Additional radiation absorbed dose estimates for Zevalin radioimmunotherapy

Biokinetics of Radiolabeled Monoclonal Antibody BC8: Differences in Biodistribution and Dosimetry Among Hematologic Malignancies

We reviewed ¹¹¹In-DOTA-anti-CD45 antibody (BC8) imaging and bone marrow biopsy measurements to ascertain the biodistribution and biokinetics of the radiolabeled antibody and to investigate differences based on type of hematologic malignancy. Methods: Serial whole-body scintigraphic images (4 time points) were obtained after infusion of the ¹¹¹In-DOTA-BC8 (176-406 MBq) into 52 adult patients with hematologic malignancies (lymphoma, multiple myeloma, acute myeloid leukemia, and myelodysplastic syndrome). Counts were obtained for the regions of interest for spleen, liver, kidneys, testicles (in men), and 2 marrow sites (acetabulum and sacrum), and correction for attenuation and background was made. Bone marrow biopsies were obtained 14-24 h after infusion, and the percentage of administered activity was determined. Absorbed radiation doses were calculated. Results: Initial uptake in liver averaged 32% ± 8.4% (SD) of administered activity (52 patients), which cleared monoexponentially with a biologic half-time of 293 ± 157 h (33 patients) or did not clear (19 patients). Initial uptake in spleen averaged 22% ± 12% and cleared with a biologic half-time of 271 ± 185 h (36 patients) or longer (6 patients). Initial uptake in kidney averaged 2.4% ± 2.0% and cleared with a biologic half-time of 243 ± 144 h (27 patients) or longer (9 patients). Initial uptake in red marrow averaged 23% ± 11% and cleared with a biologic half-time of 215 ± 107 h (43 patients) or longer (5 patients). Whole-body retention half-time averaged 198 ± 75 h. Splenic uptake was higher in the AML/MDS group than in the lymphoma group (P ≤ 0.05) or the multiple myeloma group (P ≤ 0.10). Liver represented the dose-limiting organ. For liver uptake, no significant differences were observed among the 3 malignancy groups. Average calculated radiation absorbed doses per unit of administered activity for a therapy infusion of ⁹⁰Y-DOTA-BC8 were 0.35 ± 0.20 cGy/MBq for red marrow, 0.80 ± 0.24 cGy/MBq for liver, 3.0 ± 1.4 cGy/MBq for spleen, 0.055 ± 0.014 cGy/MBq for total body, 0.21 ± 0.15 cGy/MBq for osteogenic cells, and 0.17 ± 0.15 cGy/MBq for kidneys. Conclusion: ¹¹¹In-DOTA-BC8 had a long retention time in liver, spleen, kidneys, and red marrow, and the highest absorbed doses were in spleen and liver. Few differences were observed by malignancy type. The exception was greater splenic uptake in the leukemia/MDS group than in the lymphoma or multiple myeloma group.

Radioimmunotherapy in Non-Hodgkin's Lymphoma: Retrospective Adverse Event Profiling of Zevalin and Bexxar

The development of monoclonal antibodies has dramatically changed the outcome of patients with non-Hodgkin’s lymphoma (NHL), the most common hematological malignancy. However, despite the satisfying results of monoclonal antibody treatment, only few NHL patients are permanently cured with single-agent therapies. In this context, radioimmunotherapy, the administration of radionuclides conjugated to monoclonal antibodies, is aimed to augment the single-agent efficacy of immunotherapy in order to deliver targeted radiation to tumors, particularly CD20+ B-cell lymphomas. Based on evidence from several trials in NHL, the radiolabeled antibodies ⁹⁰Y-ibritumomab tiuxetan (Zevalin, Spectrum Pharmaceuticals) and ¹³¹I-tositumomab (Bexxar, GlaxoSmithKline) received FDA approval in 2002 and 2003, respectively. However, none of the two radioimmunotherapeutic agents has been broadly applied in clinical practice. The main reason for the under-utilization of radioimmunotherapy includes economic and logistic considerations. However, concerns about potential side effects have also been raised. Driven by these developments, we performed retrospective analysis of adverse events reporting Zevalin or Bexxar, extracted from the FDA’s Adverse Event Reporting System (FAERS) and the World Health Organization’s VigiBase repository. Our results indicate that the two radioimmunotherapeutic agents have both related and distinct side effect profiles and confirm their known toxicological considerations. Our work also suggests that computational analysis of real-world post-marketing data can provide informative clinical insights. While more prospective studies are necessary to fully characterize the efficacy and safety of radioimmunotherapy, we expect that it has not yet reached its full therapeutic potential in modern hematological oncology.

