Statistical assessment of treatment response in a cancer patient based on pre-therapy and post-therapy FDG-PET scans

This work arises from consideration of sarcoma patients in which fluorodeoxyglucose positron emission tomography (FDG-PET) imaging pre-therapy and post-chemotherapy is used to assess treatment response. Our focus is on methods for evaluation of the statistical uncertainty in the measured response for an individual patient. The gamma distribution is often used to describe data with constant coefficient of variation, but it can be adapted to describe the pseudo-Poisson character of PET measurements. We propose co-registering the pre-therapy and post- therapy images and modeling the approximately paired voxel-level data using the gamma statistics. Expressions for the estimation of the treatment effect and its variability are provided. Simulation studies explore the performance in the context of testing for a treatment effect. The impact of misregistration errors and how test power is affected by estimation of variability using simplified sampling assumptions, as might be produced by direct bootstrapping, is also clarified. The results illustrate a marked benefit in using a properly constructed paired approach. Remarkably, the power of the paired analysis is maintained even if the pre-image and post- image data are poorly registered. A theoretical explanation for this is indicated. The methodology is further illustrated in the context of a series of fluorodeoxyglucose-PET sarcoma patient studies. These data demonstrate the additional prognostic value of the proposed treatment effect test statistic. Copyright © 2016 John Wiley & Sons, Ltd.

Abstract P6-04-03: Changes in breast tumor metabolism and estradiol binding as measured by FES PET in patients treated with the histone deacetylace inhibitor vorinostat and aromatase inhibitor therapy

Background: Some estrogen receptor-positive (ER+) metastatic breast cancers are bone and soft tissue dominant, indolent, and controlled by endocrine therapy. However, these tumors eventually become refractory to endocrine therapy and need a mechanism to reset the “estrogen-dependence” to allow continued benefit upon progression. Histone deacetylase inhibitors (HDACi) act as modulators of gene expression that are promising therapeutic agents for this group of tumors (Huang 2000, Sabnis 2011). Preclinical and clinical data demonstrate in ER-poor tumors and cell lines ER up-regulation and consequently enhanced lethality to endocrine agents. The optimal dose and schedule are not known, but two promising phase II studies show benefit in a continuous schedule (Yardley 2011, Munster 2011). FES PET is a promising imaging agent used as a biomarker to determine which patients will benefit from endocrine therapy, and to monitor estradiol binding during therapy (Mortimer 2001, Linden 2011).

Methods: Patients with ER+ HER2− metastatic breast cancer with prior aromatase inhibitor (AI) exposure and clinical benefit of endocrine therapy were eligible for a phase II study of HDACi therapy to restore sensitivity to AI therapy. Following baseline FDG PET, FES PET and standard imaging (CT, MRI, ultrasound and/or bone scan as indicated by tumor location), patients received 2 weeks of vorinostat therapy (400 mg po daily). FES PET was performed at 2 weeks while on HDACi therapy. Patients then received 6 weeks of AI monotherapy. FDG PET, FES PET and response assessment were performed at 8 weeks. Patients with clinical benefit (stable disease or response) continued on the regimen, 2 weeks of vorinostat followed by 6 weeks of AI.

Results: To date, 8 patients have been enrolled of whom 6 have completed the first 8 weeks of treatment and all correlative imaging studies. FES biomarker imaging results are mixed, with some patients showing an increase in tumor estradiol concentrating ability by FES PET on HDACi therapy, and decline in metabolic activity by FDG. Two patients continue on treatment with clinical benefit. Results will be updated as accrual continues.

Conclusions: Changes in estradiol binding are measured by serial FES PET in patients on HDACi therapy support preclinical concept of HDACi modulation of ER expression in metastatic breast cancer. Molecular imaging is a promising tool to monitor Estradiol binding pharmacodynamics, and Vorinostat HDACi therapy is a promising novel approach to allow patients to avoid toxicities of traditional chemotherapy once their tumor has progressed on endocrine therapy.

Funding: P01, MKA, Merck

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-04-03.

