Large, multifocal or portal vein-invading hepatocellular carcinoma (HCC) downstaged by Y90 using personalized dosimetry: safety, pathological results and outcomes after surgery.

Background: Transarterial radioembolization (TARE) has recently been recognized as a bridging/downstaging therapy to surgery for early hepatocellular carcinomas (HCCs) with high rates of complete pathological necrosis (CPN) on liver explants. In patients with portal vein tumoral thrombus (PVTT), multifocal or large tumors, TARE has mainly a palliative role and surgery remains controversial in this poor-prognosis population. Personalized dosimetry recently proved to outperform standard dosimetry used in prior negative Y90 randomized-controlled trials. Methods: In this retrospective study, we evaluated safety, radiological and pathological response and outcomes in HCC patients with PVTT, multifocal or large tumors, who underwent surgery after downstaging using TARE with Y90-loaded glass microspheres with personalized dosimetry. Results: Between December 2015 and October 2021, 18 unresectable patients (14/18 with PVTT) had surgery (16 resections, 2 liver transplantations) 6.2 months (range, 2-14.6 months) after a single Y90 treatment. No 90-day mortality was reported. Objective modified response criteria in solid tumors (mRECIST) response were noted in all but one patient. Complete and extensive (50-99%) necrosis was observed in 36% and 45% of tumors, respectively. The post-treatment tumor-absorbed dose significantly differed depending on the extent of pathological necrosis (P=0.045). Median overall survival and progression-free survival (PFS) were respectively of 61.8 months [95% CI: 31.4 months-not reached (NR)] and 49.3 months (95% CI: 14 months-NR). PFS was longer in patients with complete imaging response [median NR (none recurred or died) vs. 21.5 months (95% CI: 10.1 months-NR), P<0.001] and in those with complete pathological response [median NR vs. 22.5 months (95% CI: 10.1 months-NR), P<0.001]. Conclusions: Y90 TARE using personalized dosimetry can provide high rates of imaging and pathological response in patients with PVTT, large or multifocal HCC. Subsequent surgery is safe and leads to outcomes far exceeding expectations in an otherwise poor prognosis population with no chance for cure. Trial Registration: Clinical trial number: NCT05045573.

Non-transplantable recurrence after percutaneous thermal ablation of ≤3-cm HCC: Predictors and implications for treatment allocation.

Percutaneous thermal ablation (PTA), resection, and liver transplantation are the standard curative options for hepatocellular carcinoma (HCC). Liver transplantation yields the best long-term outcomes but is limited by graft shortage. Thus, patients with ≤3-cm HCC are primarily treated by PTA even though recurrence is frequent and may occur outside transplant criteria. Data on non-transplantable recurrence (NTR) following PTA are lacking, however. We therefore investigated the incidence and predictors of NTR among 213 potentially transplantable patients (cirrhosis, 93%; Child-Pugh A, 98.6%; alcohol-related disease, 62%) with ≤3-cm HCC(s) treated by PTA, to stratify them according to their NTR risk and to improve treatment allocation. During follow-up (median: 41.2 months), NTR occurred in 18.3% (alpha-fetoprotein [AFP] model) and 23% (Milan) patients. NTR prediction with competing-risk analysis and internal validation revealed AFP > 100 ng/ml (subdistribution hazard ratio: 7.28; p < 0.001) and prior HCC (subdistribution hazard ratio: 3.77; p = 0.002) as independent predictors (Harrell's C: 0.76). Based on this model using the AFP score (equally predictive within Milan criteria), patients were stratified into three NTR risk categories: HCC-naïve with AFP < 100 ng/ml (low risk, n = 108 of 213), non-HCC naïve with AFP < 100 ng/ml (intermediate risk, n = 92 of 213), AFP ≥ 100 ng/ml (high risk, n = 13 of 213), among whom 9.3% (3.7% [Milan]), 22.8% (25% [Milan]), and 61.5% (38/5% [Milan]) presented NTR (p < 0.001). Median recurrence-free survival was 4.6, 14.5, and 43.4 months, respectively, in high-risk, intermediate-risk, and low-risk categories (p < 0.001). Median overall survival, which was 19.1 months in high-risk patients, was not reached otherwise (p < 0.001). Conclusion: Overall, PTA of ≤3-cm HCC incurs a low NTR risk. Simple and noninvasive predictors (HCC naivety, AFP) accurately stratified patients' risk of NTR, and should help to improve treatment allocation. Patients with AFP ≥ 100 ng/ml have a high risk of NTR, poor recurrence-free survival, and overall survival. Further studies evaluating preemptive transplantation or adjuvant/neoadjuvant strategies are highly needed in this small patient subset.

