energy deposition is preferable when the spatial resolution is comparable or larger than the beta-particle path. Statistical tools may be relevant in establishing dose-effect relationships in a given population. These include tools such as the logistic regression or receiver operator characteristic analysis. Examples are given for illustration purpose. Moreover, tumour control probability modelling can be assessed through the linear-quadratic model of Lea and Catcheside and its counterpart, the normal-tissue complication probability model of Lyman, which is suitable to the parallel structure of the liver. The selectivity of microsphere administration allows tissue sparing, which can be considered with the concept of equivalent uniform dose, for which examples are also given. The implication of microscopic deposition of microspheres is also illustrated through a liver toxicity model, even though it is not clinically validated. Finally, we propose a reflection around the concept of therapeutic index (TI), which could help tailor treatment planning by determining the treatment safety through the evaluation of TI based on treatment-specific parameters.

The American Brachytherapy Society consensus statement for permanent implant brachytherapy using Yttrium-90 microsphere radioembolization for liver tumors

PURPOSE

To develop a multidisciplinary consensus for high quality multidisciplinary implementation of brachytherapy using Yttrium-90 (90Y) microspheres transarterial radioembolization (90Y TARE) for primary and metastatic cancers in the liver.

METHODS AND MATERIALS

Members of the American Brachytherapy Society (ABS) and colleagues with multidisciplinary expertise in liver tumor therapy formulated guidelines for 90Y TARE for unresectable primary liver malignancies and unresectable metastatic cancer to the liver. The consensus is provided on the most recent literature and clinical experience.

RESULTS

The ABS strongly recommends the use of 90Y microsphere brachytherapy for the definitive/palliative treatment of unresectable liver cancer when recommended by the multidisciplinary team. A quality management program must be implemented at the start of 90Y TARE program development and follow-up data should be tracked for efficacy and toxicity. Patient-specific dosimetry optimized for treatment intent is recommended when conducting 90Y TARE. Implementation in patients on systemic therapy should account for factors that may enhance treatment related toxicity without delaying treatment inappropriately. Further management and salvage therapy options including retreatment with 90Y TARE should be carefully considered.

CONCLUSIONS

ABS consensus for implementing a safe 90Y TARE program for liver cancer in the multidisciplinary setting is presented. It builds on previous guidelines to include recommendations for appropriate implementation based on current literature and practices in experienced centers. Practitioners and cooperative groups are encouraged to use this document as a guide to formulate their clinical practices and to adopt the most recent dose reporting policies that are critical for a unified outcome analysis of future effectiveness studies.

Study Protocol: Efficacy and Safety of Radioembolization (REM) as an Early Modality (EM) Therapy for Metastatic Breast Cancer (BR) to the Liver with Y90 (REMEMBR Y90)

PURPOSE

The primary objective of the REMEMBR Y90 study is to evaluate the efficacy of Yttrium-90 (Y90) radioembolization in patients with breast cancer metastases to the liver as a 2nd or 3rd line treatment option with systemic therapy by assessing liver-specific and overall progression-free survival. Secondary objectives include quality of life, overall survival benefit, and toxicity in relation to patients' tumor biology.

MATERIALS AND METHODS

This trial is a multi-center, prospective, Phase 2, open-label, IRB-approved, randomized control trial in the final phases of activation. Eligible patients include those over 18 years of age with metastatic breast cancer to the liver with liver-only or liver-dominant disease, and history of tumor progression on 1-2 lines of chemotherapy. 60 patients will be randomized to radioembolization with chemotherapy versus chemotherapy alone. Permissible regimens include capecitabine, eribulin, vinorelbine, and gemcitabine within 2 weeks of enrollment for every patient. Patients receiving radioembolization will receive lobar or segmental treatment within 1-6 weeks of enrollment depending on their lesion. After final radioembolization, patients will receive clinical and imaging follow-up every 12-16 weeks for two years, including contrast-enhanced computed tomography or magnetic resonance imaging of the abdomen and whole-body positron emission tomography/computed tomography.

DISCUSSION

This study seeks to elucidate the clinical benefit and toxicity of Y90 in patients with metastatic breast cancer to the liver who are receiving minimal chemotherapy. Given previous data, it is anticipated that the use of Y90 and chemotherapy earlier in the metastatic disease course would improve survival outcomes and reduce toxicity.

LEVEL OF EVIDENCE

Level 1b, Randomized Controlled Trial.

TRIAL REGISTRATION NUMBER

NCT05315687 on clinicaltrials.gov.

