RADIOACTIVE ISOTOPES FOR ADJUVANT CANCER THERAPY; ANIMAL EXPERIMENTATION AND PRELIMINARY RESULTS IN HUMAN APPLICATION

Standard Radiation Dosimetry Models: What Interventional Radiologists Need to Know

Thoughtful and accurate dosimetry is critical to obtain the safest and most efficacious yttrium-90 (Y90) radioembolization of primary and secondary liver cancers. Three dosimetry models are currently used in clinical practice, namely, body surface area model, medical internal radiation dose model, and the partition model. The objective of this review is to briefly outline the history behind Y90 dosimetry and the difference between the aforementioned models. When applying these three models to a single case, the differences between them are further demonstrated. Each dosimetry model in clinical practice has its own benefits and limitations. Therefore, it is incumbent upon practicing interventional radiologists to be aware of these differences to optimize treatment outcomes for their patients.

Yttrium-90 hepatic radioembolization: clinical review and current techniques in interventional radiology and personalized dosimetry

In recent years, yttrium-90 ((90)Y) microsphere radioembolization has been establishing itself as a safe and efficacious treatment for both primary and metastatic liver cancers. This extends to both first-line therapies as well as in the salvage setting. In addition, radioembolization appears efficacious for patients with portal vein thrombosis, which is currently a contraindication for surgery, transplantation and transarterial chemoembolization. This article reviews the efficacy and expanding use of (90)Y microsphere radioembolization with an added emphasis on recent advances in personalized dosimetry and interventional radiology techniques. Directions for future research into combination therapies with radioembolization and expansion into sites other than the liver are also explored.

Evaluation of factors affecting tumor response and survival in patients with primary and metastatic liver cancer treated with microspheres

OBJECTIVE

Radioembolization with the yttrium-90 (Y-90) microspheres is being used increasingly more often in the treatment of patients with primary or metastatic liver cancer. Although technetium-99m macroaggregated albumin (Tc-99m MAA) scintigraphy performed following diagnostic angiography has an important role in predicting the effectiveness of treatment and in dose estimation, the number of studies using quantitative assessment of Tc-99m MAA scintigraphy is limited in this field. In the present study, the aim was to assess whether a tumor dose is required to obtain objective tumor response and to check whether this threshold value is predictive in terms of tumor response, survival, and liver toxicity by using Tc-99m MAA single-photon emission computed tomography (SPECT) images.

MATERIALS AND METHODS

Overall, 54 patients (20 women and 34 men; median age: 60 years) who underwent Y-90 Resin (SIR-Spheres) and Glass (TheraSphere) microsphere treatment with a diagnosis of unresectable liver cancer between August 2010 and April 2013 were included in the study. The mean doses to normal liver and tumor were estimated for each patient using Tc-99m MAA SPECT images and the medical internal radiation dosimetry method. The responses were assessed according to Response Evaluation Criteria In Solid Tumors (RECIST) and European Organisation for Research and Treatment of Cancer (EORTC) criteria. Kaplan-Meier survival curves and univariate Cox regression analysis were used in survival analysis. The relationship between treatment response and other parameters included was assessed using logistic regression analysis. The variables with a P value less than 0.01 in univariate analysis were assessed with multivariate analysis.

RESULTS

Fifty-four Y-90 microsphere treatments (eight by using a Y-90 glass microsphere and 46 by using a Y-90 resin microsphere) were performed. In the multivariate analysis, the only parameter related to response was tumor dose (P<0.01). With a tumor dose of 280 Gy or higher, objective tumor response was observed in 59 and 77% of the patients according to RECIST and EORTC criteria, respectively, and the tumor control rate was found to be 95% according to both criteria. In addition, it was found that only tumor dose was correlated with progression-free survival (PFS) (P<0.001) and overall survival (OS) (P=0.018). When the tumor dose was 280 Gy or higher, median PFS increased from 2 to 10.7 months (P<0.001), whereas median OS increased from 9 to 17.6 months (P=0.018). However, reversible ≥ G2 liver toxicity was observed in 3.7% (2/54) of the patients within 3 months after radioembolization with a median normal liver dose of 40 Gy (10-102 Gy). There was reversible ≥ G3 liver toxicity in 3.7% (2/54) of patients, but no G4 liver toxicity was observed. Clinical radiation hepatitis and treatment-induced liver failure were not observed in any of these patients.

CONCLUSION

Tc-99m MAA SPECT has a predictive value in terms of response to radioembolization, PFS, and OS. Dosimetry based on Tc-99m MAA SPECT images can be used in the selection of patients and, in particular, to adaptation of treatment plan in selected patients.

