Clinical evaluation of the partition model for estimating radiation doses from yttrium-90 microspheres in the treatment of hepatic cancer

90Y post-radioembolization clinical assessment with whole-body Biograph Vision Quadra PET/CT: image quality, tumor, liver and lung dosimetry

PURPOSE

Evaluation of 90Y liver radioembolization post-treatment clinical data using a whole-body Biograph Vision Quadra PET/CT to investigate the potential of protocol optimization in terms of scan time and dosimetry.

METHODS

17 patients with hepatocellular carcinoma with median (IQR) injected activity 2393 (1348-3298) MBq were included. Pre-treatment dosimetry plan was based on 99mTc-MAA SPECT/CT with Simplicit90Y™ and post-treatment validation with Quadra using Simplicit90Y™ and HERMIA independently. Regarding the image analysis, mean and peak SNR, the coefficient of variation (COV) and lesion-to-background ratio (LBR) were evaluated. For the post-treatment dosimetry validation, the mean tumor, whole liver and lung absorbed dose evaluation was performed using Simplicit90Y and HERMES. Images were reconstructed with 20-, 15-, 10-, 5- and 1- min sinograms with 2, 4, 6 and 8 iterations. Wilcoxon signed rank test was used to show statistical significance (p < 0.05).

RESULTS

There was no difference of statistical significance between 20- and 5- min reconstructed times for the peak SNR, COV and LBR. In addition, there was no difference of statistical significance between 20- and 1- min reconstructed times for all dosimetry metrics. Lung dosimetry showed consistently lower values than the expected. Tumor absorbed dose based on Simplicit90Y™ was similar to the expected while HERMES consistently underestimated significantly the measured tumor absorbed dose. Finally, there was no difference of statistical significance between expected and measured tumor, whole liver and lung dose for all reconstruction times.

CONCLUSION

In this study we evaluated, in terms of image quality and dosimetry, whole-body PET clinical images of patients after having been treated with 90Y microspheres radioembolization for liver cancer. Compared to the 20-min standard scan, the simulated 5-min reconstructed images provided equal image peak SNR and noise behavior, while performing also similarly for post-treatment dosimetry of tumor, whole liver and lung absorbed doses.

Microfluidic Fabrication of Silica Microspheres Infused with Positron Emission Tomography Imaging Agents

Selective internal radiation therapy (SIRT) is a treatment which delivers radioactive therapeutic microspheres via the hepatic artery to destroy tumorigenic tissue of the liver. However, the dose required varies significantly from patient to patient due to nuances in individual biology. Therefore, a positron emission tomography (PET) imaging surrogate, or radiotracer, is used to predict in vivo behavior of therapeutic Y-90 spheres. The ideal surrogate should closely resemble Y-90 microspheres in morphology for highest predictive accuracy. This work presents the fabrication of positron-emitting silica microspheres infused with PET radiotracers copper, fluorine, and gallium. A quick one-pot synthesis is used to create precursor sol, followed by droplet formation with flow-focusing microfluidics, and finally thermal treatment to yield 10-50 μm microspheres with narrow size distribution. Loading of the infused element is controllable in the sol synthesis, while the final sphere size is tunable based on microfluidic flow rates and device channel width. The system is then employed to make radioactive Ga-68 microspheres, which are tested for radioactivity and stability. The fabrication method can be completed within a few hours, depending on the desired microsphere quantity. A microfluidic system is applied to fabricate silica particles loaded with diverse elemental infusions, including radioactive Ga-68.

Non-Invasive Imaging Biomarkers to Predict the Hepatopulmonary Shunt Fraction Before Transarterial Radioembolization in Patients with Hepatocellular Carcinoma

Purpose

To identify disease-specific profiles comprising patient characteristics and imaging biomarkers on contrast-enhanced (CE)-computed tomography (CT) that enable the non-invasive prediction of the hepatopulmonary shunt fraction (HPSF) in patients with hepatocellular carcinoma (HCC) before resin-based transarterial radioembolization (TARE).

Patients and Methods

This institutional review board-approved (EA2/071/19) retrospective study included 56 patients with HCC recommended for TARE. All patients received tri-phasic CE-CT within 6 weeks prior to an angiographic TARE evaluation study using technetium-99m macroaggregated albumin. Imaging biomarkers representative of tumor extent, morphology, and perfusion, as well as disease-specific clinical parameters, were used to perform data-driven variable selection with backward elimination to generate multivariable linear regression models predictive of HPSF. Results were used to create clinically applicable risk scores for patients scheduled for TARE. Additionally, Cox regression was used to identify independent risk factors for poor overall survival (OS).

Results

Mean HPSF was 13.11% ± 7.6% (range: 2.8- 35.97%). Index tumor diameter (p = 0.014) or volume (p = 0.034) in combination with index tumor non-rim arterial phase enhancement (APHE) (p < 0.001) and washout (p < 0.001) were identified as significant non-invasive predictors of HPSF on CE-CT. Specifically, the prediction models revealed that the HPSF increased with index lesion diameter or volume and showed higher HPSF if non-rim APHE was present. In contrast, index tumor washout was associated with decreased HPSF levels. Independent risk factors of poorer OS were radiogenomic venous invasion and ascites at baseline.

Conclusion

The featured prediction models can be used for the initial non-invasive estimation of HPSF in patients with HCC before TARE to assist in clinical treatment evaluation while potentially sparing ineligible patients from the angiographic shunt evaluation study.

Comparison of PMT-based TF64 and SiPM-based Vereos PET/CT systems for 90 Y imaging and dosimetry optimization: A quantitative study

BACKGROUND

Selective internal radiotherapy based on transarterial radioembolization (TARE) with yttrium-90 (⁹⁰ Y) microspheres is an established treatment for primary or metastatic liver disease.

PURPOSE

The objective of this work is to optimize the dosimetry of patients treated with ⁹⁰ Y TARE, using positron emission tomography (PET) images.

METHODS

The NEMA 2012 PET phantom was filled with nearly 3.9 GBq of ⁹⁰ Y activity and acquired at days 0, 3, 5, 7, and 9 on a classic time-of-flight PET/computed tomography (CT) scanner (Philips TF64) and on a silicon photomultiplier (SiPM)-based PET/CT scanner (Philips Vereos). Acquisitions were carried on following the guidelines proposed in a previously published multicentric trial and images were reconstructed by varying and combining the available parameters. Comparisons were performed to identify the best set(s) of parameters leading to the most accurate ⁹⁰ Y-PET image(s), in terms of activity distribution. Then, for both scanners, the best images were analyzed with Simplicit⁹⁰ Y, a personalized dosimetry software using multicompartmental Medical Internal Radiation Dose model. The comparison between measured and true doses allowed to identify the image granting the most consistent dose estimations and, therefore, to designate the set of parameters to be applied on patients' data for the reconstruction of optimized clinical images. Posttreatment dosimetry of four patients was then realized with Simplicit⁹⁰ Y using optimized imaging datasets.

RESULTS

Based on activity distribution comparisons and dose estimations over phantom and patients data, the SiPM-based PET/CT system appeared more suitable than the photomultiplier tube-based TF64 for ⁹⁰ Y-PET imaging. With the SiPM-based PET/CT system, reconstructed images with a 2-mm voxel size combined with the application of the point spread function correction led to the most accurate results for quantitative ⁹⁰ Y measures.

CONCLUSIONS

For the SiPM-based PET/CT scanner, an optimized set of reconstruction parameters has been identified and applied on patients' data in order to generate the most accurate image to be used for an improved personalized ⁹⁰ Y-PET dosimetry, ensuring a reliable evaluation of the delivered doses.

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.

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.

Radioembolization for the Treatment of Hepatocellular Carcinoma: The Road to Personalized Dosimetry and Ablative Practice

Radioembolization dosimetry for the treatment of hepatocellular carcinoma has evolved alongside our understanding of best practice for this therapy. At the core of advances in dosimetry are personalized and ablative applications of radioembolization, which have generated paradigm shifts in both safety and efficacy. This review provides a summary of fundamental radioembolization dosimetry concepts and narrates how our approach to treating patients has shifted from conventional to tailored and definitive therapy.

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.

Metabolic activity assessment by 18 F-fluorodeoxyglucose positron emission tomography in patients with hepatocellular carcinoma undergoing Yttrium-90 transarterial radioembolization

BACKGROUND AND AIM

¹⁸ F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) is a functional image technique that can inform clinical decisions related to prognosis. We investigated the predictive role of ¹⁸ F-fluorodeoxyglucose PET/CT in patients with hepatocellular carcinoma (HCC) undergoing Yttrium-90 (Y-90) transarterial radioembolization (TARE).

METHODS

Patients with HCC treated with TARE and pre-TARE PET/CT scan were recruited between 2009 and 2013. Maximum standardized uptake value and tumor-to-non-tumorous liver uptake ratio (TLR) were measured. Tumor response was evaluated in accordance with modified RECIST criteria at 3-month intervals after Y-90 TARE.