ALBI grade for outcome prediction in patients affected by hepatocellular carcinoma treated with transarterial radioembolization

Introduction and aim

Diagnosis of hepatocellular carcinoma (HCC) often occurs when the disease is unresectable and therapeutic options are limited. The extent of disease and liver function according to Child-Pugh (C-P) classification are the main prognostic factors guiding clinicians in the management of HCC. The integration of albumin-bilirubin (ALBI) grade is emerging to assess liver function on account of its objectivity and reproducibility. Our aim was to investigate the value of the ALBI grade in predicting the outcome in patients treated with transarterial radioembolization (TARE).

Methods

We retrospectively enrolled patients with advanced and unresectable HCC treated with TARE in our institution. All patients underwent a preliminary dosimetric study before Yttrium-90 resin microsphere TARE. Barcelona Clinic Liver Cancer (BCLC), C-P, and ALBI scores were established at the time of TARE. Overall survival (OS), progression-free survival (PFS), and survival after TARE were assessed with the Kaplan-Meier method. Survival analyses were stratified according to ALBI grade, C-P, and BCLC classification. Univariate and multivariate Cox proportional regression models determined the association between prognostic factors and clinical outcomes.

Results

In total, 72 patients were included in the study, showing an OS of 51 months. The ALBI grade identified groups of patients with different prognoses both in the whole cohort and within the C-P classes, especially between ALBI 1 and ALBI 2. This result is confirmed also within BCLC classes. In treatment naïve patients, the ALBI grade was not able to predict outcomes, whereas the presence and degree of portal vein thrombosis (PVT) significantly affected prognosis.

Conclusions

The ALBI grade provided a more accurate prognostic stratification than the C-P classification in patients with intermediate and advanced HCC treated with TARE. However, the outcome of HCC is affected not only by liver function but also by disease-related characteristics, such as disease burden and degree of PVT. Including the ALBI grade in clinical guidelines may improve the management of patients affected by HCC.

Milestones in dosimetry for nuclear medicine therapy

Nuclear Medicine therapy has reached a critical juncture with an unprecedented number of patients being treated and an extensive list of new radiopharmaceuticals under development. Since the early applications of these treatments dosimetry has played a vital role in their development, in both aiding optimisation and enhancing safety and efficacy. To inform the future direction of this field, it is useful to reflect on the scientific and technological advances that have occurred since those early uses. In this review, we explore how dosimetry has evolved over the years and discuss why such initiatives were conceived and the importance of maintaining standards within our practise. Specific milestones and landmark publications are highlighted and a thematic review and significant outcomes during each decade are presented.

Selective Internal Radiation Therapy with Yttrium-90 for Intrahepatic Cholangiocarcinoma: A Systematic Review on Post-Treatment Dosimetry and Concomitant Chemotherapy

Selective internal radiation therapy (SIRT) with yttrium-90 (90Y)-loaded microspheres is increasingly used for the treatment of Intrahepatic Cholangiocarcinoma (ICC). Dosimetry verifications post-treatment are required for a valid assessment of any dose-response relationship. We performed a systematic review of the literature to determine how often clinics conducted post-treatment dosimetry verification to measure the actual radiation doses delivered to the tumor and to the normal liver in patients who underwent SIRT for ICC, and also to explore the corresponding dose-response relationship. We also investigated other factors that potentially affect treatment outcomes, including the type of microspheres used and concomitant chemotherapy. Out of the final 47 studies that entered our study, only four papers included post-treatment dosimetry studies after SIRT to quantitatively assess the radiation doses delivered. No study showed that one microsphere type provided a benefit over another, one study demonstrated better imaging-based response rates associated with the use of glass-based TheraSpheres, and two studies found similar toxicity profiles for different types of microspheres. Gemcitabine and cisplatin were the most common chemotherapeutic drugs for concomitant administration with SIRT. Future studies of SIRT for ICC should include dosimetry to optimize treatment planning and post-treatment radiation dosage measurements in order to reliably predict patient responses and liver toxicity.

Technical Note: Respiratory impacts on static and respiratory gated 99m Tc-MAA SPECT/CT for liver radioembolization- A simulation study

PURPOSE

We aimed to evaluate respiratory impacts on static and respiratory gated (RG) ^99m Tc-MAA SPECT in terms of respiratory motion (RM) blur, attenuation correction (AC) and volume-of-interest (VOI) segmentation on lung shunt faction (LSF) and tumor-to-normal liver ratio (TNR) estimation for liver radioembolization therapy planning.

METHODS

The XCAT phantom was used to simulate a population of 300 phantoms, modelling various anatomical variations, tumor characteristics, respiratory motion amplitudes, LSFs and TNRs. One hundred and twenty noisy projections of average activity maps near end-expiration (End-EX) and whole respiratory cycle were simulated analytically, modeling attenuation and geometric collimator-detector-response (GCDR). The OS-EM algorithm was employed for reconstruction, modeling AC and GCDR. RM effect was evaluated for static SPECT, while AC and VOI mismatch effects were investigated independently and together for static and RG SPECT utilizing one gate, i.e., End-EX. LSF and TNR errors were measured based on the ground truth. Lesions with different characteristics were also investigated for static and RG SPECT.