90Y-ibritumomab tiuxetan therapy in allogeneic transplantation in B-cell lymphoma with extensive marrow involvement and chronic lymphocytic leukemia: utility of pretransplantation biodistribution

BACKGROUND

Biodistribution data to date using In-ibritumomab tiuxetan have been initially obtained in patients with less than 25% lymphomatous bone marrow involvement and adequate hematopoietic synthetic function. In this article we present the results of an analysis of the biodistribution data obtained from a cohort of patients with extensive bone marrow involvement, baseline cytopenias, and chronic lymphocytic leukemia (CLL).

MATERIALS AND METHODS

Thirty-nine patients with a diagnosis of B-cell lymphoma or CLL expressing the CD20 antigen, who had failed at least one prior regimen, and had evidence of persistent disease were included in this analysis; however, only 38 of them completed the treatment. Semiquantitative analysis of the biodistribution was performed using regions of interest over the liver, lungs, kidneys, spleen, and sacrum. The observed interpatient variability including higher liver uptake in four patients is discussed.

RESULTS

No severe solid organ toxicity was observed at the maximum administered activity of 1184 MBq (32 mCi) Y-ibritumomab tiuxetan. After accounting for differences in marrow involvement, patients with CLL exhibit comparable biodistributions to those with B-NHL. We found that the estimated sacral marrow uptake on 48 h images in patients with bone marrow involvement may be an indicator of bone marrow involvement. There was no correlation between tumor visualization and response to treatment.

CONCLUSION

These data suggest that the imaging step is not critical when the administered activity is below 1184 MBq (32 mCi). However, our analysis confirms that the semiquantitative imaging data can be used to identify patients at risk for liver toxicity when higher doses of Y-ibritumomab tiuxetan are used. Patients with CLL can have excellent targeting of disease by In-ibritumomab tiuxetan, indicating potential efficacy in this patient population.

Biodistribution and dosimetry of (131)I in thyroidectomy patients using semiquantitative gamma-camera imaging

The aim of this study was to determine the biodistribution, effective retention half-time (T(eff)), and internal organ dosimetry of (131)I administered to patients with papillary thyroid cancer after a total or near total thyroidectomy, and whole-body and organ activity was measured by gamma-camera imaging at 16 time points over 5 days following the administration of 1.1 GBq of (131)I in 5 patients. Whole-body scanning was performed by using a Siemens E-CAM() gamma-camera at a fixed distance of 5 cm from the patient. (131)I activity in regions of interest (ROIs) corresponding to the bladder, heart wall, kidneys, liver, lower gastrointestinal tract, lung, stomach, and thyroid remnants were measured, with measurements in the thigh used as the background. Most activity was localized to the lower gastrointestinal tract and thyroid remnants on day 1. The longest T(eff) was in the lung and the shortest was in the bladder (34.0 and 16.8 hours, respectively). The three organs with the highest absorbed doses per unit of administered activity were the lower gastrointestinal tract (2.03 mSv/MBq), the stomach (1.32 mSv/MBq), and the heart wall (1.24 mSv/MBq). T(eff) for thyroid remnants and the whole body were also estimated. We evaluated these organ doses to determine the normal tissues most likely at risk for stochastic and deterministic effects associated with (131)I therapy for thyroid cancer and benign disease. Our results represent preliminary findings, and the study will continue to accrue a greater number of study participants.

A theoretical dose-escalation study based on biological effective dose in radioimmunotherapy with (90)Y-ibritumomab tiuxetan (Zevalin)

AIM

To investigate the variation in biological effective dose (BED) produced by the uncertainty in absorbed dose and radiobiological parameters in Zevalin radioimmunotherapy.

METHODS

Eight patients scheduled for treatment with standard administration of (90)Y-ibritumomab tiuxetan (Zevalin) were studied. Patient-specific pretherapy dosimetry was performed by injection of (111)In-ibritumomab tiuxetan. Absorbed doses and BEDs were calculated for critical organs (COs) and tumours, assuming a 30% dose uncertainty and varying the radiobiological parameters in a reasonable range. In an activity-escalation study, BEDs for the COs were compared with the BED limits of external beam radiotherapy (EBRT) and BEDs for the tumour with the EBRT dose prescriptions.