RESULTS

Forty patients were included in the final analysis. The median age was 56.5 years and male predominant. Disease control in treated lesion was achieved in 82.5% (n = 33) of patients. During median 18.3-month follow-up, 27.5% (n = 11) of patients achieved progression-free survival. The cutoff of TLR, which was related to the median value, did not affect disease control rate, progression-free survival, and overall survival in patients with Y-90 TARE.

CONCLUSIONS

The TLR-based stratification may be a simple method, but our study did not show the usefulness in predicting prognosis in HCC patients with Y-90 TARE. Further studies with large number of patients are needed.

International recommendations for personalised selective internal radiation therapy of primary and metastatic liver diseases with yttrium-90 resin microspheres

PURPOSE

A multidisciplinary expert panel convened to formulate state-of-the-art recommendations for optimisation of selective internal radiation therapy (SIRT) with yttrium-90 (90Y)-resin microspheres.

METHODS

A steering committee of 23 international experts representing all participating specialties formulated recommendations for SIRT with 90Y-resin microspheres activity prescription and post-treatment dosimetry, based on literature searches and the responses to a 61-question survey that was completed by 43 leading experts (including the steering committee members). The survey was validated by the steering committee and completed anonymously. In a face-to-face meeting, the results of the survey were presented and discussed. Recommendations were derived and level of agreement defined (strong agreement ≥ 80%, moderate agreement 50%-79%, no agreement ≤ 49%).

RESULTS

Forty-seven recommendations were established, including guidance such as a multidisciplinary team should define treatment strategy and therapeutic intent (strong agreement); 3D imaging with CT and an angiography with cone-beam-CT, if available, and 99mTc-MAA SPECT/CT are recommended for extrahepatic/intrahepatic deposition assessment, treatment field definition and calculation of the 90Y-resin microspheres activity needed (moderate/strong agreement). A personalised approach, using dosimetry (partition model and/or voxel-based) is recommended for activity prescription, when either whole liver or selective, non-ablative or ablative SIRT is planned (strong agreement). A mean absorbed dose to non-tumoural liver of 40 Gy or less is considered safe (strong agreement). A minimum mean target-absorbed dose to tumour of 100-120 Gy is recommended for hepatocellular carcinoma, liver metastatic colorectal cancer and cholangiocarcinoma (moderate/strong agreement). Post-SIRT imaging for treatment verification with 90Y-PET/CT is recommended (strong agreement). Post-SIRT dosimetry is also recommended (strong agreement).

CONCLUSION

Practitioners are encouraged to work towards adoption of these recommendations.

To 1000 Gy and back again: a systematic review on dose-response evaluation in selective internal radiation therapy for primary and secondary liver cancer

Purpose

To systematically review all current evidence into the dose-response relation of yttrium-90 and holmium-166 selective internal radiation therapy (SIRT) in primary and secondary liver cancer.

Methods

A standardized search was performed in PubMed (MEDLINE), Embase, and the Cochrane Library in order to identify all published articles on dose-response evaluation in SIRT. In order to limit the results, all articles that investigated SIRT in combination with other therapy modalities (such as chemotherapy) were excluded.

Results

A total of 3038 records were identified of which 487 were screened based on the full text. Ultimately, 37 studies were included for narrative analysis. Meta-analysis could not be performed due to the large heterogeneity in study and reporting designs. Out of 37 studies, 30 reported a ‘mean dose threshold’ that needs to be achieved in order to expect a response. This threshold appears to be higher for hepatocellular carcinoma (HCC, 100–250 Gy) than for colorectal cancer metastases (CRC, 40–60 Gy). Reported thresholds tend to be lower for resin microspheres than when glass microspheres are used.

Conclusion

Although the existing evidence demonstrates a dose-response relationship in SIRT for both primary liver tumours and liver metastases, many pieces of the puzzle are still missing, hampering the definition of standardized dose thresholds. Nonetheless, most current evidence points towards a target mean dose of 100–250 Gy for HCC and 40–60 Gy for CRC. The field would greatly benefit from a reporting standard and prospective studies designed to elucidate the dose-response relation in different tumour types.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05340-0.

Impact of contouring methods on pre-treatment and post-treatment dosimetry for the prediction of tumor control and survival in HCC patients treated with selective internal radiation therapy

INTRODUCTION

The aim of this study was to evaluate the impact of the contouring methods on dose metrics and their predictive value on tumor control and survival, in both situations of pre-treatment and post-treatment dosimetry, for patients with advanced HCC treated with SIRT.

METHODS

Forty-eight patients who underwent SIRT between 2012 and 2020 were retrospectively included in this study. Target volumes were delineated using two methods: MRI-based contours manually drawn by a radiologist and then registered on SPECT/CT and PET/CT via deformable registration (Pre-C_MRI and Post-C_MRI), ^99mTc-MAA-SPECT and ⁹⁰Y-microspheres-PET 10% threshold contouring (Pre-C_SPECT and Post-C_PET). The mean absorbed dose (Dm) and the minimal absorbed dose delivered to 70% of the tumor volume (D70) were evaluated with both contouring methods; the tumor-to-normal liver uptake ratio (TNR) was evaluated with MRI-based contours only. Tumor response was assessed using the mRECIST criteria on the follow-up MRIs.

RESULTS

No significant differences were found for Dm and TNR between pre- and post-treatment. TNR evaluated with radiologic contours (Pre-C_MRI and Post-C_MRI) were predictive of tumor control at 6 months on pre- and post-treatment dosimetry (OR 5.9 and 7.1, respectively; p = 0.02 and 0.01). All dose metrics determined with both methods were predictive of overall survival (OS) on pre-treatment dosimetry, but only Dm with MRI-based contours was predictive of OS on post-treatment images with a median of 23 months for patients with a supramedian Dm versus 14 months for the others (p = 0.04).

CONCLUSION

In advanced HCC treated with SIRT, Dm and TNR determined with radiologic contours were predictive of tumor control and OS. This study shows that a rigorous clinical workflow (radiologic contours + registration on scintigraphic images) is feasible and should be prospectively considered for improving therapeutic strategy.

Diagnostic and prognostic value of 99mTc-MAA SPECT/CT for treatment planning of 90Y-resin microsphere radioembolization for hepatocellular carcinoma: comparison with planar image

^99mTc-macroaggregated albumin (MAA) imaging is performed before transarterial radioembolization (TARE), in which SPECT/CT is presumed more precise than planar image. However, additive role of SPECT/CT has not been well established. Thirty-four consecutive hepatocellular carcinoma patients of intermediate and advanced stages who underwent ⁹⁰Y-microsphere TARE were recruited. On pre-treatment planning scan using ^99mTc-MAA, image characteristics and absorbed dose for target tumors calculated by partition model methods were estimated on planar image and SPECT/CT, respectively. The measurements were repeated on post-treatment ⁹⁰Y PET/CT, as the reference standard. Treatment response was assessed and predictive values of image parameters were analyzed. The image characteristics including heterogeneity, necrosis and thrombosis uptake were better delineated on SPECT/CT than planar scan. The agreement and correlation of TNr between SPECT/CT and PET/CT were stronger than those between planar scan and PET/CT. Tumor dose estimated on ^99mTc-MAA SPECT/CT was more effective than planar image for prediction of treatment response, with cutoff value 125 Gy (sensitivity of 86% and specificity of 75%). In conclusion, ^99mTc-MAA SPECT/CT is more closely correlated with post-treatment ⁹⁰Y PET/CT, and is more effective for predicting treatment response than planar scan. SPECT/CT is superior to planar image in simulation before ⁹⁰Y TARE.

IPEM topical report: current molecular radiotherapy service provision and guidance on the implications of setting up a dosimetry service

Despite a growth in molecular radiotherapy treatment (MRT) and an increase in interest, centres still rarely perform MRT dosimetry. The aims of this report were to assess the main reasons why centres are not performing MRT dosimetry and provide advice on the resources required to set-up such a service. A survey based in the United Kingdom was developed to establish how many centres provide an MRT dosimetry service and the main reasons why it is not commonly performed. Twenty-eight per cent of the centres who responded to the survey performed some form of dosimetry, with 88% of those centres performing internal dosimetry. The survey showed that a 'lack of clinical evidence', a 'lack of guidelines' and 'not current UK practice' were the largest obstacles to setting up an MRT dosimetry service. More practical considerations, such as 'lack of software' and 'lack of staff training/expertise', were considered to be of lower significance by the respondents. Following on from the survey, this report gives an overview of the current guidelines, and the evidence available demonstrating the benefits of performing MRT dosimetry. The resources required to perform such techniques are detailed with reference to guidelines, training resources and currently available software. It is hoped that the information presented in this report will allow MRT dosimetry to be performed more frequently and in more centres, both in routine clinical practice and in multicentre trials. Such trials are required to harmonise dosimetry techniques between centres, build on the current evidence base, and provide the data necessary to establish the dose-response relationship for MRT.