RESULTS

RM overestimates LSF and underestimates TNR. The VOI mismatch caused the largest errors in both RG and static SPECT for LSF and TNR estimation, reaching 160% and -52% correspondingly with extremely mismatched VOIs for RG SPECT, even larger than those for static SPECT. With matched AC and VOIs, RG SPECT has better performance than static SPECT. Larger TNR errors are associated with tumors of smaller sizes and higher TNR for static SPECT.

CONCLUSIONS

The VOI segmentation mismatch has a stronger impact, followed by RM and AC in static ^99m Tc-MAA SPECT/CT. This effect is more pronounced for RG SPECT. When VOI masks are derived from a matched CT, RG SPECT is generally superior to static SPECT for LSF and TNR estimation. The performance of RG SPECT could be worse than static SPECT when a mismatched CT is used for segmentation. This article is protected by copyright. All rights reserved.

EANM procedure guideline for the treatment of liver cancer and liver metastases with intra-arterial radioactive compounds

Primary liver tumours (i.e. hepatocellular carcinoma (HCC) or intrahepatic cholangiocarcinoma (ICC)) are among the most frequent cancers worldwide. However, only 10-20% of patients are amenable to curative treatment, such as resection or transplant. Liver metastases are most frequently caused by colorectal cancer, which accounts for the second most cancer-related deaths in Europe. In both primary and secondary tumours, radioembolization has been shown to be a safe and effective treatment option. The vast potential of personalized dosimetry has also been shown, resulting in markedly increased response rates and overall survival. In a rapidly evolving therapeutic landscape, the role of radioembolization will be subject to changes. Therefore, the decision for radioembolization should be taken by a multidisciplinary tumour board in accordance with the current clinical guidelines. The purpose of this procedure guideline is to assist the nuclear medicine physician in treating and managing patients undergoing radioembolization treatment. PREAMBLE: The European Association of Nuclear Medicine (EANM) is a professional non-profit medical association that facilitates communication worldwide among individuals pursuing clinical and research excellence in nuclear medicine. The EANM was founded in 1985. These guidelines are intended to assist practitioners in providing appropriate nuclear medicine care for patients. They are not inflexible rules or requirements of practice and are not intended, nor should they be used, to establish a legal standard of care. The ultimate judgment regarding the propriety of any specific procedure or course of action must be made by medical professionals taking into account the unique circumstances of each case. Thus, there is no implication that an approach differing from the guidelines, standing alone, is below the standard of care. To the contrary, a conscientious practitioner may responsibly adopt a course of action different from that set out in the guidelines when, in the reasonable judgment of the practitioner, such course of action is indicated by the condition of the patient, limitations of available resources or advances in knowledge or technology subsequent to publication of the guidelines. The practice of medicine involves not only the science but also the art of dealing with the prevention, diagnosis, alleviation and treatment of disease. The variety and complexity of human conditions make it impossible to always reach the most appropriate diagnosis or to predict with certainty a particular response to treatment. Therefore, it should be recognised that adherence to these guidelines will not ensure an accurate diagnosis or a successful outcome. All that should be expected is that the practitioner will follow a reasonable course of action based on current knowledge, available resources and the needs of the patient to deliver effective and safe medical care. The sole purpose of these guidelines is to assist practitioners in achieving this objective.

A prospective, multicenter, open-label, single-arm clinical trial design to evaluate the safety and efficacy of 90Y resin microspheres for the treatment of unresectable HCC: the DOORwaY90 (Duration Of Objective Response with arterial Ytrrium-90) study

Background

Selective internal radiation therapy (SIRT) with yttrium-90 (⁹⁰Y) resin microspheres is an established locoregional treatment option for unresectable hepatocellular carcinoma (HCC), which delivers a lethal dose of radiation to hepatic tumors, while sparing surrounding healthy tissue. DOORwaY90 is a prospective, multicenter, open-label, single arm study, designed to evaluate the safety and effectiveness of ⁹⁰Y resin microspheres as first-line treatment in patients with unresectable/unablatable HCC. It is unique in that it is the first study with resin microspheres to utilize a personalized ⁹⁰Y dosimetry approach, and independent review for treatment planning and response assessment.