RESULTS

At standard activities, the absorbed doses per unit activity for the COs were in agreement with those in the literature. Absorbed doses to lesions were rather variable, ranging from 1.47 to 16.7 Gy/GBq. Median tumour absorbed dose to lesions in the range 80-110 g was 9.6 Gy/GBq (range 9.2-16.7 Gy/GBq), yielding a mean BED of about 12 Gy for administration of 15 MBq/kg. For the administration of the myeloablative activity of 45 MBq/kg, risk of liver toxicity in one patient would have been foreseen by the model. Considering also the dose uncertainty, the potential risk of liver toxicity in one more patient, lung toxicity in one patient, and kidney toxicity in one patient would have been suggested. The absorbed dose uncertainty was found to be the main source of uncertainty in the BED. As for radiobiological parameters, at myeloablative activities, the increase in the repair half-time for sublethally damaged tissue (T(mu)) from 0.5 h to 5 h induced more consistent increases in mean BED/BED(limit) than alpha/beta variation from 2 Gy to 5 Gy: at 53 MBq/kg, 38% for the liver, and 34% for the lungs and kidneys (about threefold higher than that obtained for the increase alpha/beta).

CONCLUSION

At standard activities, absorbed doses to lesions appear to be effective, even though lower than prescribed by EBRT. At myeloablative dosages, the uncertainty associated with the absorbed doses and radiobiological parameters considerably affect BED evaluation and may account for possible "second-organ" toxicities.

Yttrium 90 ibritumomab tiuxetan in lymphoma

Radioimmunoconjugates are radioisotope-bound monoclonal antibodies that target radiation specifically to sites of lymphoma involvement. Initial studies of 90Y-ibritumomab tiuxetan in non-Hodgkin's lymphoma (NHL) have suggested benefit in patients with relapsed or refractory indolent disease. However, the routine adoption of this agent is tempered by concerns of associated toxicities and unclear long-term benefit. A comprehensive search for studies on 90Y-ibritumomab tiuxetan use in lymphoma was completed. The aims of this systematic review were to summarize and evaluate the evidence on: (1) the benefits and risks of this novel therapy; (2) predictors for response and toxicity; and (3) the role of dosimetry and imaging studies prior to treatment. A total of twenty trials investigating the use of 90Y-ibritumomab tiuxetan for the treatment of adult patients with NHL were identified. In trials of patients with relapsed or refractory indolent NHL, overall response rates ranged from 67 - 83%. In patients with follicular NHL refractory to the monoclonal antibody, rituximab, response rates remained high (74%). However, in rituximab-naïve patients with relapsed or refractory indolent or transformed NHL, the higher response rate seen with 90Y-ibritumomab tiuxetan therapy compared to rituximab monotherapy has not translated into clear improvements in time-to-progression or survival. 90Y-ibritumomab tiuxetan is an active agent in relapsed and refractory non-Hodgkin's lymphoma that should be considered in select patients.

MIRD dose estimate report No. 20: radiation absorbed-dose estimates for 111In- and 90Y-ibritumomab tiuxetan

Absorbed-dose calculations provide a scientific basis for evaluating the biologic effects associated with administered radiopharmaceuticals. In cancer therapy, radiation dosimetry supports treatment planning, dose-response analyses, predictions of therapy effectiveness, and completeness of patient medical records. In this study, we evaluated the organ radiation absorbed doses from intravenously administered (111)In- and (90)Y-ibritumomab tiuxetan.

METHODS

Ten patients (6 men and 4 women) with non-Hodgkin lymphoma, cared for at 3 different medical centers, were administered the tracer (111)In-ibritumomab tiuxetan and assessed using planar scintillation camera imaging at 5 time points and CT-organ volumetrics to determine patient-specific organ biokinetics and dosimetry. Explicit attenuation correction based on the transmission scan or transmission measurements provided the fraction of (111)In-administered activity in 7 major organs, the whole body, and remainder tissues over time through complete decay. Time-activity curves were constructed, and radiation doses were calculated using MIRD methods and implementing software.