Liver resection for metastatic disease after y90 radioembolization: a case series with long-term follow-up

INTRODUCTION

There are only few reports of liver resections for metastatic disease in patients previously treated with Y-90 radioembolization (RE), and long-term outcome data are sparse. We reviewed our center's experience in patients undergoing hepatectomy after hepatic RE.

METHODS

A retrospective chart review of patients undergoing RE from 2004 to 2011 was performed. Demographic, clinicopathologic, operative, and long-term outcomes variables were collected. Independent pathologic review of tumor necrosis and normal liver tissue grading of fibrosis and inflammation after resection was performed. Data are expressed as medians and ranges.

RESULTS

RE was delivered to 106 patients with primary and metastatic disease of the liver, of whom 9 patients (6 males, 3 females, median age 54 (47-76) years) with metastatic disease ultimately underwent resection. RE was previously administered to the right liver in five, the left liver in one, and to the whole liver in three. Two patients had a second RE performed before resection. Six of the nine patients had previously received several infusions of cytotoxic therapy. The operations occurred at a median of 115 (56-245) days after RE and included right lobectomy (n = 5), left lobectomy (n = 1), left-lateral sectionectomy (n = 1), and bilobar wedge resections (n = 2). Extrahepatic sites were resected in three patients. Median blood loss was 900 (range 250-3600) ml. Grade 3 or higher complications occurred in seven cases (78 %). Follow-up was complete all nine patients. Three patients (33 %) died within 30 days of resection. All those surviving the operative period had disease recurrence (time to recurrence: 202 [range 54-315] days), and all have since died (overall survival: 584 [range 127-1230] days). Review of resected specimens demonstrated median tumor necrosis of 70 % (range 20-90 %). In nontumor-bearing liver, fibrosis grade (0-4) and inflammation score (0-4) was 2 or less in all specimens.

CONCLUSIONS

In this small cohort of highly selected and heavily pretreated patients, long-term survival in patients undergoing resection after RE appears possible, but the operations may carry substantial risks-highlighting the importance of careful patient selection for these resections. The etiology of morbidity and mortality is likely multifactorial and additional reports that include long-term outcomes will be necessary to identify more clearly the impact of RE on postoperative complications and death.

Immunogenic cell death biomarkers HMGB1, RAGE, and DNAse indicate response to radioembolization therapy and prognosis in colorectal cancer patients

Radioembolization therapy (RE) is an efficient locoregional treatment for liver metastases from colorectal cancer. Serum biomarkers involved in immunogenic cell death are potentially valuable for early predicting therapy response and estimating prognosis. In a prospective observation study, blood samples were taken from 49 consecutive colorectal cancer patients with extensive hepatic metastases before, 24 and 48 hr after RE. Serum levels of high mobility group box 1 (HMGB1), receptor of glycation end products (RAGE) and activity of desoxyribonuclease were compared with response to therapy regularly determined radiologically 3 months after therapy and with overall survival. Serum levels of HMGB1 were increased already 24 hr after RE, while RAGE levels were decreased and DNAse remained unchanged. In radiological staging, 35 patients demonstrated disease progression while 14 patients had stable disease or remission. Serum HMGB1 levels 24 hr after RE were significantly higher in progressive than in nonprogressive patients while for RAGE and DNAse no difference was observed between the response groups. Concerning overall survival, high pretherapeutic (0 hr) and 24 hr levels of HMGB1 were associated with poor outcome. Multivariate analysis including HMGB1, tumor, liver and inflammation markers revealed HMGB1 and CRP as independent prognostic parameters. HMGB1 is a valuable serum biomarker for early estimation of therapy response and prognosis in colorectal cancer patients with liver metastases undergoing RE therapy.

Predictive and prognostic value of circulating nucleosomes and serum biomarkers in patients with metastasized colorectal cancer undergoing Selective Internal Radiation Therapy

Background

Selective Internal Radiation Therapy (SIRT) is a new and effective locoregional anticancer therapy for colorectal cancer patients with liver metastases. Markers for prediction of therapy response and prognosis are needed for the individual management of those patients undergoing SIRT.

Methods

Blood samples were prospectively and consecutively taken from 49 colorectal cancer patients with extensive hepatic metastases before, three, six, 24 and 48 h after SIRT to analyze the concentrations of nucleosomes and further laboratory parameters, and to compare them with the response to therapy regularly determined 3 months after therapy and with overall survival.