Monte Carlo 90Y PET/CT dosimetry of unexpected focal radiation-induced lung damage after hepatic radioembolisation

Transarterial radioembolization (TARE) with ⁹⁰Y-loaded microspheres is an established therapeutic option for inoperable hepatic tumors. Increasing knowledge regarding TARE hepatic dose-response and dose-toxicity correlation is available but few studies have investigated dose-toxicity correlation in extra-hepatic tissues. We investigated absorbed dose levels for the appearance of focal lung damage in a case of off-target deposition of ⁹⁰Y microspheres and compared them with the corresponding thresholds recommended to avoiding radiation induced lung injury following TARE. A 64-year-old male patient received 1.6 GBq of ⁹⁰Y-labelled glass microspheres for an inoperable left lobe hepatocellular carcinoma. A focal off-target accumulation of radiolabeled microspheres was detected in the left lung upper lobe at the post-treatment ⁹⁰Y-PET/CT, corresponding to a radiation-induced inflammatory lung lesion at the 3-months ¹⁸F-FDG PET/CT follow-up. ⁹⁰Y-PET/CT data were used as input for Monte-Carlo based absorbed dose estimations. Dose-volume-histograms were computed to characterize the heterogeneity of absorbed dose distribution. The dose level associated with the appearance of lung tissue damage was estimated as the median absorbed dose measured at the edge of the inflammatory nodule. To account for respiratory movements and possible inaccuracy of image co-registration, three different methods were evaluated to define the irradiated off-target volume. Monte Carlo-derived absorbed dose distribution showed a highly heterogeneous absorbed dose pattern at the site of incidental microsphere deposition (volume = 2.13 ml) with a maximum dose of 630 Gy. Absorbed dose levels ranging from 119 Gy to 133 Gy, were estimated at the edge of the inflammatory nodule, depending on the procedure used to define the target volume. This report describes an original Monte Carlo based patient-specific dosimetry methodology for the study of the radiation-induced damage in a focal lung lesion after TARE. In our patient, radiation-induced focal lung damage occurred at significantly higher absorbed doses than those considered for single administration or cumulative lung dose delivered during TARE.

Planning dosimetry for 90 Y radioembolization with glass microspheres: Evaluating the fidelity of 99m Tc-MAA and partition model predictions

PURPOSE

^99m Tc-MAA-SPECT/CT may be used in ⁹⁰ Y-glass microsphere radioembolization treatment planning to assess perfused liver volumes and absorbed dose distributions. The partition model (PM) offers a more detailed planning dosimetry option beyond the single-compartment model more traditionally used in ⁹⁰ Y radioembolization. As ⁹⁰ Y radioembolization treatments shift toward activities and doses that aim to achieve tumor control, accurate and reliable treatment planning dosimetry for both tumors and normal liver (NL) becomes more critical. In this work, we explore the accuracy and precision of ⁹⁰ Y dosimetry predictions from pretherapy ^99m Tc-MAA and PM.

METHODS

Both PM and voxel dosimetry models were used to calculate tumor and NL mean doses using both planning ^99m Tc-MAA and verification ⁹⁰ Y-SPECT/CT in this retrospective analysis of hepatocellular carcinoma cases treated with glass microspheres (NCT01900002, n = 32). Linear regression models were developed at first access, and then later correct, the estimates by (a) ^99m Tc-MAA for ⁹⁰ Y voxel dosimetry and (b) ^99m Tc-MAA PM for voxel dosimetry, separately for both tumors and NL. Bland-Altman analysis was then used to evaluate the accuracy and precision of the regression model predictions with the mean bias and 95% prediction intervals (PI, ±1.96σ). Two categories of cases were stratified (catheter matched vs catheter unmatched) by establishing the level of ^99m Tc-MAA and ⁹⁰ Y catheter position alignment. Only catheter-matched cases were included in the ^99m Tc-MAA vs ⁹⁰ Y voxel dosimetry comparison, while all cases were used to compare dosimetry models (PM vs voxel).

RESULTS

Half (16/32) of cases were deemed catheter matched. ^99m Tc-MAA could reliably predict NL doses in catheter-matched cases after application of the linear model, with mean bias (PI) of -1% (±31%). PM was equivalent to voxel dosimetry for NL doses with mean bias (PI) of 0% (±1%). Even among catheter-matched cases, ^99m Tc-MAA planning for ⁹⁰ Y tumor voxel doses was poor, overestimating dose by an average of nearly 40%. Upon application of the linear model, ^99m Tc-MAA predictions for ⁹⁰ Y tumor voxel dose were only minimally biased (-4%) but possessed very large PI (±104%). PM predictions for tumor voxel dose using the linear model also showed small bias (-6%) but maintained similarly high PI of ±90%. Cases with tumors representing a large majority (>80%) of the total tumor volume demonstrated the best scenarios for ^99m Tc-MAA and PM tumor dose predictions, with mean biases (PI) of -3% (±53%) and -4% (±21%), respectively.

CONCLUSION

The unconditional use of ^99m Tc-MAA to predict ⁹⁰ Y dosimetry across all cases is not recommended due to: (a) demonstrated the risk of unmatched catheter positions between procedures, and (b) large bias and uncertainty in ^99m Tc-MAA predictions in cases with matched catheter locations. However, NL voxel dose predictions with ^99m Tc-MAA are clinically viable and either PM or voxel dosimetry can be used to produce equivalent predictions. Both ^99m Tc-MAA and PM can provide tumor dose predictions with potential clinical utility, but only in catheter-matched cases and with tumors comprising a clear majority (>80%) of the total tumor volume. These findings stratify the predictive fidelity of ^99m Tc-MAA- and PM-based treatment planning for ⁹⁰ Y dosimetry in improving treatment outcomes.

Transarterial Radioembolization for Hepatocellular Carcinoma and Hepatic Metastases: Clinical Aspects and Dosimetry Models

Transarterial radioembolization (TARE) with Yttrium-90 (⁹⁰Y) microspheres is a liver-directed therapy for primary and metastatic disease. This manuscript provides a review of the clinical literature on TARE indications and efficacy with overviews of patient-selection and toxicity. Current dosimetry models used in practice are safe, relatively simple, and easy for clinicians to use. Planning currently relies on the imperfect surrogate, ^99mTc macroaggregated albumin. Post-therapy quantitative imaging (⁹⁰Y SPECT/CT or ⁹⁰Y PET/CT) of microspheres can be used to calculate the macroscopic in vivo absorbed dose distribution. Similar to the evolution of other brachytherapy dose calculations, TARE is moving toward more patient-specific dosimetry that includes calculating and reporting nonuniform dose distributions throughout tumors and normal uninvolved liver.

Inter-observer variability of 90Y PET/CT dosimetry in hepatocellular carcinoma after glass microspheres transarterial radioembolization

INTRODUCTION

Strong correlation has been demonstrated between tumor dose and response and between healthy liver dose and side effects. Individualized dosimetry is increasingly recommended in the current clinical routine. However, hepatic and tumor segmentations could be complex in some cases. The aim of this study is to assess the reproducibility of the tumoral and non-tumoral liver dosimetry in selective internal radiation therapy (SIRT).

MATERIAL AND METHODS

Twenty-three patients with hepatocellular carcinoma (HCC) who underwent SIRT with glass microspheres were retrospectively included in the study. Tumor (TV) and total liver volumes (TLV), and mean absorbed doses in tumoral liver (TD) and non-tumoral liver (THLD) were determined on the ⁹⁰Y PET/CT studies using Simplicit90YTM software, by three independent observers. Dosimetry datasets were obtained by a medical physicist helped by a nuclear medicine (NM) physician with 10 years of experience (A), by a NM physician with 4-year experience (B), and by a resident who first performed 10 dosimetry assessments as a training (C). Inter-observer agreement was evaluated using intra-class correlation coefficients (ICC), coefficients of variation (CV), Bland-Altman plots, and reproducibility coefficient (RDC).

RESULTS

A strong agreement was observed between all three readers for estimating TLV (ICC 0.98) and THLD (ICC 0.97). Agreement was lower for TV delineation (ICC 0.94) and particularly for TD (ICC 0.73), especially for the highest values. Regarding TD, the CV (%) was 26.5, 26.9, and 20.2 between observers A and B, A and C, and B and C, respectively, and the RDC was 1.5. Regarding THLD, it was 8.5, 12.7, and 9.4, and the RDC was 1.3.

CONCLUSION

Using a standardized methodology, and regardless of the different experiences of the observers, the estimation of THLD is highly reproducible. Although the reproducibility of the assessment of tumor irradiation is overall quite high, large variations may be observed in a limited number of patients.