A statistical modeling approach to the analysis of spatial patterns of FDG-PET uptake in human sarcoma

Clinical experience with positron emission tomography (PET) scanning of sarcoma, using fluorodeoxyglucose (FDG), has established spatial heterogeneity in the standardized uptake values within the tumor mass as a key prognostic indicator of patient survival. But it may be that a more detailed quantitation of the tumor FDG uptake pattern could provide additional insights into risk. The present work develops a statistical model for this purpose. The approach is based on a tubular representation of the tumor mass with a simplified radial analysis of uptake, transverse to the tubular axis. The technique provides novel ways of characterizing the overall profile of the tumor, including the introduction of an approach for the measurement of its phase of development. The phase measure can distinguish between early phase tumors, in which the uptake is highest at the core, and later stage masses, in which there can often be central voids in FDG uptake. Biologically, these voids arise from necrosis and fluid, fat or cartilage accumulations. The tumor profiling technique is implemented using open-source software tools and illustrations are provided with clinically representative scans. A series of FDG-PET studies from 185 patients is used to formally evaluate the prognostic benefit. Significant improvements in the prediction of patient survival and progression are obtained from the tumor profiling analysis. After adjustment for other factors including heterogeneity, a typical one standard deviation increase in phase (as determined by the analysis) is associated with close to 20% more risk of progression or death. The work confirms that more detailed quantitative assessments of the spatial pattern of PET imaging data of tumor masses, beyond the maximum FDG uptake (SUV(max)) and previously considered measures of heterogeneity, provide improved prognostic information for potential input to treatment decisions for future patients.

Imaging guidelines for children with Ewing sarcoma and osteosarcoma: a report from the Children's Oncology Group Bone Tumor Committee

The Children's Oncology Group (COG) is a multi-institutional cooperative group dedicated to childhood cancer research that has helped to increase the survival of children with cancer through clinical trials. These clinical trials include a standardized regimen of imaging examinations performed prior to, during, and following therapy. This article presents imaging guidelines developed by a multidisciplinary group from the COG Bone Tumor Committee. These guidelines provide both required and recommended studies. Recommended examinations may become required in the future. These guidelines should be considered a work in progress that will evolve with advances in imaging and childhood cancer research.

Risk assessment in high grade sarcoma patients during neoadjuvant chemotherapy using multiple tracer PET

20006

Background: Patients with high grade soft tissue sarcomas are treated with neoadjuvant chemotherapy. Sarcomas have biological features that may predict for poor outcome. Some of these features are tumor proliferation rate, level of tumor hypoxia, and upregulation of tumor drug resistance mechanisms. Methods: We have a group of specific PET imaging agents to quantify the level of activity of these tumor processes. Patients with soft tissue sarcomas receive [C-11]Thymidine (TdR) to assess cellular proliferation, [O-15] Water to quantify tumor blood flow and to serve as the input function for quantification of the other tracers, [C-11]Verapamil to assess drug resistance mechanism activity, and [F-18]Fluoromisonidazole) FMISO to quantify changes in tumor hypoxic volume in response to treatment. These studies are performed in a single PET imaging session prior to neoadjuvant chemotherapy, after the second of four cycles of therapy and in the week prior to resection. Results: An example of this complex study result, is demonstrated by a recent patient with a high grade soft tissue sarcoma. The tumor showed increased TdR uptake, a moderate hypoxic volume, and [C-11] verapamil uptake prior to initiation of neoadjuvant adriamycin based chemotherapy. After 2 cycles of therapy, there was a significant decrease in the maximum level and volume of TdR uptake and a large reduction in tumor hypoxic volume. Conclusions: These data would imply a high risk soft tissue sarcoma due the presence of increased cellular proliferation, a significant hypoxic volume and the absence of p-glycoprotein activity determined by the presence of [C-11]Verapamil uptake. However, early response is also suggested by the findings above. Patient outcome will be assessed and correlated with these tumor parameters to further understand what tumor biological risk factors can be quantified non-invasively and repeated throughout the clinical course in soft tissue sarcoma patients. Supported by NIH NCI PO1 42045–18 and S10 RR017229–01

[Table: see text]

No significant financial relationships to disclose.