Software-based assessment of tumor margins after percutaneous thermal ablation of liver tumors: A systematic review.

PURPOSE: The purpose of this study was to make a systematic review of clinical studies evaluating software-based tumor margin assessment after percutaneous thermoablation (PTA) of liver tumors. MATERIALS AND METHODS: A systematic literature search was performed through Pubmed/MEDLINE, Embase and the Cochrane Library. Original studies published in English that reported on software-based assessment of ablation margins (AM) following PTA of liver tumors were selected. Studies were analyzed with respect to design, number of patients and tumors, tumor type, PTA technique, tumor size, target registration error, study outcome(s) (subtypes: feasibility, comparative, clinical impact, predictive or survival), and follow-up period. RESULTS: Twenty-nine articles (one multi-center and two prospective studies) were included. The majority were feasibility (26/29, 89.7%) or predictive (23/29, 79.3%) studies. AM was a risk factor of local tumor progression (LTP) in 25 studies (25/29, 86.2%). In nine studies (9/29, 31%) visual assessment overestimated AM compared with software-aided assessment. LTP occurred at the location of the thinnest margin in nine studies (9/29, 31%). Time for registration and analysis was heterogeneously reported, ranging between 5-30 min. Mean target registration error was reported in seven studies (7/29, 24.1%) at 1.62 mm (range: 1.20-2.23 mm). Inter-operator reproducibility was high (kappa range: 0.686-1). Ascites, liver deformation and inconspicuous tumor were major factors of co-registration error. CONCLUSION: Available studies present a low level of evidence overall, since most of them are feasibility, retrospective and single-center studies.

TARE in Hepatocellular Carcinoma: From the Right to the Left of BCLC.

The Barcelona Clinic Liver Cancer (BCLC) system is the most commonly used staging system for hepatocellular carcinoma (HCC) in Western countries. BCLC aims to categorize patients into five stages with different prognoses and to allocate treatment according to these stages based on the best possible contemporary evidence. Transarterial radioembolization (TARE) has recently entered at the left of the BCLC algorithm (i.e., BCLC 0-A), mainly because of negative phase III trials in BCLC C stage. TARE has shown a steady increase in nationwide studies over the past 20 years and has even been adopted in some tertiary centers as the primary HCC treatment across all BCLC stages. We aimed to review the history of TARE in HCC, starting from advanced HCC and gradually expanding to earlier stages at the left of the BCLC system.

Hepatobiliary Scintigraphy and Glass 90Y Radioembolization with Personalized Dosimetry: Dynamic Changes in Treated and Nontreated Liver.

BACKGROUND: The functional changes that occur over time in the liver following 90Y-radioembolization (RE) using personalized dosimetry (PD) remain to be investigated. METHODS: November 2016-October 2019: we retrospectively included hepatocellular carcinoma (HCC) patients treated by 90Y-glass RE using PD, who underwent hepatobiliary scintigraphy (HBS) at baseline and at 15 days, 1, 2, 3, and 6 months after RE. RESULTS: There were 16 patients with unilobar disease (100%) included, and 64 HBS were performed. Whole liver function significantly decreased over time. The loss was maximal at 2 weeks: -32% (p = 0.002) and remained below baseline at 1 (-15%; p = 0.002), 2 (-25%; p < 0.001), and 3 months (-16%; p = 0.027). No radioembolization-induced liver disease was observed. Treated liver function strongly decreased to reach -64% (p < 0.001) at 2 months. Nontreated liver function decreased at 2 weeks (-21%; p = 0.027) and remained below baseline before reaching +20% (p = 0.002) and +59% (p < 0.001) at 3 and 6 months, respectively. Volumetric and functional changes exhibited parallel evolutions in the treated livers (p = 0.01) but independent evolutions in the nontreated livers (p = 0.08). CONCLUSION: RE using PD induces significant regional changes in liver function over time. As early as 15 days following RE, both the treated and nontreated livers showed a decreased function. Nontreated liver function recovered after 3 months and greatly increased afterwards.

Uni-, Bi- or Trifocal Hepatocellular Carcinoma in Western Patients: Recurrence and Survival after Percutaneous Thermal Ablation.