Radioembolization for the Treatment of Primary and Metastatic Liver Cancers

Radioembolization using ⁹⁰Y microspheres (glass or resin) has been introduced as an effective intraarterial therapy for unresectable primary and metastatic liver cancers. Although the basic therapeutic effect of chemoembolization results from ischemia, the therapeutic efficacy of radioembolization comes from radiation. Furthermore, compared with surgical resection and local ablation therapy, radioembolization is available with less limitation on the sites or number of liver cancers. The radioisotope ⁹⁰Y is a β-radiation emitter without γ-radiation, with the emission of secondary bremsstrahlung photons and small numbers of positrons. Administration of ⁹⁰Y microspheres into the hepatic artery can deliver a high dose of radiation selectively to the target tumor with limited radiation exposure to the surrounding normal parenchyma, and has low systemic toxicity. In general, radioembolization has been considered for patients with unresectable primary or metastatic liver-only or liver-dominant cancers with no ascites or other clinical signs of liver failure, life expectancy of > 12 weeks, and good performance status. Here, we review the current radioactive compounds, pretreatment assessment, and indications for radioembolization in patients with hepatocellular carcinoma, intrahepatic cholangiocarcinoma, and liver metastases from colorectal cancer.

Metastatic appendiceal cancer treated with Yttrium 90 radioembolization and systemic chemotherapy: A case report

BACKGROUND

Primary appendiceal cancers are rare, and they generally present with liver and/or peritoneal metastases. Currently there are no guidelines to treat metastatic appendiceal cancer, and hence they are treated as metastatic colorectal cancer. Combining Yttrium 90 (Y-90) radioembolization (RE) with systemic chemotherapy early in the treatment of right sided colon cancers has been shown to improve survival. Based on this data, a combination of systemic chemotherapy and Y-90 RE was used to treat a case of metastatic appendiceal cancer.

CASE SUMMARY

A 76-year-old male presented to the emergency room with progressive right lower quadrant pain. A Computed Tomography of the abdomen and pelvis was performed which showed acute appendicitis and contained perforation. Urgent laparoscopic appendectomy was then followed by histological analysis, which was significant for appendiceal adenocarcinoma. After complete workup he underwent right hemicolectomy and lymph node dissection. He received adjuvant chemotherapy as the local lymph nodes were positive. Follow-up imaging was significant for liver metastasis. Due to rapid growth of the liver lesions and new peritoneal nodules, the patient was treated with a combination of Y-90 RE and folinic acid, fluorouracil, and irinotecan with bevacizumab and not microwave ablation as previously planned. Follow up imaging demonstrated complete response of the liver lesions. At 12-mo follow-up, the patient continued to enjoy good quality of life with no recurrent disease.

CONCLUSION

Utilization of Y-90 RE concomitantly with systemic chemotherapy early in the treatment of appendiceal cancer may provide improved control of this otherwise aggressive cancer.

Safety and efficacy of radioembolization with glass microspheres in hepatocellular carcinoma patients with elevated lung shunt fraction: analysis of a 103-patient cohort

BACKGROUND

Technetium-99m macroaggregated albumin is used to estimate lung shunt fraction (LSF) prior to yttrium-90 (Y90). Studies have debated the safety and efficacy of Y90 in patients with LSF > 15%. We aimed to assess the role of Y90 in hepatocellular carcinoma (HCC) with LSF > 15%.

METHODS

With IRB approval, we searched our prospectively acquired database of HCC patients with Y90 treated with LSF > 15%. Median LSF and liver and lung doses were calculated. The response was assessed using RECIST. Overall survival (OS) was calculated from date of first Y90.

RESULTS

A total of 103 HCC patients underwent Y90. The median baseline LSF was 24.4% (IQR 18.1-28.8). Patients exhibited multifocal disease (59/103, 60%) and median tumor size of 7.85 cm (IQR 5.2, 10.57). BCLC class was A, B, C, and D in 7 (7%), 5 (5%), 85 (83%), and 6 (6%) patients, respectively. The median liver dose was 84.6 Gy (IQR 57.4, 107.55). The median lung dose per session and cumulatively was 22.9 Gy (IQR 15-28) and 29.5 Gy (IQR 20.5-44.3). Thirty-three patients (32%) demonstrated partial response, 57 stable disease, and 13 (13%) had progressive disease. The median OS was 7.3 months (95% CI 5.3, 11.47). Twenty patients (19%) had non-specific pulmonary symptoms (cough, shortness of breath, wheezing) in the 1-year post-Y90. The median time to the appearance of non-specific pulmonary symptoms was 63 days (range 7-224). Thoracic imaging demonstrated no pulmonary fibrosis/injury following treatment in any patient.

CONCLUSION

Y90 can be performed in patients with LSF > 15%. The RECIST response was identified in 32% of the patients. In isolation, LSF > 15% should not deter from treatment with Y90.

Comparative dosimetry between 99mTc-MAA SPECT/CT and 90Y PET/CT in primary and metastatic liver tumors

INTRODUCTION

The aim of this study is to determine whether ^99mTc-MAA SPECT/CT-based dosimetry could predict the actual absorbed dose in hepatocellular carcinoma (HCC) or liver metastases, treated by glass or resin microspheres.

MATERIAL AND METHODS

Fifty-seven patients who underwent selective internal radiation therapy (SIRT) were retrospectively included in the study, for a total of 59 treatments. Nineteen HCC were treated by resin microspheres (HCC-SIR), 20 HCC with glass microspheres (HCC-Thera), and 20 liver metastases with resin microspheres (Metastases-SIR). The mean absorbed doses in tumoral liver (Dm) and non-tumoral liver (DmNTL) were determined on the ^99mTc-MAA SPECT/CT and the ⁹⁰Y PET/CT, and compared with each other.

RESULTS

DmNTL was < 50 Gy in the 3 groups, with a strong correlation in all population, albeit slightly lower in Metastases-SIR than HCC-SIR and HCC-Thera (CCC 0.8, 0.94 and 0.96, respectively). In tumoral liver, Dm was higher in HCC than metastases (159 ± 117 Gy versus 63 ± 31 Gy). ^99mTc-MAA SPECT/CT proved to be a better indicator of Dm in HCC compared with metastases, with similar ^99mTc-MAA-⁹⁰Y concordance in resin and glass microspheres (CCC HCC-SIR 0.82, CCC HCC-Thera 0.82, and CCC Metastases-SIR 0.52).

CONCLUSION

^99mTc-MAA SPECT/CT is a reasonably reliable tool for predicting the dose to the non-tumoral liver in both HCC and metastases, regardless of the type of microspheres. It is also fairly reliable for predicting the tumor dose in HCC, again regardless of the type of spheres, although individual variations are observed.

The value of 99mTc-MAA SPECT/CT for lung shunt estimation in 90Y radioembolization: a phantom and patient study

Background

A major toxicity concern in radioembolization therapy of hepatic malignancies is radiation-induced pneumonitis and sclerosis due to hepatopulmonary shunting of ⁹⁰Y microspheres. Currently, ^99mTc macroaggregated albumin (^99mTc-MAA) imaging is used to estimate the lung shunt fraction (LSF) prior to treatment. The aim of this study was to evaluate the accuracy/precision of LSF estimated from ^99mTc planar and SPECT/CT phantom imaging, and within this context, to compare the corresponding LSF and lung-absorbed dose values from ^99mTc-MAA patient studies. Additionally, LSFs from pre- and post-therapy imaging were compared.

Results

A liver/lung torso phantom filled with ^99mTc to achieve three lung shunt values was scanned by planar and SPECT/CT imaging with repeat acquisitions to assess accuracy and precision. To facilitate processing of patient data, a workflow that relies on SPECT and CT-based auto-contouring to define liver and lung volumes for the LSF calculation was implemented. Planar imaging-based LSF estimates for 40 patients, obtained from their medical records, were retrospectively compared with SPECT/CT imaging-based calculations with attenuation and scatter correction. Additionally, in a subset of 20 patients, the pre-therapy estimates were compared with ⁹⁰Y PET/CT-based measurements.

In the phantom study, improved accuracy in LSF estimation was achieved using SPECT/CT with attenuation and scatter correction (within 13% of the true value) compared with planar imaging (up to 44% overestimation). The results in patients showed a similar trend with planar imaging significantly overestimating LSF compared to SPECT/CT. There was no correlation between lung shunt estimates and the delay between ^99mTc-MAA administration and scanning, but off-target extra hepatic uptake tended to be more likely in patients with a longer delay. The mean lung absorbed dose predictions for the 28 patients who underwent therapy was 9.3 Gy (range 1.3–29.4) for planar imaging and 3.2 Gy (range 0.4–13.4) for SPECT/CT. For the patients with post-therapy imaging, the mean LSF from ⁹⁰Y PET/CT was 1.0%, (range 0.3–2.8). This value was not significantly different from the mean LSF estimate from ^99mTc-MAA SPECT/CT (mean 1.0%, range 0.4–1.6; p = 0.968), but was significantly lower than the mean LSF estimate based on planar imaging (mean 4.1%, range 1.2–15.0; p = 0.0002).