[(18)F]FMISO and [(18)F]FDG PET imaging in soft tissue sarcomas: correlation of hypoxia, metabolism and VEGF expression

Hypoxia imparts resistance to radiotherapy and chemotherapy and also promotes a variety of changes in tumor biology through inducible promoters. The purpose of this study was to evaluate the use of positron emission tomography (PET) imaging with fluorine-18 fluoromisonidazole (FMISO) in soft tissue sarcomas (STS) as a measure of hypoxia and to compare the results with those obtained using [(18)F]fluorodeoxyglucose (FDG) and other known biologic correlates. FDG evaluates energy metabolism in tumors while FMISO uptake is proportional to tissue hypoxia. FMISO uptake was compared with FDG uptake. Vascular endothelial growth factor (VEGF) expression was also compared with FMISO uptake. Nineteen patients with STS underwent PET scanning with quantitative determination of FMISO and FDG uptake prior to therapy (neo-adjuvant chemotherapy or surgery alone). Ten patients receiving neo-adjuvant chemotherapy were also imaged after chemotherapy but prior to surgical resection. Standardized uptake value (SUV) was used to describe FDG uptake; regional tissue to blood ratio (>or=1.2 was considered significant) was used for FMISO uptake. Significant hypoxia was found in 76% of tumors imaged prior to therapy. No correlation was identified between pretherapy hypoxic volume (HV) and tumor grade ( r=0.15) or tumor volume ( r=0.03). The correlation of HV with VEGF expression was 0.39. Individual tumors showed marked heterogeneity in regional VEGF expression. The mean pixel-by-pixel correlation between FMISO and FDG uptake was 0.49 (range 0.09-0.79) pretreatment and 0.32 (range -0.46-0.72) after treatment. Most tumors showed evidence of reduced uptake of both FMISO and FDG following chemotherapy. FMISO PET demonstrates areas of significant and heterogeneous hypoxia in soft tissue sarcomas. The significant discrepancy between FDG and FMISO uptake seen in this study indicates that regional hypoxia and glucose metabolism do not always correlate. Similarly, we did not find any relationship between the hypoxic volume and the tumor volume or VEGF expression. Identification of hypoxia and development of a more complete biologic profile of STS will serve to guide more rational, individualized cancer treatment approaches.

18fluorodeoxyglucose positron emission tomography to detect mediastinal or internal mammary metastases in breast cancer

PURPOSE

To determine the prevalence of suspected disease in the mediastinum and internal mammary (IM) node chain by 18fluorodeoxyglucose (FDG) positron emission tomography (PET), compared with conventional staging by computed tomography (CT) in patients with recurrent or metastatic breast cancer.

PATIENTS AND METHODS

We retrospectively evaluated intrathoracic lymph nodes using FDG PET and CT data in 73 consecutive patients with recurrent or metastatic breast cancer who had both CT and FDG PET within 30 days of each other. In reviews of CT scans, mediastinal nodes measuring 1 cm or greater in the short axis were considered positive. PET was considered positive when there were one or more mediastinal foci of FDG uptake greater than the mediastinal blood pool.

RESULTS

Overall, 40% of patients had abnormal mediastinal or IM FDG uptake consistent with metastases, compared with 23% of patients who had suspiciously enlarged mediastinal or IM nodes by CT. Both FDG PET and CT were positive in 22%. In the subset of 33 patients with assessable follow-up by CT or biopsy, the sensitivity, specificity, and accuracy for nodal disease was 85%, 90%, and 88%, respectively, by FDG PET; 54%, 85%, and 73%, respectively, by prospective interpretation of CT; and 50%, 83%, and 70%, respectively, by blinded observer interpretation of CT. Among patients suspected of having only locoregional disease recurrence (n = 33), 10 had unsuspected mediastinal or IM disease by FDG PET.

CONCLUSION

FDG PET may uncover disease in these nodal regions not recognized by conventional staging methods. Future prospective studies using histopathology for confirmation are needed to validate the preliminary findings of this retrospective study.

Imaging cellular proliferation as a measure of response to therapy

Cell proliferation imaging is based on extensive laboratory investigations of labeled thymidine being selectively incorporated into DNA. [11C]-Thymidine labeled in the ring-2 or the methyl position is the natural extension of earlier work using tritiated thymidine. Proliferation imaging using [11C]-thymidine requires correction for labeled metabolites; however, quantitative approaches can provide reliable estimates of cellular proliferation by measuring thymidine flux from the blood into DNA in tumors. 18F-labeled thymidine analogs that are resistant to catabolism in vivo, [18F]-FLT and [18F]-FMAU, may simplify quantitative analysis and may be more suitable for clinical studies but will require careful validation to determine how their uptake is quantitatively related to cell growth. Clinical studies using [11C]-thymidine have demonstrated the power of cellular proliferation imaging to characterize tumors and monitor response early in the course of therapy. Patient imaging using the PET thymidine analogs is at an earlier stage but appears promising as a clinically feasible approach to cellular proliferation imaging.