RESULTS

Mean radiation absorbed doses for (111)In- and for (90)Y-ibritumomab tiuxetan administered to 10 cancer patients are reported for 24 organs and the whole body. Biologic uptake and retention data are given for 7 major source organs, remainder tissues, and the whole body. Median absorbed dose values calculated by this method were compared with previously published dosimetry for ibritumomab tiuxetan and the product package insert.

CONCLUSION

In high-dose radioimmunotherapy, the importance of patient-specific dosimetry becomes obvious when the objective of treatment planning is to achieve disease cures, safely, by limiting radiation dose to any critical normal organ to its maximum tolerable value. Compared with the current package insert, we found differences in median absorbed dose by multiples of 24 in the kidneys, 1.8 in the red marrow, 0.65 in the liver, 0.077 in the intestinal wall, 0.30 in the lungs, 0.46 in the spleen, and 0.34 in the heart wall.

[Contribution of radioimmunotherapy to the treatment of lymphoma]

Radioimmunotherapy (RIT) is an emerging treatment option for non-Hodgkin's lymphoma. Only Zevalin (Bayer Schering Pharma) radiolabeled with yttrium 90 ((90)Y) is approved in France for the treatment of adult patients with rituximab relapsed or refractory CD20+ follicular B-cell non-Hodgkin's lymphoma. This radioimmunotherapeutic agent consists of ibritumomab, a murine anti-CD20 monoclonal antibody, conjugated to the metal chelator tiuxetan for retention of the beta emitter (90)Y. This review presents the concept of RIT. The pharmacological characteristics of [(90)Y]-ibritumomab tiuxetan, the specificity of its preparation and its special precautions for use will be described. The other radionuclides and antibodies in development will also be mentioned.

Imaging of the distribution of (90)y-ibritumomab tiuxetan in bone marrow and comparison with pathology

PURPOSE

Radioimmunotherapy with anti-CD20 antibodies (Abs) labeled with beta-emitters is now used in the treatment of non-Hodgkin's lymphoma (NHL). Because (90)Y is a pure beta-emitter, no direct image of its distribution can be obtained in humans. In this paper, we present in this study imaging data of (90)Y-Ab distribution in human-mantle-cell lymphoma within a mouse model. Describing the actual distribution of the radionuclide at the level of particles range may have important impact on patient dosimetry and therapy treatment planning.

EXPERIMENTAL DESIGN

NOD/SCID mice were grafted with a human NHL cell line that involves the bone marrow. The mice were treated with (90)Y-ibritumomab tiuxetan (Zevalin); Schering AG, Germany) and sacrificed 2 hours after Zevalin administration. Tissue sections were then prepared and viewed under conventional microscopy. The distribution of the radioactivity in mouse femur was determined by using digital autoradiography and subsequently correlated with immunohistochemical results.

RESULTS

Various extent of bone marrow infiltration was investigated and found to be reproducible. Zevalin uptake was heterogeneous within the bone marrow. However, unspecific mouse monoclonal uptake by accessory myeloid cells gave nonspecific background radioactivity. Treating mice with an irrelevant mouse IgG1 monoclonal antibody (mAb) before Zevalin injection controlled this unspecific uptake, and images were strongly correlated with bone marrow infiltration on histologic analysis.

CONCLUSIONS

Our model was reproducible, and allows for the study of various bone marrow involvement with good sensitivity. We demonstrated that imaging of the beta-emitter was possible with good image quality and that (90)Y-Zevalin is distributed heterogeneously within bone marrow. These data suggest that detailed pharmacokinetics may be developed with this model.

Report of a European consensus workshop to develop recommendations for the optimal use of 90Y-ibritumomab tiuxetan (Zevalin®) in lymphoma

BACKGROUND

Non-Hodgkin's lymphoma (NHL) comprises a group of related haematological malignancies, predominantly of B-cell origin, which have been described as indolent or aggressive according to their clinical course. Standard treatment for indolent NHL consists of conventional chemotherapy, but, although long-term remissions may occur, most patients will die of their disease. Radioimmunotherapy (RIT) is a novel modality for treating indolent NHL, using monoclonal antibodies to target tumour cells with systemic, low-dose radiation. (90)Y-Ibritumomab tiuxetan (Zevalin); Schering AG, Berlin, Germany), the first RIT approved for use in relapsed/refractory indolent NHL, comprises the murine anti-CD20 monoclonal antibody ibritumomab, covalently linked to the high-energy beta-emitter, yttrium-90, by the chelator, tiuxetan.