Conclusions

The improved accuracy demonstrated by the phantom study, agreement with ⁹⁰Y PET/CT in patient studies, and the practicality of using auto-contouring for liver/lung definition suggests that ^99mTc-MAA SPECT/CT with scatter and attenuation corrections should be used for lung shunt estimation prior to radioembolization.

The effect of selective internal radiation therapy with yttrium-90 resin microspheres on lung carbon monoxide diffusion capacity

Background

Selective internal radiation therapy (SIRT) with embolization of branches of the hepatic artery is a valuable therapeutic tool for patients with hepatic malignancies; however, it is also associated with lung injury risk due to shunting. Diffusion capacity of the lungs for carbon monoxide (DLCO) is a clinically significant lung function test, and worsening in DLCO is suggested to reflect a limited gas exchange reserve caused by the potential toxicity of chemoradiotherapy or it may be a marker of related lung injury. This study aimed to examine the changes in DLCO during SIRT with resin microspheres in newly treated and retreated patients. Forty consecutive patients who received SIRT for a variety of malignant conditions were included. All subjects were treated with Yttrium-90 labelled resin microspheres. DLCO tests were performed after the procedures. In addition, patients were specifically followed for radiation pneumonitis.

Results

The mean DLCO did not significantly change after the first (82.8 ± 19.4 vs. 83.1 ± 20.9, p = 0.921) and the second treatments (87.4 ± 19.7 vs. 88.6 ± 23.2, p = 0.256). Proportion of patients with impaired DLCO at baseline was not altered significantly after the first (37.5 vs. 45.0%, p = 0.581) and the second treatments (27.3 vs. 27.3%, p = 1.000). Also, percent change in DLCO values did not correlate with radiation dose, lung shunt fraction, or lung exposure dose (p > 0.05 for all comparisons). None of the patients developed radiation pneumonitis.

Conclusions

Our results suggest that no significant change in DLCO in association with SIRT occurs, both after the first or the second treatment sessions. Further larger studies possibly with different protocols are warranted to better delineate DLCO changes after SIRT in a larger spectrum of patients.

Estimation of lung shunt fraction from simultaneous fluoroscopic and nuclear images

Radioembolisation with yttrium-90 (⁹⁰Y) is increasingly used as a treatment of unresectable liver malignancies. For safety, a scout dose of technetium-99m macroaggregated albumin (^99mTc-MAA) is used prior to the delivery of the therapeutic activity to mimic the deposition of ⁹⁰Y. One-day procedures are currently limited by the lack of nuclear images in the intervention room. To cope with this limitation, an interventional simultaneous fluoroscopic and nuclear imaging device is currently being developed. The purpose of this simulation study was to evaluate the accuracy of estimating the lung shunt fraction (LSF) of the scout dose in the intervention room with this device and compare it against current clinical methods.

METHODS

A male and female XCAT phantom, both with two respiratory profiles, were used to simulate various LSFs resulting from a scout dose of 150 MBq ^99mTc-MAA. Hybrid images were Monte Carlo simulated for breath-hold (5 s) and dynamic breathing (10 frames of 0.5 s) acquisitions. Nuclear images were corrected for attenuation with the fluoroscopic image and for organ overlap effects using a pre-treatment CT-scan. For comparison purposes, planar scintigraphy and mobile gamma camera images (both 300 s acquisition time) were simulated. Estimated LSFs were evaluated for all methods and compared to the phantom ground truth.

RESULTS

In the clinically relevant range of 10-20% LSF, hybrid imaging overestimated LSF with approximately 2 percentage points (pp) and 3 pp for the normal and irregular breathing phantoms, respectively. After organ overlap correction, LSF was estimated with a more constant error. Errors in planar scintigraphy and mobile gamma camera imaging were more dependent on LSF, body shape and breathing profile.

CONCLUSION

LSF can be estimated with a constant minor error with a hybrid imaging device. Estimated LSF is highly dependent on true LSF, body shape and breathing pattern when estimated with current clinical methods. The hybrid imaging device is capable of accurately estimating LSF within a few seconds in an interventional setting.

Treating hepatocellular carcinoma with 90Y-bearing microspheres: a review

Hepatocellular carcinoma (HCC) is a disease usually diagnosed in its advanced-stage, and is frequently not amenable to curative surgical treatment. Also, HCC is resistant to chemotherapy and less vulnerable to radiation therapy compared to normal hepatic parenchyma. Both of these facts render the efficacy of adjuvant and palliative treatments problematic. Selective internal radiation therapy (SIRT) with ⁹⁰Y-bearing microspheres is characterized by preferentially delivering substantially high doses of radiation to a liver tumor dose simultaneously limiting the damage to its non-tumorous cells, providing an opportunity for effective local tumor control and even tumor regression therapy. The current article reviews the specific characters, dosimetry, possible applications, and special considerations toward the pre-existing radiation therapy of ⁹⁰Y microsphere SIRT in treating HCC.

Transarterial radioembolization for hepatocellular carcinoma: a review

Hepatocellular carcinoma (HCC) is the most common type of liver cancer and is the second cause of death due to malignancy in the world. The treatment of HCC is complex and includes potentially curative and palliative approaches. However, both curative and palliative treatments for HCC are often associated with a not-completely favorable safety/efficacy ratio. Therefore, other treatment options appear necessary in clinical practice. Transarterial radioembolization has shown a promising efficacy in terms of disease control and is associated with a good safety profile. This review discusses the use of transarterial radioembolization in HCC, with a focus on the clinical aspects of this therapeutic strategy.

Transarterial chemoembolization versus transarterial radioembolization in hepatocellular carcinoma: optimization of selecting treatment modality

Hepatocellular carcinoma (HCC) of intermediate stage consists of diverse tumor and patient factors in terms of tumor number, size and liver function resulting in various outcomes given by transarterial chemoembolization (TACE). Transarterial radioembolization (TARE) using radioactive isotope, β-ray emitting Yttrium-90 with a short half-life and penetration depth, is an emerging intra-arterial brachytherapy characterized by potent anti-cancer effect given by radiation but minimal embolic effect. Although there is lack of study directly comparing the efficacy and safety between TACE and TARE in patients with unresectable HCC, several retrospective or small-scaled studies suggest that overall efficacy indicated by overall survival and time to progression is similar between two modalities and TARE has a superiority in the safety including postembolization syndrome, hospitalization days and outpatient-based therapy. In advanced HCC with portal vein (PV) invasion, TACE is not consistently recommended due to risk of hepatic decompensation or failure after procedure. On the contrary, available data suggest that TARE might be a promising treatment option in HCC with PV thrombosis if patient's liver function is preserved and the level of PV invasion is less than main trunk. Ongoing trials comparing TARE and sorafenib in advanced HCC would elucidate the role of this locoregional therapy. The need of a multidisciplinary team, complex steps of procedure and high cost of TARE are the hurdles to widespread recommendation of this therapy in intermediate or advanced HCC. The optimization of selection between TACE and TARE might be dependent on availability, experience, tumor factors and patient factors.

Semi-Quantitative Analysis of Post-Transarterial Radioembolization (90)Y Microsphere Positron Emission Tomography Combined with Computed Tomography (PET/CT) Images in Advanced Liver Malignancy: Comparison With (99m)Tc Macroaggregated Albumin (MAA) Single Photon Emission Computed Tomography (SPECT)

OBJECTIVES

The purpose of this study is to evaluate the correlation between pretreatment planning technetium-99m ((99m)Tc) macroaggregated albumin (MAA) SPECT images and posttreatment transarterial radioembolization (TARE) yttirum-90 ((90)Y) PET/CT images by comparing the ratios of tumor-to-normal liver counts.

METHODS

Fifty-two patients with advanced hepatic malignancy who underwent (90)Y microsphere radioembolization from January 2010 to December 2012 were retrospectively reviewed. Patients had undergone (99m)Tc MAA intraarterial injection SPECT for a pretreatment evaluation of microsphere distribution and therapy planning. After the administration of (90)Y microspheres, the patients underwent posttreatment (90)Y PET/CT within 24 h. For semiquantitative analysis, the tumor-to-normal uptake ratios in (90)Y PET/CT (TNR-yp) and (99m)Tc MAA SPECT (TNR-ms) as well as the tumor volumes measured in angiographic CT were obtained and analyzed. The relationship of TNR-yp and TNR-ms was evaluated by Spearman's rank correlation and Wilcoxon's matched pairs test.

RESULTS

In a total of 79 lesions of 52 patients, the distribution of microspheres was well demonstrated in both the SPECT and PET/CT images. A good correlation was observed of between TNR-ms and TNR-yp (rho value = 0.648, p < 0.001). The TNR-yp (median 2.78, interquartile range 2.43) tend to show significantly higher values than TNR-ms (median 2.49, interquartile range of 1.55) (p = 0.012). The TNR-yp showed weak correlation with tumor volume (rho = 0.230, p = 0.041).