Results

Circulating nucleosomes, cytokeratin-19 fragments (CYFRA 21-1), carcinoembryonic antigen (CEA), C-reactive protein (CRP) and various liver markers increased already 24 h after SIRT. Pretherapeutical levels of CYFRA 21-1, CEA, cancer antigen 19-9 (CA 19-9), asparate-aminotransferase (AST) and lactate dehydrogenase (LDH) as well as 24 h values of nucleosomes were significantly higher in patients suffering from disease progression (N = 35) than in non-progressive patients (N = 14). Concerning overall survival, CEA, CA 19-9, CYFRA 21-1, CRP, LDH, AST, choline esterase (CHE), gamma-glutamyl-transferase, alkaline phosphatase, and amylase (all 0 h, 24 h) and nucleosomes (24 h) were found to be prognostic relevant markers in univariate analyses. In multivariate Cox-Regression analysis, the best prognostic model was obtained for the combination of CRP and AST. When 24 h values were additionally included, nucleosomes (24 h) further improved the existing model.

Conclusion

Panels of biochemical markers are helpful to stratify pretherapeutically colorectal cancer patients for SIR-therapy and to early estimate the response to SIR-therapy.

Yttrium-90 (90Y) in the principal radionuclide therapies: an efficacy correlation between peptide receptor radionuclide therapy, radioimmunotherapy and transarterial radioembolization therapy. Ten years of experience (1999-2009)

The clinical application of the pure beta emitter (90)Y constitutes a fundamental advancement in non-invasive medicine. Nowadays, mainly three oncological therapies exploit the intrinsic emissive characteristic of (90)Y. Radionuclide therapies include peptide receptor radionuclide therapy (PRRT) in neuroendocrine tumour (NET) treatment, radioimmunotherapy (RIT) in non-Hodgkin's lymphoma (NHL) treatment and transarterial radioembolization therapy (TARET) in unresectable hepatocellular carcinoma (HCC) and liver metastatic colorectal cancer (mCRC) treatment. The last ten years of clinical experience from E-PubMed research have been reviewed and an efficacy correlation between (90)Y-therapies has shown a better objective response rate for RIT (ORR 80±15%; range 53-100) compared to PRRT (ORR 23.5±14%; range 9-50), and TARET (ORR for mCRC, 40±25%; range 19-91, and ORR for HCC, 42±20%; range 20-82). This review reports on the state of the art of the efficacy of (90)Y-therapies from the last decade and discusses new perspectives of therapeutic development.

Radioembolization (yttrium-90 microspheres) for primary and metastatic hepatic malignancies

Radioembolization using radioactive yttrium-90-labeled microspheres is gaining a stronger foothold in the management of primary and metastatic hepatic cancers. The expanding literature reveals good and encouraging results in both retrospective and prospective reports as demonstrated by low acute or late toxicity and high response rates. This treatment modality, which is most beneficial in patients with good liver reserve and low Eastern Cooperative Oncology Group performance status, has led to improved time to liver progression and extended overall patient survival. Although the phase III trials of radioembolization are ongoing as a first-line treatment of patients with metastatic colorectal cancer, there are sufficient phase II and retrospective clinical data supporting its use in salvage therapy for most patients. Patients with hepatocellular cancer, neuroendocrine tumors, and other primary sites, including breast and lung, have also shown promising response and survival increases in multi-institutional experiences.

Radioembolisation using yttrium 90 (Y-90) in patients affected by unresectable hepatic metastases

PURPOSE

This study was done to evaluate the effectiveness of radioembolisation of liver metastases with yttrium 90 (Y-90) in patients with no response to chemotherapy.

MATERIALS AND METHODS

From February 2005 to January 2008, we treated 110 patients affected by liver metastatic disease from colorectal, breast, gastric, pancreatic, pulmonary, oesophageal and pharyngeal cancers and from cholangiocarcinoma and melanoma. We excluded patients with bilirubin level >1.8 mg/dl and pulmonary shunt >20% but not patients with minor extrahepatic metastases.

RESULTS

We obtained a complete /partial response in 45 patients, stable disease in 42 patients and progressive disease in 23 patients. In 90 cases, we obtained a decrease in specific tumour marker level. The technical success rate was 96%, and technical effectiveness estimated at 3 months after treatment was 83.6%. Side effects were grade 4 hepatic failure in one case, grade 2 gastritis in six cases and grade 2 cholecystitis in two cases. The median survival and progression-free survival calculated by Kaplan-Meier analysis were 323 days and 245 days, respectively.