Methods

Eligibility criteria include unresectable/unablatable HCC, Barcelona Clinic Liver Cancer stage A, B1, B2, or C with a maximal single tumor diameter of ≤ 8 cm, and a sum of maximal tumor diameters of ≤ 12 cm, and at least one tumor ≥ 2 cm (long axis) per localized, modified Response Evaluation Criteria in Solid Tumors. Partition model dosimetry is used to determine the optimal dose; the target mean dose to tumor is ≥ 150 Gy. Patients are assessed at baseline and at regular intervals up until 12 months of treatment for response rates, safety, and quality of life (QoL). Post-treatment dosimetry is used to assess dose delivered to tumor and consider if retreatment is necessary. The co-primary endpoints are best objective response rate and duration of response. Secondary endpoints include grade ≥ 3 toxicity, QoL, and incidence of liver resection and transplantation post SIRT. Target recruitment is 100 patients.

Discussion

The results of this trial should provide further information on the potential use of SIRT with ⁹⁰Y resin microspheres as first-line therapy for unresectable HCC.

Trial registration

Clinicaltrials.gov; NCT04736121; date of 1st registration, January 27, 2021, https://clinicaltrials.gov/ct2/show/NCT04736121.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12876-022-02204-1.

Clinical outcome of Yttrium-90 selective internal radiation therapy (Y-90 SIRT) in unresectable hepatocellular carcinoma: Experience from a tertiary care center

Background and aim

Whereas Yttrium-90 selective internal radiation therapy (Y-90 SIRT) was shown to improve local tumor control in non-Asian population, the efficacy of this therapy for Asian population in real-world setting remains poorly detailed. We aimed to determine outcomes and identify predictors of response in hepatocellular carcinoma (HCC) patients treated by Y-90 SIRT.

Methods

We retrospectively enrolled 52 HCC patients receiving Y-90 SIRT at our tertiary center between 2014 and 2019. Overall survival (OS), progression free survival (PFS), and predictive factors were determined by Kaplan-Meier method and Cox-proportional hazard analysis.

Results

Of the 52 patients (81% male, mean age 64.9 years), 71% and 29% were classified as Barcelona Clinic Liver Cancer stage C and B HCC, respectively; 63% had portal vein thrombosis, and 35% had objective tumor response defined by the modified Response Evaluation Criteria in Solid Tumors (mRECIST) criteria. OS and PFS were 11.0 and 2.4 months, respectively. Two patients were successfully down-staged and further underwent surgical resection. Multifocal lesion, alpha-fetoprotein (AFP) ≥200 ng/mL, and Eastern Cooperative Oncology Group (ECOG) score ≥1 were significantly associated with poor survival, with adjusted hazard ratio (95% confidence interval) of 7.7 (2.0-29.8), 5.4 (2.0-14.7), and 3.1 (1.0-9.6), respectively (all in P < 0.05).

Conclusions

Y-90 SIRT is an effective treatment for the local tumor control of HCC without serious adverse events. Single lesion, AFP level and ECOG status were predictors of response.

Comparison of Chemoembolization, Radioembolization, and Transarterial Ethanol Ablation for Huge Hepatocellular Carcinoma (≥ 10 cm) in Tumour Response and Long-Term Survival Outcome

PURPOSE

To compare transarterial chemoembolization (TACE), transarterial radioembolization using Yttrium-90 (TARE), and transarterial ethanol ablation (TEA) for huge hepatocellular carcinoma (HCC) in treatment responses and long-term survival outcomes.

MATERIALS AND METHODS

In this retrospective study approved by institutional committee, inclusion criteria were tumour ≥ 10 cm, newly diagnosed, treatment naïve, Child A, Performance Score 0 or 1, no venous invasion or extrahepatic disease on contrast-enhanced CT or MRI. There were 107 patients (Supportive Care [SC] 17, TACE 54, TARE 17, TEA 19). Survival outcomes of SC and TACE were compared (TACE selected as benchmark for transarterial treatments). Tumour response and overall survival (OS) of the three groups were compared.

RESULTS

OS of TACE (vs. SC) was significantly longer (9.9 [5.9, 24.1] months versus 2.8 [1.5, 10.2], p = 0.001). Complete response of TEA was significantly better (TEA 10/19 [52.6%] versus TARE 2/17 [12.5%], p = 0.013, versus TACE 9/54 [16.7%], p = 0.002). OS of TEA (vs. TACE) was significantly longer (21.6 [12, 41] months versus 9.9 [5.9, 24.1], p = 0.014, hazard ratio 0.6 (0.3, 1). OS of TEA (vs. TARE) was longer (21.6 [12, 41] months versus 11.9 [7, 28.7], p = 0.082, hazard ratio 0.6 (0.3, 1.3) in favour of TEA).

CONCLUSION

In patients with huge HCC, transarterial treatment as represented by TACE had a survival benefit over supportive care. In this retrospective analysis, TEA was associated with better tumour response and survival outcome as compared to TACE or TARE; therefore, transarterial treatment could be useful for prolonging patient survival, and TEA could be a preferred option.