Internal mammary lymph node drainage patterns in patients with breast cancer documented by breast lymphoscintigraphy

BACKGROUND

Metastases to internal mammary lymph nodes (IMN) may occur in patients with breast cancer and may alter treatment recommendations. The purpose of this study was to identify the frequency of IMN drainage in patients undergoing breast lymphoscintigraphy and sentinel lymph node dissection (SLND).

METHODS

The combined technique of peritumoral injection of radiocolloid and Lymphazurin blue for SLND was performed on 220 patients. All patients underwent preoperative lymphoscintigraphy before SLND. Lesion location by quadrant included: 110 upper outer (UOQ), 49 lower outer (LOQ), 30 upper inner (UIQ), 24 lower inner (LIQ), and 7 central.

RESULTS

Drainage to any nodal basin was observed in 184 of 220 patients (84%). IMN drainage was documented in 37 of 220 (17%) of patients. IMN drainage without evidence of axillary drainage occurred in 2 of 220 patients(1%). Drainage to the IMN based on quadrant location of the lesion was as follows: UOQ, 10%; LOQ, 27%; UIQ, 17%; LIQ, 25%; and central, 29%.

CONCLUSIONS

Internal mammary lymph node drainage shown by breast lymphoscintigraphy is common. Tumors in all quadrants may drain to IMNs, although drainage is significantly more common from quadrants other than the UOQ. Further studies are needed to determine whether lymphoscintigraphy drainage patterns identify patients at the highest risk for IMN metastases who may benefit from radiotherapy.

Increased false negative sentinel node biopsy rates after preoperative chemotherapy for invasive breast carcinoma

BACKGROUND

Sentinel lymph node dissection (SLND) has been a promising new technique in breast carcinoma staging, but could be unreliable in certain patient subsets. The current study assessed whether age, preoperative chemotherapy, tumor size, and/or previous excisional biopsy influenced the identification of sentinel nodes (SLNs) or the reliability of a node-negative SLND in predicting a node negative axilla.

METHODS

Eighty-two patients who had clinically negative axillae underwent SLND followed by Level I/II axillary lymph node dissection (ALND). SLNDs were performed using both technetium-99m (Tc-99m) labeled colloid and isosulfan blue dye. SLNs were analyzed by hematoxlyin and eosin and immunocytochemical techniques.

RESULTS

SLNs were successfully identified in 80% of patients. Mapping success was decreased among postmenopausal women but was not influenced by preoperative chemotherapy, large tumor size, or previous excisional biopsy. Of the 31 successfully mapped, node positive patients, 5 had false negative (FN) SLNDs (overall FN rate = 16%). Of the 9 successfully mapped patients who had received preoperative chemotherapy and had positive axillary nodes, 3 had FN SLND (FN rate = 33%). The presence of clinically positive lymph nodes before chemotherapy did not predict which patients would have a subsequent FN SLND. T3 tumor size, but not previous excision, was associated significantly with increased FN rate, although the FN rate for previous excision was 11%. No FN SLND occurred with T1/T2 tumors that were not excised previously and had not received preoperative chemotherapy.

CONCLUSIONS

Preoperative chemotherapy was associated with an unacceptably high FN rate for SLND. While larger tumor size also was associated with FN SLND, this effect might have been due to preoperative chemotherapy use in these patients. Small sample size precluded determining whether excisional biopsy before mapping increased FN SLND rates independently.