CONCLUSIONS

According to our 3-year experience, Y-90 radioembolisation (SIR-spheres) is a feasible and safe method to treat liver metastases with an acceptable level of complications and a good response rate.

Computer modeling of yttrium-90-microsphere transport in the hepatic arterial tree to improve clinical outcomes

PURPOSE

Radioembolization (RE) via yttrium-90 ((90)Y) microspheres is an effective and safe treatment for unresectable liver malignancies. However, no data are available regarding the impact of local blood flow dynamics on (90)Y-microsphere transport and distribution in the human hepatic arterial system.

METHODS AND MATERIALS

A three-dimensional (3-D) computer model was developed to analyze and simulate blood-microsphere flow dynamics in the hepatic arterial system with tumor. Supplemental geometric and flow data sets from patients undergoing RE were also available to validate the accuracy of the computer simulation model. Specifically, vessel diameters, curvatures, and branching patterns, as well as blood flow velocities/pressures and microsphere characteristics (i.e., diameter and specific gravity), were measured. Three-dimensional computer-aided design software was used to create the vessel geometries. Initial trials, with 10,000 noninteracting microspheres released into the hepatic artery, used resin spheres 32-microm in diameter with a density twice that of blood.

RESULTS

Simulations of blood flow subject to different branch-outlet pressures as well as blood-microsphere transport were successfully carried out, allowing testing of two types of microsphere release distributions in the inlet plane of the main hepatic artery. If the inlet distribution of microspheres was uniform (evenly spaced particles), a greater percentage would exit into the vessel branch feeding the tumor. Conversely, a parabolic inlet distribution of microspheres (more particles around the vessel center) showed a high percentage of microspheres exiting the branch vessel leading to the normal liver.

CONCLUSIONS

Computer simulations of both blood flow patterns and microsphere dynamics have the potential to provide valuable insight on how to optimize (90)Y-microsphere implantation into hepatic tumors while sparing normal tissue.

Selective internal radiation therapy with SIR-spheres for the treatment of unresectable colorectal hepatic metastases

The purpose of this study was to evaluate the effectiveness of colorectal cancer (CRC) liver metastasis radioembolization with yttrium-90 (Y90), assessing toxicity and survival rates in patients with no response to chemotherapy through our 3-year experience. From February 2005 to January 2008, we treated 41 patients affected by CRC from a cohort of selective internal radiation therapy patients treated at our institution. All patients examined showed disease progression and arrived for our observation with an abdominal CT, a body PET, and a hepatic angiography followed by gastroduodenal artery coiling previously performed by us. We excluded patients with a bilirubin level>1.8 mg/dl and pulmonary shunt>20% but not patients with minor extrahepatic metastases. On treatment day, under fluoroscopic guidance, we implanted a dose of Y90 microspheres calculated on the basis of liver tumoral involvement and the body surface area formula. All patients were discharged the day after treatment. We obtained, according to Response Evaluation Criteria on Solid Tumors, a complete response in 2 patients, a partial response in 17 patients, stable disease in 14 patients, and progressive disease in 8 patients. In all cases, we obtained a carcinoembryonic antigen level decrease, especially in the week 8 evaluation. Technical success rate was 98% and technical effectiveness estimated at 3 months after treatment was 80.5%. Side effects graded by Common Terminology Criteria on Adverse Events were represented by one grade 4 hepatic failure, two grade 2 gastritis, and one grade 2 cholecystitis. The median survival and the progression-free survival calculated by Kaplan-Meier analysis were 354 and 279 days, respectively. In conclusion, according to our 3-year experience, Y90 SIR-Spheres radioembolization is a feasible and safe method to treat CRC liver metastases, with an acceptable level of complications and a good response rate.

A first report of radioembolization for hepatic metastases from ocular melanoma

BACKGROUND

Ocular melanoma (OM) metastasizes to the liver and is rapidly fatal despite aggressive therapy. Yttrium-90 microspheres (radioembolization) delivered via the hepatic artery is an established and effective approach for primary and metastatic hepatic tumors, although (90)Y use in OM has not been reported previously.

METHODS

A retrospective review was performed for all patients with OM who received radioembolization at 5 centers.

RESULTS

11 patients received 12 treatments with a median activity of 1.55 GBq delivered per treatment. Toxicity was minimal, with PET/CT at 3 months posttreatment showing a response in all patients; 1 patient had a complete response.

CONCLUSIONS

Radioembolization can control hepatic metastases of OM with very few side effects.