Segmentation-guided multi-modal registration of liver images for dose estimation in SIRT

Purpose

Selective internal radiation therapy (SIRT) requires a good liver registration of multi-modality images to obtain precise dose prediction and measurement. This study investigated the feasibility of liver registration of CT and MR images, guided by segmentation of the liver and its landmarks. The influence of the resulting lesion registration on dose estimation was evaluated.

Methods

The liver segmentation was done with a convolutional neural network (CNN), and the landmarks were segmented manually. Our image-based registration software and its liver-segmentation-guided extension (CNN-guided) were tuned and evaluated with 49 CT and 26 MR images from 20 SIRT patients. Each liver registration was evaluated by the root mean square distance (RMSD) of mean surface distance between manually delineated liver contours and mass center distance between manually delineated landmarks (lesions, clips, etc.). The root mean square of RMSDs (RRMSD) was used to evaluate all liver registrations. The CNN-guided registration was further extended by incorporating landmark segmentations (CNN&LM-guided) to assess the value of additional landmark guidance. To evaluate the influence of segmentation-guided registration on dose estimation, mean dose and volume percentages receiving at least 70 Gy (V70) estimated on the ^99mTc-labeled macro-aggregated albumin (^99mTc-MAA) SPECT were computed, either based on lesions from the reference ^99mTc-MAA CT (reference lesions) or from the registered floating CT or MR images (registered lesions) using the CNN- or CNN&LM-guided algorithms.

Results

The RRMSD decreased for the floating CTs and MRs by 1.0 mm (11%) and 3.4 mm (34%) using CNN guidance for the image-based registration and by 2.1 mm (26%) and 1.4 mm (21%) using landmark guidance for the CNN-guided registration. The quartiles for the relative mean dose difference (the V70 difference) between the reference and registered lesions and their correlations [25th, 75th; r] are as follows: [− 5.5% (− 1.3%), 5.6% (3.4%); 0.97 (0.95)] and [− 12.3% (− 2.1%), 14.8% (2.9%); 0.96 (0.97)] for the CNN&LM- and CNN-guided CT to CT registrations, [− 7.7% (− 6.6%), 7.0% (3.1%); 0.97 (0.90)] and [− 15.1% (− 11.3%), 2.4% (2.5%); 0.91 (0.78)] for the CNN&LM- and CNN-guided MR to CT registrations.

Conclusion

Guidance by CNN liver segmentations and landmarks markedly improves the performance of the image-based registration. The small mean dose change between the reference and registered lesions demonstrates the feasibility of applying the CNN&LM- or CNN-guided registration to volume-level dose prediction. The CNN&LM- and CNN-guided registrations for CTs can be applied to voxel-level dose prediction according to their small V70 change for most lesions. The CNN-guided MR to CT registration still needs to incorporate landmark guidance for smaller change of voxel-level dose estimation.

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).

Automated segmentation of lung, liver, and liver tumors from Tc-99m MAA SPECT/CT images for Y-90 radioembolization using convolutional neural networks

PURPOSE

90 Y selective internal radiation therapy (SIRT) has become a safe and effective treatment option for liver cancer. However, segmentation of target and organ-at-risks is labor-intensive and time-consuming in 90 Y SIRT planning. In this study, we developed a convolutional neural network (CNN)-based method for automated lungs, liver, and tumor segmentation on 99m Tc-MAA SPECT/CT images for 90 Y SIRT planning.

METHODS

99m Tc-MAA SPECT/CT images and corresponding clinical segmentations were retrospectively collected from 56 patients who underwent 90 Y SIRT. The collected data were used to train three CNN-based segmentation algorithms for lungs, liver, and tumor segmentation. Segmentation performance was evaluated using the Dice similarity coefficient (DSC), surface DSC, and average symmetric surface distance (ASSD). Dosimetric parameters (volume, counts, and lung shunt fraction) were measured from the segmentation results and were compared with clinical reference segmentations.

RESULTS

The evaluation results show that the method can accurately segment lungs, liver, and tumor with median [interquartile range] DSCs of 0.98 [0.97-0.98], 0.91 [0.83-0.93], and 0.85 [0.71-0.88]; surface DSCs of 0.99 [0.97-0.99], 0.86 [0.77-0.93], and 0.85 [0.62-0.93], and ASSDs of 0.91 [0.69-1.5], 4.8 [2.6-8.4], and 4.7 [3.5-9.2] mm, respectively. Dosimetric parameters from the three segmentation networks show relationship with those from the reference segmentations. The overall segmentation took about 1 min per patient on an NVIDIA RTX-2080Ti GPU.