CONCLUSIONS

The (99m)Tc MAA SPECT showed a good correlation with (90)Y PET/CT in TNR values, suggesting that (99m)Tc MAA can be used as an adequate pretreatment evaluation method. However, the (99m)Tc MAA SPECT image consistently shows lower TNR values compared to (90)Y PET/CT, which means the possibility of underestimation of tumorous uptake in the partition dosimetry model using (99m)Tc MAA SPECT. Considering that (99m)Tc MAA is the only clinically available surrogate marker for distribution of microsphere, we recommend measurement of tumorous uptake using (90)Y PET/CT should be included routinely in the posttherapeutic evaluation.

Clinical impact of (99m)Tc-MAA SPECT/CT-based dosimetry in the radioembolization of liver malignancies with (90)Y-loaded microspheres

Radioembolization with (90)Y-loaded microspheres is increasingly used in the treatment of primary and secondary liver cancer. Technetium-99 m macroaggregated albumin (MAA) scintigraphy is used as a surrogate of microsphere distribution to assess lung or digestive shunting prior to therapy, based on tumoral targeting and dosimetry. To date, this has been the sole pre-therapeutic tool available for such evaluation. Several dosimetric approaches have been described using both glass and resin microspheres in hepatocellular carcinoma (HCC) and liver metastasis. Given that each product offers different specific activities and numbers of spheres injected, their radiobiological properties are believed to lightly differ. This paper summarizes and discusses the available studies focused on MAA-based dosimetry, particularly concentrating on potential confounding factors like clinical context, tumor size, cirrhosis, previous or concomitant therapy, and product used. In terms of the impact of tumoral dose in HCC, the results were concordant and a response relationship and tumoral threshold dose was clearly identified, especially in studies using glass microspheres. Tumoral dose has also been found to influence survival. The concept of treatment intensification has recently been introduced, yet despite several studies publishing interesting findings on the tumor dose-metastasis relationship, no consensus has been reached, and further clarification is thus required. Nor has the maximal tolerated dose to the liver been well documented, requiring more accurate evaluation. Lung dose was well described, despite recently identified factors influencing its evaluation, requiring further assessment. Conclusion: MAA SPECT/CT dosimetry is accurate in HCC and can now be used in order to achieve a fully customized approach, including treatment intensification. Yet further studies are warranted for the metastasis setting and evaluating the maximal tolerated liver dose.

Trans-Arterial Radioembolization for Hepatocellular Carcinoma

This article offers an overview of a new therapeutic option in hepatocellular carcinoma using trans-arterial radioembolization. In particular, it covers practical aspects of the technique and the currently available preliminary data in terms of disease control. We explore the potentials of radioembolization both in early and advanced stages of the disease, as single treatment and as companion to targeted agents such as sorafenib.

Transarterial radioembolization for hepatocellular carcinoma: An update and perspectives

In the last decade trans-arterial radioembolization has given promising results in the treatment of patients with intermediate or advanced stage hepatocellular carcinoma (HCC), both in terms of disease control and tolerability profile. This technique consists of the selective intra-arterial administration of microspheres loaded with a radioactive compound (usually Yttrium(90)), and exerts its therapeutic effect through the radiation carried by these microspheres. A careful and meticulous selection of patients is crucial before performing the radioembolization to correctly perform the procedure and reduce the incidence of complications. Radioembolization is a technically complex and expensive technique, which has only recently entered clinical practice and is supported by scant results from phase III clinical trials. Nevertheless, it may represent a valid alternative to transarterial chemoembolization (TACE) in the treatment of intermediate-stage HCC patients, as shown by a comparative retrospective assessment that reported a longer time to progression, but not of overall survival, and a more favorable safety profile for radioembolization. In addition, this treatment has reported a higher percentage of tumor shrinkage, if compared to TACE, for pre-transplant downsizing and it represents a promising therapeutic option in patients with large extent of disease and insufficient residual liver volume who are not immediately eligible for surgery. Radioembolization might also be a suitable companion to sorafenib in advanced HCC or it can be used as a potential alternative to this treatment in patients who are not responding or do not tolerate sorafenib.

A review of 3D image-based dosimetry, technical considerations and emerging perspectives in 90Y microsphere therapy

Yttrium-90 radioembolization (⁹⁰Y-RE) is a well-established therapy for the treatment of hepatocellular carcinoma (HCC) and also of metastatic liver deposits from other malignancies. Nuclear Medicine and Cath Lab diagnostic imaging takes a pivotal role in the success of the treatment, and in order to fully exploit the efficacy of the technique and provide reliable quantitative dosimetry that are related to clinical endpoints in the era of personalized medicine, technical challenges in imaging need to be overcome. In this paper, the extensive literature of current ⁹⁰Y-RE techniques and challenges facing it in terms of quantification and dosimetry are reviewed, with a focus on the current generation of 3D dosimetry techniques. Finally, new emerging techniques are reviewed which seek to overcome these challenges, such as high-resolution imaging, novel surgical procedures and the use of other radiopharmaceuticals for therapy and pre-therapeutic planning.

Fusion dual-tracer SPECT-based hepatic dosimetry predicts outcome after radioembolization for a wide range of tumour cell types

Purpose

Fusion dual-tracer SPECT imaging enables physiological rather than morphological voxel-based partitioning and dosimetry for ⁹⁰Y hepatic radioembolization (RE). We evaluated its prognostic value in a large heterogeneous cohort of patients with extensive hepatic malignancy.

Methods

A total of 122 patients with primary or secondary liver malignancy (18 different cell types) underwent SPECT imaging after intraarterial injection of ^99mTc macroaggregated albumin (TcMAA) as a simulation of subsequent ⁹⁰Y microsphere distribution, followed by administration of an excess of intravenous ^99mTc-labelled sulphur colloid (TcSC) as a biomarker for functional liver, and a second SPECT scan. TcMAA distribution was used to estimate ⁹⁰Y radiation absorbed dose in tumour (D_T) and in functional liver. Laboratory and clinical follow-up were recorded for 12 weeks after RE, and radiographic responses according to (m)RECIST were evaluated at 3 and 6 months. Dose–response relationships were determined for efficacy and toxicity.

Results

Patients were treated with a median of 1.73 GBq activity of resin microspheres (98 patients) or glass microspheres (24 patients), in a whole-liver approach (97 patients) or a lobar approach (25 patients). The objective response rate was 41 % at 3 months and 48 % at 6 months. Response was correlated with D_T (P < 0.01). Median overall survival was 10.1 months (95 % confidence interval 7.4 – 12.8 months). Responders lived for 36.0 months compared to 8.7 months for nonresponders (P < 0.01). Stratified for tumour cell type, D_T was independently associated with survival (P < 0.01). Absorbed dose in functional liver was correlated with toxicity grade change (P < 0.05) and RE-induced liver disease (P < 0.05).

Conclusion

Fusion dual-tracer SPECT imaging offers a physiology-based functional imaging tool to predict efficacy and toxicity of RE. This technique can be refined to define dosing thresholds for specific tumour types and treatments, but appears generally predictive even in a heterogeneous cohort.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-015-3048-z) contains supplementary material, which is available to authorized users.

Radioembolization of hepatic lesions from a radiobiology and dosimetric perspective

Radioembolization (RE) of liver cancer with ⁹⁰Y-microspheres has been applied in the last two decades with notable responses and acceptable toxicity. Two types of microspheres are available, glass and resin, the main difference being the activity/sphere. Generally, administered activities are established by empirical methods and differ for the two types. Treatment planning based on dosimetry is a prerogative of few centers, but has notably gained interest, with evidence of predictive power of dosimetry on toxicity, lesion response, and overall survival (OS). Radiobiological correlations between absorbed doses and toxicity to organs at risk, and tumor response, have been obtained in many clinical studies. Dosimetry methods have evolved from the macroscopic approach at the organ level to voxel analysis, providing absorbed dose spatial distributions and dose–volume histograms (DVH). The well-known effects of the external beam radiation therapy (EBRT), such as the volume effect, underlying disease influence, cumulative damage in parallel organs, and different tolerability of re-treatment, have been observed also in RE, identifying in EBRT a foremost reference to compare with. The radiobiological models – normal tissue complication probability and tumor control probability – and/or the style (DVH concepts) used in EBRT are introduced in RE. Moreover, attention has been paid to the intrinsic different activity distribution of resin and glass spheres at the microscopic scale, with dosimetric and radiobiological consequences. Dedicated studies and mathematical models have developed this issue and explain some clinical evidences, e.g., the shift of dose to higher toxicity thresholds using glass as compared to resin spheres. This paper offers a comprehensive review of the literature incident to dosimetry and radiobiological issues in RE, with the aim to summarize the results and to identify the most useful methods and information that should accompany future studies.