Multifocality is usually reported as a pejorative factor after percutaneous thermal ablation (PTA) of HCC but little is known in Western series. Recurrence and survival were extracted from a prospective database of all patients who underwent PTA for ≤3 cm HCC. From January 2015 to April 2020, we analyzed 281 patients with unifocal (n = 216), bifocal (n = 46) and trifocal (n = 16) HCC. PTA of bi- and trifocal HCC resulted in a high risk of very early (<6 months) distant recurrence (38.8% and 50%, respectively). Median RFS was 23.3 months (95% CI:18.6-30.4), 7.7 months (95% CI:5.1-11.43, p = 0.002) and 5.2 months (95% CI:3-12.3, p = 0.015), respectively, for uni-, bi- and trifocal HCC groups. In a multivariate analysis, both bifocal (HR = 2.46, p < 0.001) and trifocal (HR = 2.70, p = 0.021) vs. unifocal HCC independently predicted shorter RFS. Median OS in trifocal HCC group was 30.3 months (95 CI:19.3-not reached). Trifocal vs. unifocal HCC independently predicted shorter OS (HR = 3.30, p = 0.008), whereas bifocal vs. unifocal HCC did not (p = 0.27). Naïve patient (HR = 0.42, p = 0.007), AFP > 100 ng/mL (HR = 3.03, p = 0.008), MELD > 9 (HR = 2.84, p = 0.001) and steatotic HCC (HR = 0.12, p = 0.038) were also independent predictors of OS. In conclusion, multifocal HCCs in a Western population have a dramatically increased risk of distant recurrence. OS after PTA of trifocal HCC is significantly below what was expected after a curative treatment.

Deportalization, Venous Congestion, Venous Deprivation: Serial Measurements of Volumes and Functions on Morphofunctional 99mTc-Mebrofenin SPECT-CT.

The objective was to assess the changes in regional volumes and functions under venous-impaired vascular conditions following liver preparation. Twelve patients underwent right portal vein embolization (PVE) (n = 5) or extended liver venous deprivation (eLVD, i.e., portal and right and middle hepatic veins embolization) (n = 7). Volume and function measurements of deportalized liver, venous-deprived liver and congestive liver were performed before and after PVE/eLVD at days 7, 14 and 21 using 99mTc-mebrofenin hepatobiliary scintigraphy with single-photon emission computed tomography and computed tomography (99mTc-mebrofenin SPECT-CT). Volume and function progressed independently in the deportalized liver (p = 0.47) with an early decrease in function (median -18.2% (IQR, -19.4--14.5) at day 7) followed by a decrease in volume (-19.3% (-22.6--14.4) at day 21). Volume and function progressed independently in the venous deprived liver (p = 0.80) with a marked and early decrease in function (-41.1% (-52.0--12.9) at day 7) but minimal changes in volume (-4.7% (-10.4-+3.9) at day 21). Volume and function progressed independently in the congestive liver (p = 0.21) with a gradual increase in volume (+43.2% (+38.3-+51.2) at day 21) that preceded a late and moderate increase in function at day 21 (+34.8% (-8.3-+46.6)), concomitantly to the disappearance of hypoattenuated congestive areas in segment IV (S4) on CT, initially observed in 6/7 patients after eLVD and represented 35.3% (22.2-46.4) of whole S4 volume. Liver volume and function progress independently whatever the vascular condition. Hepatic congestion from outflow obstruction drives volume increase but results in early impaired function.

Multimodal Percutaneous Thermal Ablation of Small Hepatocellular Carcinoma: Predictive Factors of Recurrence and Survival in Western Patients.