CONCLUSION

This work presents CNN-based algorithms to segment lungs, liver, and tumor from 99m Tc-MAA SPECT/CT images. The results demonstrated the potential of the proposed CNN-based segmentation method for assisting 90 Y SIRT planning while drastically reducing operator time.

Efficacy of voxel-based dosimetry map for predicting response to trans-arterial radioembolization therapy for hepatocellular carcinoma: a pilot study

OBJECTIVE

Typical clinical dosimetry models for trans-arterial radioembolization (TARE) assume uniform dose distribution in each tissue compartment. We performed simple voxel-based dosimetry using post-treatment 90Y PET following TARE with 90Y-resin microspheres and investigated its prognostic value in a pilot cohort.

METHOD

Ten patients with 14 hepatocellular carcinoma lesions who underwent TARE with 90Y-resin microspheres were retrospectively included. The partition model-based expected target tumor dose (TDp) was calculated using a pretreatment 99mTc-macroaggregated albumin scan. From post-treatment 90Y-microsphere PET and voxel-wise S-value kernels, voxel-based dose maps were produced and the absorbed dose of each lesion (TDv) was calculated. Heterogeneity of intratumoral absorbed doses was assessed using the SD and coefficient of variation of voxel doses. The response of each lesion was determined based on contrast-enhanced MRI or CT, or both. Lesion responses were classified as local control success or failure. Prognostic values of dosimetry parameters and clinicopathological factors were evaluated in terms of progression-free survival (PFS) of each lesion.

RESULTS

TDv was significantly different between local control success and failure groups, whereas tumor size, TDp and intratumoral dose heterogeneity were not. Univariate survival analysis identified serum aspartate transaminase level ≥40 IU/L, tumor size ≥66 mm and TDv <81 Gy as significant prognostic factors for PFS. However, only TDv was an independent predictive factor in the multivariate analysis (P = 0.022). There was a significant correlation between TDv and PFS (P = 0.009; r = 0.669).

CONCLUSIONS

In TARE, voxel-based dose index TDv can be estimated on post-treatment 90Y PET using a simple method. TDv was a more effective prognostic factor for TARE than TDp and clinicopathologic factors in this pilot study. Further studies are warranted on the role of voxel-based dose and dose distribution in TARE.

Antireflux catheter improves tumor targeting in liver radioembolization with resin microspheres

PURPOSE

We aimed to determine whether antireflux (ARC) catheter may result in better tumor targeting in liver radioembolization using 90Y-resin microspheres.

METHODS

Patients treated with resin microspheres for hepatocellular carcinoma (HCC) and secondary liver malignancies were retrospectively analyzed. All patients underwent a 99mTc-macroaggregated albumin (99mTc-MAA) single photon emission computed tomography (SPECT) following the planning arteriography with a conventional end-hole catheter. For 90Y-microspheres injection, two groups were defined depending on the type of catheter used: an ARC group (n=38) and a control group treated with a conventional end-hole catheter (n=23). 90Y positron emission tomography computed tomography (PET/CT) was performed after the therapeutic arteriography. The choice of the catheter was not randomized, but left to the choice of the interventional radiologist. 99mTc-MAA SPECT and 90Y PET/CT were co-registered with the baseline imaging to determine a tumor to normal liver ratio (T/NL[MAA or 90Y]) and tumor dose (TD[MAA or 90Y]) for the planning and therapy.

RESULTS

Overall, 38 patients (115 lesions) and 23 patients (75 lesions) were analyzed in the ARC and control groups, respectively. In the ARC group, T/NL90Y and TD90Y were significantly higher than T/NLMAA and TDMAA. Median (IQR) T/NL90Y was 2.16 (2.15) versus 1.74 (1.43) for T/NLMAA (p < 0.001). Median (IQR) TD90Y was 90.96 Gy (98.31 Gy) versus 73.72 Gy (63.82 Gy) for TDMAA (p < 0.001). In this group, the differences were highly significant for neuroendocrine metastases (NEM) and HCC and less significant for colorectal metastases (CRM). In the control group, no significant differences were demonstrated.

CONCLUSION

The use of an ARC significantly improves tumor deposition in liver radioembolization with resin microspheres.

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.

Radiation Lobectomy: An Overview of Concept and Applications, Technical Considerations, Outcomes

Surgical resection has long been considered curative for patients with early-stage hepatocellular carcinoma (HCC). However, inadequate future liver remnant (FLR) renders many patients not amenable to surgery. Recently, lobar administration of yttrium-90 (Y90) radioembolization has been utilized to induce FLR hypertrophy while providing disease control, eventually facilitating resection in patients with hepatic malignancy. This has been termed "radiation lobectomy (RL)." The concept is evolving, with modified approaches combining RL and high-dose curative-intent radioembolization (radiation segmentectomy) to achieve tumor ablation. This article provides an overview of the concept and applications of RL, including technical considerations and outcomes in patients with hepatic malignancies.