Personalized predictive lung dosimetry by technetium-99m macroaggregated albumin SPECT/CT for yttrium-90 radioembolization

Background

For yttrium-90 (⁹⁰Y) radioembolization, the common practice of assuming a standard 1,000-g lung mass for predictive dosimetry is fundamentally incongruent with the modern philosophy of personalized medicine. We recently developed a technique of personalized predictive lung dosimetry using technetium-99m (^99mTc) macroaggregated albumin (MAA) single photon emission computed tomography with integrated CT (SPECT/CT) of the lung as part of our routine dosimetric protocol for ⁹⁰Y radioembolization. Its rationales are the technical superiority of SPECT/CT over planar scintigraphy, ease and convenience of lung auto-segmentation CT densitovolumetry, and dosimetric advantage of patient-specific lung parenchyma masses.

Methods

This is a retrospective study of our pulmonary clinical outcomes and comparison of lung dosimetric accuracy and precision by ^99mTc MAA SPECT/CT versus conventional planar methodology. ⁹⁰Y resin microspheres (SIR-Spheres) were used for radioembolization. Diagnostic CT densitovolumetry was used as a reference for lung parenchyma mass. Pulmonary outcomes were based on follow-up diagnostic CT chest or X-ray.

Results

Thirty patients were analyzed. The mean lung parenchyma mass of our Southeast Asian cohort was 822 ± 103 g standard deviation (95% confidence interval 785 to 859 g). Patient-specific lung parenchyma mass estimation by CT densitovolumetry on ^99mTc MAA SPECT/CT is accurate (bias −21.7 g) and moderately precise (95% limits of agreement −194.6 to +151.2 g). Lung mean radiation absorbed doses calculated by ^99mTc MAA SPECT/CT and planar methodology are both accurate (bias <0.5 Gy), but ^99mTc MAA SPECT/CT offers better precision over planar methodology (95% limits of agreement −1.76 to +2.40 Gy versus −3.48 to +3.31 Gy, respectively). None developed radiomicrosphere pneumonitis when treated up to a lung mean radiation absorbed dose of 18 Gy at a median follow-up of 4.4 months.

Conclusions

Personalized predictive lung dosimetry by ^99mTc MAA SPECT/CT is clinically feasible, safe, and more precise than conventional planar methodology for ⁹⁰Y radioembolization radiation planning.

Regional hepatic therapies: an important component in the management of colorectal cancer liver metastases

The treatment of colorectal cancer liver metastases (CRLM) has evolved significantly in the last 15 years. Currently, complete surgical resection remains the only potentially curative option; unfortunately, approximately 80% of patients with CRLM are not candidates for complete tumor resection. For patients with unresectable CRLM the available treatment options were historically limited; however, the development of regional hepatic therapies (RHT) and improvement of systemic chemotherapeutic regimens have emerged as viable options to improve overall survival and quality of life for this group of patients. The selection, sequence and integration of interventions into a multi-modal approach is a complex and evolving discipline. In this article, the currently available RHT modalities for CRLM are presented as a guide to the options for clinical treatment decisions.

Twelve-year experience of radioembolization for colorectal hepatic metastases in 214 patients: survival by era and chemotherapy

PURPOSE

The aim of this study was to analyze the safety, treatment characteristics and survival outcomes of Yttrium-90 (Y90) radioembolization for unresectable colorectal carcinoma (CRC) liver metastases refractory to standard of care therapy.

METHODS

A total of 214 patients with CRC metastases were treated with Y90 radioembolization over 12 years. Toxicity was assessed using National Cancer Institute common terminology criteria. Overall survival was analyzed from date of diagnosis of primary cancer, hepatic metastases and from the first Y90. Uni/multivariate analyses were performed. Substratification by era of chemotherapeutics was performed.

RESULTS

Most patients were male (60 %) and <65 years old (61 %). Of them, 98 % had been exposed to chemotherapy. Grade 3 lymphocyte, bilirubin, albumin, ALP and AST toxicities were observed in 39 %, 11 %, 10 %, 8 % and 4 % of patients, respectively. Grade 4 lymphocyte and ALP toxicities were observed in 5 % and 3 % of patients, respectively. Median overall survival was 43.0, 34.6, and 10.6 months from date of diagnosis of primary cancer, hepatic metastases and first Y90, respectively. Survival was significantly longer in patients: (1) who received ≤2 cytotoxic drugs (n = 104) than those who received 3 (n = 110) (15.2 vs. 7.5 months, p = 0.0001); and (2) who received no biologic agents (n = 52) compared with those that did (n = 162) (18.6 vs. 9.4 months, p = 0.0001). Multivariate analyses identified ≤2 cytotoxic agents, no exposure to biologics, ECOG 0, tumor burden <25 %, lack of extrahepatic disease and albumin >3 g/dL as independent predictors of survival.

CONCLUSION

In this largest metastatic CRC series published to date, Y90 radioembolization was found to be safe; survival varied by prior therapy. Further studies are required to further refine the role of Y90 in metastatic CRC.

(⁹⁹m)Tc-MAA overestimates the absorbed dose to the lungs in radioembolization: a quantitative evaluation in patients treated with ¹⁶⁶Ho-microspheres

PURPOSE

Radiation pneumonitis is a rare but serious complication of radioembolic therapy of liver tumours. Estimation of the mean absorbed dose to the lungs based on pretreatment diagnostic (99m)Tc-macroaggregated albumin ((99m)Tc-MAA) imaging should prevent this, with administered activities adjusted accordingly. The accuracy of (99m)Tc-MAA-based lung absorbed dose estimates was evaluated and compared to absorbed dose estimates based on pretreatment diagnostic (166)Ho-microsphere imaging and to the actual lung absorbed doses after (166)Ho radioembolization.

METHODS

This prospective clinical study included 14 patients with chemorefractory, unresectable liver metastases treated with (166)Ho radioembolization. (99m)Tc-MAA-based and (166)Ho-microsphere-based estimation of lung absorbed doses was performed on pretreatment diagnostic planar scintigraphic and SPECT/CT images. The clinical analysis was preceded by an anthropomorphic torso phantom study with simulated lung shunt fractions of 0 to 30 % to determine the accuracy of the image-based lung absorbed dose estimates after (166)Ho radioembolization.

RESULTS

In the phantom study, (166)Ho SPECT/CT-based lung absorbed dose estimates were more accurate (absolute error range 0.1 to -4.4 Gy) than (166)Ho planar scintigraphy-based lung absorbed dose estimates (absolute error range 9.5 to 12.1 Gy). Clinically, the actual median lung absorbed dose was 0.02 Gy (range 0.0 to 0.7 Gy) based on posttreatment (166)Ho-microsphere SPECT/CT imaging. Lung absorbed doses estimated on the basis of pretreatment diagnostic (166)Ho-microsphere SPECT/CT imaging (median 0.02 Gy, range 0.0 to 0.4 Gy) were significantly better predictors of the actual lung absorbed doses than doses estimated on the basis of (166)Ho-microsphere planar scintigraphy (median 10.4 Gy, range 4.0 to 17.3 Gy; p < 0.001), (99m)Tc-MAA SPECT/CT imaging (median 2.5 Gy, range 1.2 to 12.3 Gy; p < 0.001), and (99m)Tc-MAA planar scintigraphy (median 5.5 Gy, range 2.3 to 18.2 Gy; p < 0.001).

CONCLUSION

In clinical practice, lung absorbed doses are significantly overestimated by pretreatment diagnostic (99m)Tc-MAA imaging. Pretreatment diagnostic (166)Ho-microsphere SPECT/CT imaging accurately predicts lung absorbed doses after (166)Ho radioembolization.

Newer treatments for advanced hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide. The only curative treatment modalities for HCC are surgery, percutaneous ablation, and liver transplantation. Unfortunately, the majority of patients have unresectable disease at diagnosis. Therefore, effective treatment options are needed for patients with advanced HCC. The current standard treatment for patients with advanced HCC, according to the Barcelona Clinic Liver Cancer staging system, is the multikinase inhibitor sorafenib. Other alternative therapies are required, due to the limited treatment response to, and tolerance of, this molecular target agent. Clinical trials of hepatic artery infusion chemotherapy, radioembolization, and multimodal treatments have shown favorable results in advanced HCC patients. This article introduces new treatment modalities for advanced HCC and discusses future therapeutic possibilities.

Post-radioembolization yttrium-90 PET/CT - part 2: dose-response and tumor predictive dosimetry for resin microspheres

Background

Coincidence imaging of low-abundance yttrium-90 (⁹⁰Y) internal pair production by positron emission tomography with integrated computed tomography (PET/CT) achieves high-resolution imaging of post-radioembolization microsphere biodistribution. Part 2 analyzes tumor and non-target tissue dose-response by ⁹⁰Y PET quantification and evaluates the accuracy of tumor ^99mTc macroaggregated albumin (MAA) single-photon emission computed tomography with integrated CT (SPECT/CT) predictive dosimetry.

Methods

Retrospective dose quantification of ⁹⁰Y resin microspheres was performed on the same 23-patient data set in part 1. Phantom studies were performed to assure quantitative accuracy of our time-of-flight lutetium-yttrium-oxyorthosilicate system. Dose-responses were analyzed using ⁹⁰Y dose-volume histograms (DVHs) by PET voxel dosimetry or mean absorbed doses by Medical Internal Radiation Dose macrodosimetry, correlated to follow-up imaging or clinical findings. Intended tumor mean doses by predictive dosimetry were compared to doses by ⁹⁰Y PET.