Treatment parameters and outcome in 680 treatments of internal radiation with resin 90Y-microspheres for unresectable hepatic tumors

PURPOSE

Radioembolization (RE) using (90)Y-microspheres is an effective and safe treatment for patients with unresectable liver malignancies. Radiation-induced liver disease (RILD) is rare after RE; however, greater understanding of radiation-related factors leading to serious liver toxicity is needed.

METHODS AND MATERIALS

Retrospective review of radiation parameters was performed. All data pertaining to demographics, tumor, radiation, and outcomes were analyzed for significance and dependencies to develop a predictive model for RILD. Toxicity was scored using the National Cancer Institute Common Toxicity Criteria Adverse Events Version 3.0 scale.

RESULTS

A total of 515 patients (287 men; 228 women) from 14 US and 2 EU centers underwent 680 separate RE treatments with resin (90)Y-microspheres in 2003-2006. Multifactorial analyses identified factors related to toxicity, including activity (GBq) Selective Internal Radiation Therapy delivered (p < 0.0001), prescribed (GBq) activity (p < 0.0001), percentage of empiric activity (GBq) delivered (p < 0.0001), number of prior liver treatments (p < 0.0008), and medical center (p < 0.0001). The RILD was diagnosed in 28 of 680 treatments (4%), with 21 of 28 cases (75%) from one center, which used the empiric method.

CONCLUSIONS

There was an association between the empiric method, percentage of calculated activity delivered to the patient, and the most severe toxicity, RILD. A predictive model for RILD is not yet possible given the large variance in these data.

Safety and efficacy of Y-90 microsphere treatment in patients with primary and metastatic liver cancer: the tumor selectivity of the treatment as a function of tumor to liver flow ratio

BACKGROUND

Treatment records and follow-up data on 40 patients with primary and metastatic liver malignancies who underwent a single whole-liver treatment with Y-90 resin microspheres (SIR-Spheres Sirtex Medical, Lake Forest, IL) were retrospectively reviewed. The objective of the study was to evaluate the anatomic and physiologic determinants of radiation dose distribution, and the dose response of tumor and liver toxicity in patients with liver malignancies who underwent hepatic arterial Y-90 resin microsphere treatment.

METHODS

Liver and tumor volume calculations were performed on pre-treatment CT scans. Fractional tumor and liver flow characteristics and lung shunt fractions were determined using hepatic arterial Tc-99m MAA imaging. Absorbed dose calculations were performed using the MIRD equations. Liver toxicity was assessed clinically and by liver function tests. Tumor response to therapy was assessed by CT and/or tumor markers.

RESULTS

Of the 40 patients, 5 had hepatocellular cancer (HCC), and 35 had metastatic liver tumors (15 colorectal cancer, 10 neuroendocrine tumors, 4 breast cancer, 2 lung cancer, 1 ovarian cancer, 1 endometrial cancer, and 2 unknown primary adenocarcinoma). All patients were treated in a salvage setting with a 3 to 80 week follow-up (mean: 19 weeks). Tumor volumes ranged from 15.0 to 984.2 cc (mean: 294.9 cc) and tumor to normal liver uptake ratios ranged from 2.8 to 15.4 (mean: 5.4). Average administered activity was 1.2 GBq (0.4 to 2.4 GBq). Liver absorbed doses ranged from 0.7 to 99.5 Gy (mean: 17.2 Gy). Tumor absorbed doses ranged from 40.1 to 494.8 Gy (mean: 121.5 Gy). None of the patients had clinical venoocclusive disease or therapy-induced liver failure. Seven patients (17.5 %) had transient and 7 patients (17.5 %) had persistent LFT abnormalities. There were 27 (67.5%) responders (complete response, partial response, and stable disease). Tumor response correlated with higher tumor flow ratio as measured by Tc-99m MAA imaging.

CONCLUSION

Doses up to 99.5 Gy to uninvolved liver are tolerated with no clinical venoocclusive disease or liver failure. The lowest tumor dose producing a detectable response is 40.1 Gy. The utilization of MAA-based imaging techniques to determine tumor and liver blood flow for clinical treatment planning and the calculation of administered activity may improve clinical outcomes.

Resin 90Y-microsphere brachytherapy for unresectable colorectal liver metastases: modern USA experience

PURPOSE

Salvage therapy for patients with unresectable colorectal liver metastases that were refractory to oxaliplatin and irinotecan was performed via radioactive microspheres. High doses of radiation were delivered to tumors from permanently implanted 90Y microspheres, delivered through the hepatic arterial vessels.