Assessment of radiation sensitivity of unresectable intrahepatic cholangiocarcinoma in a series of patients submitted to radioembolization with yttrium-90 resin microspheres

Radioembolization is a valuable therapeutic option in patients with unresectable intrahepatic cholangiocarcinoma. The essential implementation of the absorbed dose calculation methods should take into account also the specific tumor radiosensitivity, expressed by the α parameter. Purpose of this study was to retrospectively calculate it in a series of patients with unresectable intrahepatic cholangiocarcinoma submitted to radioembolization. Twenty-one therapeutic procedures in 15 patients were analysed. Tumor absorbed doses were calculated processing the post-therapeutic ⁹⁰Y-PET/CT images and the pre-treatment contrast-enhanced CT scans. Tumor absorbed dose and pre- and post-treatment tumor volumes were used to calculate α and α_3D parameters (dividing targeted liver in n voxels of the same volume with specific voxel absorbed dose). A tumor volume reduction was observed after treatment. The median of tumor average absorbed dose was 93 Gy (95% CI 81–119) and its correlation with the residual tumor mass was statistically significant. The median of α and α_3D parameters was 0.005 Gy⁻¹ (95% CI 0.004–0.008) and 0.007 Gy⁻¹ (95% CI 0.005–0.015), respectively. Multivariate analysis showed tumor volume and tumor absorbed dose as significant predictors of the time to tumor progression. The knowledge of radiobiological parameters gives the possibility to decide the administered activity in order to improve the outcome of the treatment.

Lung shunt fraction calculation using 99mTc-MAA SPECT/CT imaging for 90Y microsphere selective internal radiation therapy of liver tumors

BACKGROUND

^99mTc-macroaggregated albumin (^99mTc-MAA) scintigraphy is utilized in treatment planning for Yttrium-90 (⁹⁰Y) Selective Internal Radiation Therapy (SIRT) of liver tumors to evaluate hepatopulmonary shunting by calculating the lung shunt fraction (LSF). The purpose of this study was to evaluate if LSF calculation using SPECT/CT instead of planar gamma camera imaging is more accurate and if this can potentially lead to more effective treatment planning of hepatic lesions while avoiding excessive pulmonary irradiation.

RESULTS

LSF calculation was obtained using two different methodologies in 85 cases from consecutive patients intended to receive ⁹⁰Y SIRT. The first method was based on planar gamma camera imaging in the anterior and posterior views with geometric mean calculation of the LSF from regions of interest of the liver and lungs. The second method was based on segmentation of the liver and lungs from SPECT/CT images of the thorax and abdomen. The differences in planar imaging versus SPECT/CT derived LSF values along with the estimated absorbed lung mean dose (LMD) were evaluated. The LSF values were higher in planar imaging versus SPECT/CT in 81/85 cases, with a mean value of 8.5% vs. 4.6% respectively; the difference was statistically significant using a paired t-test (alpha = 0.05). In those patients who received SIRT, the estimated absorbed LMD calculated with planar imaging was significantly higher than with SPECT/CT (t-test, P < 0.005). Repeated phantom experiments using an anthropomorphic torso phantom with variable ^99mTc activity concentrations for the liver and lungs were performed with the standard patient protocol, demonstrated improved accuracy of the LSF calculation based on SPECT/CT than planar imaging (mean overestimated value of 6% vs. 26%).

CONCLUSIONS

This study demonstrates that LSF calculation using planar imaging can be significantly overestimated while calculation using SPECT/CT imaging and appropriate segmentation tools can be more accurate. Minimizing the errors in obtaining the LSF can lead to more effective ⁹⁰Y SIRT treatment planning for hepatic tumors while ensuring the lung dose will not exceed the standard acceptable safety thresholds.

Accurate non-tumoral 99mTc-MAA absorbed dose prediction to plan optimized activities in liver radioembolization using resin microspheres

AIM

The manufacturers' recommended methods to calculate delivered activities in liver radioembolization are simplistic and only slightly personalized. Activity planning could also be based on a ^99mTc-macroaggregated albumin SPECT/CT (MAA) using the partition model but its accuracy is controversial. This study evaluates the dose parameters in the normal liver and in the tumor compartments using MAA SPECT/CT (pre-therapeutic imaging) and ⁹⁰Y TOF-PET/CT (post-therapy imaging). Finally, we propose a prescription of the activity as a function of the normal liver MAA distribution.