BACKGROUND: To identify the predictive factors of recurrence and survival in an unselected population of Western patients who underwent multimodal percutaneous thermal ablation (PTA) for small Hepatocellular Carcinomas (HCCs). METHODS: January 2015-June 2019: data on multimodal PTA for <3 cm HCC were extracted from a prospective database. Local tumor progression (LTP), intrahepatic distant recurrence (IDR), time-to-LTP, time-to-IDR, recurrence-free (RFS) and overall (OS) survival were evaluated. RESULTS: 238 patients underwent 317 PTA sessions to treat 412 HCCs. During follow-up (median: 27.1 months), 47.1% patients had IDR and 18.5% died. LTP occurred after 13.3% of PTA. Tumor size (OR = 1.108, p < 0.001; hazard ratio (HR) = 1.075, p = 0.002) and ultrasound guidance (OR = 0.294, p = 0.017; HR = 0.429, p = 0.009) independently predicted LTP and time-to-LTP, respectively. Alpha fetoprotein (AFP) > 100 ng/mL (OR = 3.027, p = 0.037) and tumor size (OR = 1.06, p = 0.001) independently predicted IDR. Multinodular HCC (HR = 2.67, p < 0.001), treatment-naïve patient (HR = 0.507, p = 0.002) and AFP > 100 ng/mL (HR = 2.767, p = 0.014) independently predicted time-to-IDR. RFS was independently predicted by multinodular HCC (HR = 2.144, p = 0.001), treatment naivety (HR = 0.546, p = 0.004) and AFP > 100 ng/mL (HR = 2.437, p = 0.013). The American Society of Anesthesiologists (ASA) score > 2 (HR = 4.273, p = 0.011), AFP (HR = 1.002, p < 0.001), multinodular HCC (HR = 3.939, p = 0.003) and steatotic HCC (HR = 1.81 × 10-16, p < 0.001) independently predicted OS. CONCLUSIONS: IDR was associated with tumor aggressiveness, suggesting a metastatic mechanism. Besides AFP association with LTP, IDR, RFS and OS, treatment-naïve patients had longer RFS, and multi-nodularity was associated with shorter RFS and OS. Steatotic HCC, identified on pre-treatment MRI, independently predicted longer OS, and needs to be further explored.

Learning curve of liver stiffness measurement using a new hybrid machine composed of transient elastography interfaced with ultrasound.

OBJECTIVES: To assess the learning curve for performing reliable liver stiffness measurements using a new hybrid machine composed of transient elastography (TE) interfaced with an ultrasound device for radiographers and radiologists with different levels of expertise in ultrasound imaging. METHODS: Ten novice operators who had never performed TE measurements were prospectively evaluated from April to October 2018: senior radiologists, young radiologists, fellows, radiographers, and residents, with different levels of experience in abdominal ultrasound imaging. All operators had a short theoretical training followed by a training session under supervision in three patients. Then, each operator had to perform TE in 50 consecutive patients with chronic liver disease, using beforehand ultrasound examination to select measurement area in the right liver lobe, and if needed, the XL probe. Percentages of failures and reliable measurements were compared. RESULTS: The rates of failures of measurements, poorly reliable, reliable, and very reliable results, were of 4.2% (21/500), 2.4% (12/500), 47.6% (238/500), and 45.8% (229/500), respectively. The rates of reliable plus very reliable results were excellent, ranging from 91 to 96% among all the subgroups. The rates of very reliable, reliable, and unreliable results did not differ between operator subgroups and especially between junior radiologists, senior radiologists, and radiographers. No breaking point was observed in the interquartile range/median values over time. CONCLUSION: TE interfaced with ultrasound in this hybrid machine presents no learning curve effect. After a short initial training session, a novice observer is able to perform high rates of reliable and very reliable TE measurements. KEY POINTS: • When performing liver stiffness measurements using a new hybrid machine composed of transient elastography interfaced with ultrasound, the rate of failures of measurements is very low, below 5%. • After a short training session and using ultrasound planning, a novice operator, whatever its expertise in ultrasound imaging, is capable of performing high rates of reliable and very reliable measurements. • No learning curve is needed for performing reliable liver stiffness measurements using this new hybrid machine.

Analysis of differences between 99mTc-MAA SPECT- and 90Y-microsphere PET-based dosimetry for hepatocellular carcinoma selective internal radiation therapy.

BACKGROUND: The aim of this study was to compare predictive and post-treatment dosimetry and analyze the differences, investigating factors related to activity preparation and delivery, imaging modality used, and interventional radiology. METHODS: Twenty-three HCC patients treated by selective internal radiation therapy with 90Y glass microspheres were included in this study. Predictive and post-treatment dosimetry were calculated at the voxel level based on 99mTc-MAA SPECT/CT and 90Y-microsphere PET/CT respectively. Dose distribution was analyzed through mean dose, metrics extracted from dose-volume histograms, and Dice similarity coefficients applied on isodoses. Reproducibility of the radiological gesture and its influence on dose deviation was evaluated. RESULTS: 90Y delivered activity was lower than expected in 67% (16/24) of the cases mainly due to the residual activity. A mean deviation of - 6 ± 11% was observed between the delivered activity and the 90Y PET's FOV activity. In addition, a substantial difference of - 20 ± 8% was measured on 90Y PET images between the activity in the liver and in the whole FOV. After normalization, 99mTc-MAA SPECT dosimetry was highly correlated and concordant with 90Y-microsphere PET dosimetry for all dose metrics evaluated (ρ = 0.87, ρc = 0.86, P = 3.10-8 and ρ = 0.91, ρc = 0.90, P = 7.10-10 for tumor and normal liver mean dose respectively for example). Besides, mean tumor dose deviation was lower when the catheter position was identical than when it differed (16 Gy vs. 37 Gy, P = 0.007). Concordance between predictive and post-treatment dosimetry, evaluated with Dice similarity coefficients applied on isodoses, significantly correlated with the distance of the catheter position from artery bifurcation (P = 0.04, 0.0004, and 0.05, for 50 Gy, 100 Gy, and 150 Gy isodoses respectively). CONCLUSIONS: Discrepancies between planned activity and activity measured on 90Y PET images were observed and seemed to be mainly related to clinical hazards and equipment issues. Predictive vs. post-treatment comparison of relative dose distributions between tumor and normal liver showed a good correlation and no significant difference highlighting the predictive value of 99mTc MAA SPECT/CT-based dosimetry. Besides, the reproducibility of catheter tip position appears critical in the agreement between predictive and actual dose distribution.