METHODS AND MATERIALS

Patients from 7 institutions were selected for treatment after screening-defined vascular access to all the tumors, and imaging-confirmed microspheres would be implanted only in the liver tumors. All patients were followed with laboratory and imaging studies at regular intervals until death. Toxicities, both acute and late, were recorded, and actuarial survival determined.

RESULTS

A total of 208 patients were treated from April 2002 to April 2005. Median follow-up of the 129 men and 79 women is 13 months (range, 1-42 months). Median survival is 10.5 months for responders but only 4.5 months in nonresponders. No treatment-related procedure deaths or radiation-related venoocclusive liver failures were found. Computed tomography partial response was 35%; positron emission tomography response of 91% and reduction in carcinoembryonic antigen of 70% were achieved.

CONCLUSIONS

In this group of heavily pretreated patients, radioactive microspheres produced an encouraging median survival, with acceptable toxicity, and a significant objective response rate, which suggests that further investigation of this approach is warranted.

Pathologic response and microdosimetry of (90)Y microspheres in man: review of four explanted whole livers

INTRODUCTION

Radioactive microsphere (90)Y therapy is increasingly used for primary and metastatic solid tumors in the liver. We present an analysis of 4 explanted livers previously treated with (90)Y microsphere agents (glass or resin). One tumor nodule was analyzed with submillimeter three-dimensional microdosimetry.

METHODS AND MATERIALS

Four patients received hepatic artery delivery of (90)Y microspheres for unresectable hepatocellular and colon cancers. Whole livers were explanted as part of lifesaving cadaveric transplant in 2 patients with hepatoma. These patients had received glass microspheres as a procedural bridge to transplant. Autopsy was performed on 2 patients with colon cancer who died of progressive metastatic disease and who had been treated with resin microspheres. Complete pathologic review was performed on each whole liver, including estimation of the response of the tumor to therapy, distribution of microspheres in the tumor and normal liver tissues, and normal-tissue radiation response. A biopsy taken from the edge of a tumor nodule was sectioned serially for three-dimensional radiation dosimetry analyses. Three-dimensional microsphere coordinates within the biopsy specimen were used to calculate dosage using a three-dimensional dose kernel. Isodose coverage of tumor and normal liver areas and total dose delivered were determined.

RESULTS

Preferential and heterogeneous deposition of microspheres was noted at the edge of tumor nodules compared with the center portion of the tumor or normal liver parenchyma. Both glass and resin microspheres delivered high cumulative doses to the tumor, which varied from 100 Gy to more than 3000 Gy. No veno-occlusive disease or widespread radiation hepatitis was seen.

CONCLUSION

Microsphere ((90)Y) therapy delivers high numbers of spheres with resulting high total doses of radiation, preferentially in the periphery of tumors. Normal liver parenchyma showed little radiation effect away from the tumors. Heterogeneous high-dose regions in the tumor were produced by both glass and resin microspheres.

Internal radiotherapy for hepatic metastases II: The blood supply to hepatic metastases

Given that metastatic hepatic malignancy remains as a significant cause of death, with a median survival after diagnosis of only 7 months despite treatment, there exists a need for some effective treatment modality. Internal radiotherapy in the form of yttrium-90 microspheres infused into the hepatic artery appears to be a promising method of therapy. One criterion required for the success of this treatment is that of a differentially greater arterial supply to tumor as opposed to liver tissue. This arterial hypervascularity of tumor has been demonstrated before. However, some conflict has been reported as to the maintenance of this state as tumor size increases. Using 15 micrometers Cobalt-57 microspheres for studying salivary adenocarcinoma implants in DA rat livers, these experiments have demonstrated a constant blood flow in the tumor periphery of 3.9 times that within the normal hepatic parenchyma, regardless of tumor size. Also demonstrated is a progressive decrease in central tumor arterial blood flow after a tumor diameter of 6 mm has been exceeded. Arterial hypervascularity of liver tissue adjacent to the tumor has been demonstrated while an intermediate zone of liver tissue appeared hypovascular, suggesting the presence of shunting. In three humans with metastatic liver disease, hepatic artery infusion of particulate radiotracer has demonstrated the peripheral tumor hypervascularity and relative central tumor hypovascularity with good correlation obtained with the images of the metastases on conventional colloidal hepatic scintigraphy. This method allows assessment of the patient's suitability for internal radiotherapy by enabling assessment of the tumor vascularity and the degree of potentially dangerous extrahepatic irradiation.