METHOD

66 procedures of RE (with resin microspheres) corresponding to 171 lesions were analyzed. Tumor to normal targeted liver uptake (T/NTL), tumor absorbed dose (TD) and whole normal liver absorbed (WNLD) were assessed with MAA and ⁹⁰Y imaging. Secondly, activities were recalculated using the MAA distribution in the normal liver compartment to reach the maximal tolerable liver dose. These Activities were compared to activities defined with the BSA method.

RESULTS

Compared to ⁹⁰Y imaging, our study demonstrated an accurate estimation of the WNLD using MAA imaging (Pearson's R = 0.97, p < 0.001). On the contrary, significant variations were found for TD (R = 0.65, p < 0.001). The MAA T/NTL ratio has a 85% positive predictive value in identifying patients who will get a ⁹⁰Y T/NTL ratio above 1.5. Moreover, activities calculated using the MAA distribution in the normal liver compartment were significantly higher to activities defined with the BSA method.

CONCLUSION

Whole normal liver absorbed doses are accurately predicted with MAA imaging and could be used to optimize the activity planning.

Radioembolization vs sorafenib in locally advanced hepatocellular carcinoma with portal vein tumor thrombosis: A propensity score and Bayesian analysis

OBJECTIVE

In this study we aimed to compare patient outcomes between the use of transarterial radioembolization (TARE) and sorafenib in patients with hepatocellular carcinoma (HCC) and intrahepatic portal vein tumor thrombosis (PVTT).

METHODS

A total of 65 patients with HCC and intrahepatic PVTT treated in five Italian hospitals between 2012 and 2018 were included in the analysis. Those with any previous treatment, extension of PVTT to the main portal tract and extrahepatic involvement were excluded. Propensity score matching analysis and Bayesian model averaging analysis were performed.

RESULTS

Of the 41 patients treated with TARE and 24 with sorafenib, 11 patients were downstaged to curative-intent surgery (liver transplant in three and hepatectomy in eight), including 10 treated with TARE and one with sorafenib. TARE was more effective than sorafenib in downstaging patients to surgery, achieving a mean survival of 54 months. In the 54 patients without downstaging after treatment, of whom 31 were treated with TARE and 23 with sorafenib, median survival was 20.3 and 9.1 months, respectively (P = 0.001), with different 1-, 2- and 3-year OS rates (64.5%, 42.6% and 37.3% vs 39.1%, 13.0% and 0%). Both propensity score and Bayesian model averaging confirmed an improvement in overall survival in the TARE group compared with sorafenib treatment.

CONCLUSIONS

TARE was more effective than sorafenib in downstaging patients with HCC to surgery, providing a significant improvement in survival. Even in patients who were not downstaged to surgery, survival appeared to be superior with TARE over sorafenib.

Yttrium-90 quantitative phantom study using digital photon counting PET

BACKGROUND

PET imaging of 90Y-microsphere distribution following radioembolisation is challenging due to the count-starved statistics from the low branching ratio of e+/e- pair production during 90Y decay. PET systems using silicon photo-multipliers have shown better 90Y image quality compared to conventional photo-multiplier tubes. The main goal of the present study was to evaluate reconstruction parameters for different phantom configurations and varying listmode acquisition lengths to improve quantitative accuracy in 90Y dosimetry, using digital photon counting PET/CT.

METHODS

Quantitative PET and dosimetry accuracy were evaluated using two uniform cylindrical phantoms specific for PET calibration validation. A third body phantom with a 9:1 hot sphere-to-background ratio was scanned at different activity concentrations of 90Y. Reconstructions were performed using OSEM algorithm with varying parameters. Time-of-flight and point-spread function modellings were included in all reconstructions. Absorbed dose calculations were carried out using voxel S-values convolution and were compared to reference Monte Carlo simulations. Dose-volume histograms and root-mean-square deviations were used to evaluate reconstruction parameter sets. Using listmode data, phantom and patient datasets were rebinned into various lengths of time to assess the influence of count statistics on the calculation of absorbed dose. Comparisons between the local energy deposition method and the absorbed dose calculations were performed.

RESULTS

Using a 2-mm full width at half maximum post-reconstruction Gaussian filter, the dosimetric accuracy was found to be similar to that found with no filter applied but also reduced noise. Larger filter sizes should not be used. An acquisition length of more than 10 min/bed reduces image noise but has no significant impact in the quantification of phantom or patient data for the digital photon counting PET. 3 iterations with 10 subsets were found suitable for large spheres whereas 1 iteration with 30 subsets could improve dosimetry for smaller spheres.

CONCLUSION

The best choice of the combination of iterations and subsets depends on the size of the spheres. However, one should be careful on this choice, depending on the imaging conditions and setup. This study can be useful in this choice for future studies for more accurate 90Y post-dosimetry using a digital photon counting PET/CT.