Transarterial Chemoembolization of Hepatocellular Carcinoma with Idarubicin-Loaded Tandem Drug-Eluting Embolics.

: Objective: To describe the responses, toxicities and outcomes of HCC patients treated by transarterial chemoembolization (TACE) using idarubicin-loaded TANDEM beads. Materials and Methods: Seventy-two consecutive patients (mean age: 71 years (58-84 years)) with HCC were treated by TACE using idarubicin-loaded TANDEM in a first line, over a five-year period. Most patients (89%) had liver cirrhosis classified as Child-Pugh A (90%). BCLC B classification applied in 85% of cases. Baseline tumor burden was limited to one to three nodules in 92% of cases, unilobar in 88% cases, with a median tumor diameter of 55 mm (range: 13-150 mm). Toxicity was assessed using NCI CTC AE v4.0. Response was assessed using mRECIST criteria. Time-to-treatment failure (TTTF) and overall survival (OS) were also calculated based on Kaplan-Meier method. Result: Of 141 TACE sessions performed with bead sizes of 100 and 75 µm in 42 (29.8%) and 99 (70.2%) sessions, respectively. In 78% of all TACE sessions, the full dose of idarubicin-loaded beads was injected. Grade 3-4 AE were observed after 73 (52%) sessions, most of them being biological. Multi-organ failure was observed three days after the first TACE in a Child B patients, unfortunately leading to death. Overall, the best objective response rate (ORR) was 65%. Median follow-up lasted 14.3 months (95% CI: 11.2-18.8 months). Median TTTF and OS were 14.4 months (95% CI: 7.2-24.6 months) and 34.6 months (95% CI: 24.7-not reached) respectively. Conclusion: In this retrospective study involving well-selected HCC patients, high ORR and long TTTF and OS are observed after TACE using idarubicin-loaded TANDEM. A randomized trial is needed.

Radiation Exposure During Transarterial Chemoembolization: Angio-CT Versus Cone-Beam CT.

INTRODUCTION: Cone-beam computed tomography (CBCT) has been developed to improve reliability of many interventional radiology (IR) procedures performed with Angio system, such as transarterial chemoembolization (TACE). Angio-CT has emerged as a new imaging technology that combines a CT scanner with an Angio system in the same IR suite. The purpose of our study was to compare Angio system with CBCT capability and Angio-CT in terms of patient radiation exposure during TACE procedures. MATERIALS AND METHODS: Consecutive TACE procedures performed between January 2016 and September 2017 with the two imaging modalities (Artis Zeego defining the CBCT group and Infinix-i 4D-CT defining the Angio-CT group) were reviewed. TACE and patient's characteristics and patient radiation exposure parameters were collected. Dose-area products (DAP) and dose-length products (DLP) were converted into effective doses (ED) using conversion factors. Accuracy of tumor targeting and response was retrospectively assessed. RESULTS: A total of 114 TACE procedures in 96 patients were included with 57 procedures in each group. The total ED in the Angio-CT group was 2.5 times lower than that in the CBCT group (median 15.4 vs. 39.2 mSv, p < 0.001). Both 2D ED and 3D ED were lower in the Angio-CT group than in the CBCT group (5.1 vs. 20 mSv, p < 0.001, and 7.4 vs. 17.9 mSv, p < 0.001, respectively). There was no significant difference neither in terms of classes of tumor targeting (p = 0.509) nor in terms of classes of tumor response (p = 0.070) between both groups. CONCLUSION: Angio-CT provides significant decrease in patient effective dose during TACE procedures compared to Angio system with CBCT.