MATERIALS AND METHODS

A multidisciplinary consensus workshop of European clinicians who had taken part in clinical trials of (90)Y-ibritumomab tiuxetan was convened to develop recommendations for the clinical preparation and administration of (90)Y-ibritumomab tiuxetan in Europe. The workshop was held in anticipation of European Medicines Agency approval of this agent, which was gained in 2004 for adult patients with rituximab-relapsed or refractory CD20(+) follicular B-cell NHL.

RESULTS AND CONCLUSIONS

This article summarises the consensus recommendations developed for hemato-oncologists.

Molecular Nuclear Imaging: The Radiopharmaceuticals (Review)

Application of the nuclear approach for the detection of inherited diseases is an important goal for nuclear medicine and will likely result in an important breakthrough, which will, hopefully, lead to improved diagnoses of genetic defects and objective evaluations of the efficacy of therapeutic strategies. Although still largely in the research realm, molecular imaging is in the process of emerging as a vital component of the diagnosis of disease and monitoring of the therapy. The clinical research in nuclear medicine has made major advancements in the direction of molecular medicine and targeted therapy. In the past few years, exponential achievements have been accomplished in the development of molecular nuclear imaging agents, as described below.

Testicular Uptake and Radiation Dose in Patients Receiving Zevalin™ and Pretarget™ CC49Fusion Protein

OBJECTIVE

Radiation dose to the testes from radionuclide therapies is of concern. This study evaluated image-quantification methods for testicular uptake in a phantom and in patients.

METHODS

A 50-mL vial and a large water tank were used to simulate testes and the body, respectively. Activity concentration in the vial and water tank was prepared to generate testes-to-background concentrations of 1.3 and 1.1. Five male lymphoma patients who received a Zevalin (Biogen Idec, Cambridge, MA) regimen and 6 male colorectal cancer patients who received a Pretarget (Neo Rx, Seattle, WA) CC49Fusion protein were evaluated. Testicular activity was quantified using two methods: (1) geometric-mean, background-corrected testicular region of interest (ROI) counts as a fraction of body counts without explicit attenuation correction (Zevalin Kit); (2) background-corrected anterior testicular ROI counts with attenuation correction using known depth in the phantom and CT depth in patients.

RESULTS

In the phantom study, Method 1 underestimated 49% and 39%, at image contrast of 1.3 and 1.1, respectively. Quantification was improved using Method 2 (7% for a 1.3 contrast, -17% for a 1.1 contrast). Method 2 was used in patients because background-corrected posterior ROI counts were statistically unreliable due to poor image contrast. In patients receiving Zevalin, the median peak percent injected dose (%ID)/testis was 0.10 (range, 0.08-0.18) with a median biologic half-time (T(bio1/2)) of 156 (range, 91-4200) hours. The median dose was 2.4 (range, 1.5-3.6) Gy/GBq, compared to the originally reported mean dose of 9.1 (range, 5.4-11.4) Gy/GBq (Zevalin package insert). In patients receiving the Pretarget CC49Fusion protein, the median peak %ID/testis was 0.22 (range, 0.05-0.29) with a median T(bio1/2) of 44 (range, 37-64) hours. The median dose was 0.84 (range, 0.3-1.2) Gy/GBq.

CONCLUSION

This study found that testicular doses from Zevalin were much lower than that originally reported in the package insert. The median testicular dose from Pretarget CC49Fusion protein was less than half that of the median testicular dose from Zevalin.

Radioimmunotherapy of non-Hodgkin’s lymphoma: Clinical development of the Zevalin regimen

Zevalin (ibritumomab tiuxetan; IDEC Pharmaceuticals Corporation, San Diego, CA, USA) was approved by the United States Food and Drug Administration on February 19, 2002, following 9 years of clinical development. Six clinical studies supported the Zevalin Biologics License Application. The Zevalin regimen is indicated for the treatment of patients with relapsed or refractory low-grade, follicular, or transformed B-cell non-Hodgkin's lymphoma (NHL), and for those with follicular NHL refractory to Rituxan (rituximab, MabThera; IDEC Pharmaceuticals Corporation, San Diego, CA and Genentech, South San Francisco, CA). In the year following FDA approval, approximately 1300 patients were treated in clinical trials or with the commercially available product.