Results

Phantom studies demonstrated near-perfect detector linearity and high tumor quantitative accuracy. For hepatocellular carcinomas, complete responses were generally achieved at D₇₀ > 100 Gy (D₇₀, minimum dose to 70% tumor volume), whereas incomplete responses were generally at D₇₀ < 100 Gy; smaller tumors (<80 cm³) achieved D₇₀ > 100 Gy more easily than larger tumors. There was complete response in a cholangiocarcinoma at D₇₀ 90 Gy and partial response in an adrenal gastrointestinal stromal tumor metastasis at D₇₀ 53 Gy. In two patients, a mean dose of 18 Gy to the stomach was asymptomatic, 49 Gy caused gastritis, 65 Gy caused ulceration, and 53 Gy caused duodenitis. In one patient, a bilateral kidney mean dose of 9 Gy (V₂₀ 8%) did not cause clinically relevant nephrotoxicity. Under near-ideal dosimetric conditions, there was excellent correlation between intended tumor mean doses by predictive dosimetry and those by ⁹⁰Y PET, with a low median relative error of +3.8% (95% confidence interval, -1.2% to +13.2%).

Conclusions

Tumor and non-target tissue absorbed dose quantification by ⁹⁰Y PET is accurate and yields radiobiologically meaningful dose-response information to guide adjuvant or mitigative action. Tumor ^99mTc MAA SPECT/CT predictive dosimetry is feasible. ⁹⁰Y DVHs may guide future techniques in predictive dosimetry.

Boosted selective internal radiation therapy with 90Y-loaded glass microspheres (B-SIRT) for hepatocellular carcinoma patients: a new personalized promising concept

PURPOSE

To evaluate the impact of dosimetry based on MAA SPECT/CT for the prediction of response, toxicity and survival, and for treatment planning in patients with hepatocellular carcinoma (HCC) treated with (90)Y-loaded glass microspheres (TheraSphere®).

METHODS

TheraSphere® was administered to 71 patients with inoperable HCC. MAA SPECT/CT quantitative analysis was used for the calculation of the tumour dose (TD), healthy injected liver dose (HILD), and total injected liver dose. Response was evaluated at 3 months using EASL criteria. Time to progression (TTP) and overall survival (OS) were evaluated using the Kaplan-Meier method. Factors potentially associated with liver toxicity were combined to construct a liver toxicity score (LTS).

RESULTS

The response rate was 78.8%. Median TD were 342 Gy for responding lesions and 191 Gy for nonresponding lesions (p < 0.001). With a threshold TD of 205 Gy, MAA SPECT/CT predicted response with a sensitivity of 100% and overall accuracy of 90%. Based on TD and HILD, 17 patients underwent treatment intensification resulting in a good response rate (76.4%), without increased grade III liver toxicity. The median TTP and OS were 5.5 months (2-9.5 months) and 11.5 months (2-31 months), respectively, in patients with TD <205 Gy and 13 months (10-16 months) and 23.2 months (17.5-28.5 months), respectively, in those with TD >205 Gy (p = 0.0015 and not significant). Among patients with portal vein thrombosis (PVT) (n = 33), the median TTP and OS were 4.5 months (2-7 months) and 5 months (2-8 months), respectively, in patients with TD <205 Gy and 10 months (6-15.2 months) and 21.5 months (12-28.5 months), respectively, in those with TD >205 Gy (p = 0.039 and 0.005). The median OS was 24.5 months (18-28.5 months) in PVT patients with TD >205 Gy and good PVT targeting on MAA SPECT/CT. The LTS was able to detect severe liver toxicity (n = 6) with a sensitivity of 83% and overall accuracy of 97%.

CONCLUSION

Dosimetry based on MAA SPECT/CT was able to accurately predict response and survival in patients treated with glass microspheres. This method can be used to adapt the injected activity without increasing liver toxicity, thus defining a new concept of boosted selective internal radiation therapy (B-SIRT). This new concept and LTS enable fully personalized treatment planning with glass microspheres to be achieved.

Dosimetric considerations in radioimmunotherapy and systemic radionuclide therapies: a review

Radiopharmaceutical therapy, once touted as the “magic bullet” in radiation oncology, is increasingly being used in the treatment of a variety of malignancies; albeit in later disease stages. With ever-increasing public and medical awareness of radiation effects, radiation dosimetry is becoming more important. Dosimetry allows administration of the maximum tolerated radiation dose to the tumor/organ to be treated but limiting radiation to critical organs. Traditional tumor dosimetry involved acquiring pretherapy planar scans and plasma estimates with a diagnostic dose of intended radiopharmaceuticals. New advancements in single photon emission computed tomography and positron emission tomography systems allow semi-quantitative measurements of radiation dosimetry thus allowing treatments tailored to each individual patient.

Quantitative evaluation of scintillation camera imaging characteristics of isotopes used in liver radioembolization

Background

Scintillation camera imaging is used for treatment planning and post-treatment dosimetry in liver radioembolization (RE). In yttrium-90 (90Y) RE, scintigraphic images of technetium-99m (99mTc) are used for treatment planning, while 90Y Bremsstrahlung images are used for post-treatment dosimetry. In holmium-166 (166Ho) RE, scintigraphic images of 166Ho can be used for both treatment planning and post-treatment dosimetry. The aim of this study is to quantitatively evaluate and compare the imaging characteristics of these three isotopes, in order that imaging protocols can be optimized and RE studies with varying isotopes can be compared.

Methodology/Principal Findings

Phantom experiments were performed in line with NEMA guidelines to assess the spatial resolution, sensitivity, count rate linearity, and contrast recovery of 99mTc, 90Y and 166Ho. In addition, Monte Carlo simulations were performed to obtain detailed information about the history of detected photons. The results showed that the use of a broad energy window and the high-energy collimator gave optimal combination of sensitivity, spatial resolution, and primary photon fraction for 90Y Bremsstrahlung imaging, although differences with the medium-energy collimator were small. For 166Ho, the high-energy collimator also slightly outperformed the medium-energy collimator. In comparison with 99mTc, the image quality of both 90Y and 166Ho is degraded by a lower spatial resolution, a lower sensitivity, and larger scatter and collimator penetration fractions.

Conclusions/Significance

The quantitative evaluation of the scintillation camera characteristics presented in this study helps to optimize acquisition parameters and supports future analysis of clinical comparisons between RE studies.

18F-FDG PET independently predicts survival in patients with cholangiocellular carcinoma treated with 90Y microspheres

PURPOSE

(90)Y radioembolization has emerged as a valuable therapy for intrahepatic cholangiocellular carcinomas (ICC). We aimed to evaluate the prognostic power of FDG PET/CT and that of pretherapeutic scintigraphy with (99m)Tc-labelled macroagglutinated albumin (MAA), an index of tumour vascularization.

METHODS

The study group comprised 26 consecutive patients suffering from nonresectable ICC. Before treatment with radioembolization, all patients underwent MRI of the liver, as well as MAA scintigraphy, which was followed immediately by SPECT(/CT) to quantify the liver-lung shunt fraction. Using image fusion, regions of interest were drawn around the tumours and the entire liver, and the tumour-to-liver quotient was calculated. In addition, FDG PET/CT was performed at baseline and 3 months after radioembolization, and the percentage changes in peak (ΔSUV(max)) and mean (ΔSUV(mean)) FDG uptake and in metabolic tumour volume (ΔVol(2SD)) relative to baseline were calculated. Treatment response at 3 months was also assessed using contrast-enhanced MRI and CT on the basis of standard criteria.

RESULTS

Of 23 patients in whom follow-up MRI was available, 5 (22%) showed a partial response, 15 (65%) stable disease and 3 (13%) progressive disease. The change in all FDG values significantly predicted survival by Kaplan-Meier analysis after radioembolization; ΔVol(2SD) responders had a median survival of 97 weeks versus 30 weeks in nonresponders (P = 0.02), whereas ΔSUV(max) and ΔSUV(mean) responders had a median survival of 114 weeks (responder) versus 19 weeks (nonresponder) and 69 weeks in patients with stable disease (P < 0.05). Pretherapeutic MAA scintigraphy or MRI did not predict survival, nor did the presence of extrahepatic metastases, or prior therapies. Only ΔVol(2SD) was significantly associated with survival by univariate analysis (hazard ratio 0.25; P = 0.04) and multivariate analysis (hazard ratio 0.20, P = 0.04).

CONCLUSION

FDG PET/CT was able to predict patient outcome after radioembolization treatment, with the change in metabolically active tumour volume at 3 months being the best independent predictor. High tumour vascularization, as indicated by MAA scintigraphy, was not a prerequisite for successful radioembolization and was even associated with a tendency towards shorter survival.