Tumor Targeting and Three-Dimensional Voxel-Based Dosimetry to Predict Tumor Response, Toxicity, and Survival after Yttrium-90 Resin Microsphere Radioembolization in Hepatocellular Carcinoma.

PURPOSE: To identify predictive factors of tumor response, progression-free survival (PFS), overall survival (OS), and toxicity using three-dimensional (3D) voxel-based dosimetry in patients with intermediate and advanced stage hepatocellular carcinoma (HCC) treated by yttrium-90 (90Y) resin microspheres radioembolization (RE). MATERIALS AND METHODS: From February 2012 to December 2015, 45 90Y resin microspheres RE procedures were performed for HCC (Barcelona Clinic Liver Cancer stage B/C; n = 15/30). Area under the dose-volume histograms (AUDVHs) were calculated from 3D voxel-based dosimetry to measure 90Y dose deposition. Factors associated with tumor control (ie, complete/partial response or stable disease on Modified Response Evaluation Criteria in Solid Tumors) at 6 months were investigated. PFS and OS analyses were performed (Kaplan-Meier). Toxicity was assessed by occurrence of radioembolization-induced liver disease (REILD). RESULTS: Tumor control rate was 40.5% (17/42). Complete tumor targeting (odds ratio = 36.97; 95% confidence interval, 1.83-747; P < .001) and AUDVHtumor (odds ratio = 1.027; 95% confidence interval, 1.002-1.071; P = .033) independently predicted tumor control. AUDVHtumor ≥ 61 Gy predicted tumor control with 76.5% sensitivity and 75% specificity. PFS and OS in patients with incomplete tumor targeting were significantly shorter than in patients with complete tumor targeting (median PFS, 2.7 months [range, 0.8-4.6 months] vs 7.9 months [range, 2.1-39.5 months], P < .001; median OS, 4.5 months [range, 1.4-23 months] vs 19.2 months [range, 2.1-46.9 months], P < .001). Patients with incomplete tumor targeting and AUDVHtumor < 61 Gy, incomplete tumor targeting and AUDVHtumor > 61 Gy, complete tumor targeting and AUDVHtumor < 61 Gy, and AUDVHtumor > 61 Gy had median PFS of 2.7, 1.8, 6.3, and 12.1 months (P < .001). REILD (n = 4; 9.5%) was associated with higher dose delivered to normal liver (P = .04). CONCLUSIONS: Complete tumor targeting and 90Y dose to tumor are independent factors associated with tumor control and clinical outcomes.

Retrospective Voxel-Based Dosimetry for Assessing the Ability of the Body-Surface-Area Model to Predict Delivered Dose and Radioembolization Outcome.

The aim of this study was to quantitatively evaluate the ability of the body-surface-area (BSA) model to predict tumor-absorbed dose and treatment outcome through retrospective voxel-based dosimetry. Methods: Data from 35 hepatocellular carcinoma patients with a total of 42 90Y-resin microsphere radioembolization treatments were included. Injected activity was planned with the BSA model. Voxel dosimetry based on 99mTc-labeled macroaggregated albumin SPECT and 90Y-microsphere PET was retrospectively performed using a dedicated treatment planning system. Average dose and dose-volume histograms (DVHs) of the anatomically defined tumors were analyzed. The selected dose metrics extracted from DVHs were minimum dose to 50% and 70% of the tumor volume and percentage of the volume receiving at least 120 Gy. Treatment response was evaluated 6 mo after therapy according to the criteria of the European Association for the Study of the Liver. Results: Six-month response was evaluated in 26 treatments: 14 were considered to produce an objective response and 12 a nonresponse. Retrospective evaluation of 90Y-microsphere PET-based dosimetry showed a large interpatient variability with a median average absorbed dose of 60 Gy to the tumor. In 62% (26/42) of the cases, tumor, nontumoral liver, and lung doses would have complied with the recommended thresholds if the injected activity calculated by the BSA method had been increased. Average doses, minimum dose to 50% and 70% of the tumor volume, and percentage of the volume receiving at least 120 Gy were significantly higher in cases of objective response than in nonresponse. Conclusion: In our population, average tumor-absorbed dose and DVH metrics were associated with tumor response. However, the activity calculated by the BSA method could have been increased to reach the recommended tumor dose threshold. Tumor uptake, target and nontarget volumes, and dose distribution heterogeneity should be considered for activity planning.