A phase I/II trial of iodine-131-tositumomab (anti-CD20), etoposide, cyclophosphamide, and autologous stem cell transplantation for relapsed B-cell lymphomas

Relapsed B-cell lymphomas are incurable with conventional chemotherapy and radiation therapy, although a fraction of patients can be cured with high-dose chemoradiotherapy and autologous stem-cell transplantation (ASCT). We conducted a phase I/II trial to estimate the maximum tolerated dose (MTD) of iodine 131 ((131)I)-tositumomab (anti-CD20 antibody) that could be combined with etoposide and cyclophosphamide followed by ASCT in patients with relapsed B-cell lymphomas. Fifty-two patients received a trace-labeled infusion of 1.7 mg/kg (131)I-tositumomab (185-370 MBq) followed by serial quantitative gamma-camera imaging and estimation of absorbed doses of radiation to tumor sites and normal organs. Ten days later, patients received a therapeutic infusion of 1.7 mg/kg tositumomab labeled with an amount of (131)I calculated to deliver the target dose of radiation (20-27 Gy) to critical normal organs (liver, kidneys, and lungs). Patients were maintained in radiation isolation until their total-body radioactivity was less than 0.07 mSv/h at 1 m. They were then given etoposide and cyclophosphamide followed by ASCT. The MTD of (131)I-tositumomab that could be safely combined with 60 mg/kg etoposide and 100 mg/kg cyclophosphamide delivered 25 Gy to critical normal organs. The estimated overall survival (OS) and progression-free survival (PFS) of all treated patients at 2 years was 83% and 68%, respectively. These findings compare favorably with those in a nonrandomized control group of patients who underwent transplantation, external-beam total-body irradiation, and etoposide and cyclophosphamide therapy during the same period (OS of 53% and PFS of 36% at 2 years), even after adjustment for confounding variables in a multivariable analysis.

(F-18) fluorodeoxyglucose positron emission tomography as a predictor of pathologic grade and other prognostic variables in bone and soft tissue sarcoma

Positron emission tomography (PET) can be used to measure tumor metabolism in sarcomas by measuring the standard uptake value (SUV) of (F-18) fluorodeoxyglucose (FDG). FDG-PET SUV has been shown to correlate with histological grade. We compared FDG-PET SUV in 89 bone and soft tissue sarcomas with histopathological features, including tumor grade, as well as with markers of cell proliferation and cell cycle regulatory gene expression that may be prognostically or therapeutically important. All patients had undergone PET before biopsy. Features evaluated included grade (National Cancer Institute for soft tissue or Mayo Clinic for bone), cellularity, and the number of mitoses per 10 400x fields. Deparaffinized, formalin-fixed sections were immunostained with antibodies to Ki-67 (MIB-1), p53 (DO7), p21WAF1 (EA10), and mdm-2 (1B10). For Ki-67, results were estimated as a percentage of positive cells. For p53 and mdm-2, only cases with >20% positive cells were considered to be overexpressing these proteins. For p21WAF1, only cases with <10% positive cells were considered to have lost normal p21WAF1 expression. Tumor S-phase percentage and ploidy were determined by flow cytometry. FDG-PET SUV was associated with histopathological grade, cellularity, mitotic activity, MIB labeling index, and p53 overexpression. No association was seen with p21WAF1, mdm-2, S-phase fraction, or ploidy. Tumor metabolism data acquired by FDG-PET may help ensure accurate grading and prognostication in sarcoma by guiding biopsy toward the most biologically significant regions of large masses. Further follow-up will be necessary to determine whether FDG-PET provides independent prognostic information.

Sentinel lymph node mapping for breast cancer: analysis in a diverse patient group

PURPOSE

To evaluate sentinel lymph node mapping in patients with breast cancer.

MATERIALS AND METHODS

Sixty-two patients with breast cancer scheduled to undergo axillary nodal dissection underwent scintigraphic localization of sentinel lymph nodes with filtered technetium 99m sulfur colloid. At surgery, isosulfan blue was injected. Sentinel nodes were identifiable by blue color and by radioactivity with hand-held gamma probe. Results were analyzed statistically.

RESULTS

A sentinel lymph node was identified in 49 patients (79%). Lymph nodes were positive for metastatic disease in 26 patients (42%). The mapping success rate was 78% (n = 21) in the 27 patients with no prior surgery, 78% (n = 18) in the 23 patients with prior surgery, and 86% (n = 12) in the 14 patients with prior chemotherapy. Axillary nodes were positive in 11 (41%) of the 27 patients with no prior intervention, six (26%) of the 23 patients with prior surgery, and 10 (71%) of the 14 patients with prior chemotherapy. There were no false-negative findings in patients without prior intervention. Four patients with positive nodes had false-negative sentinel nodes.

CONCLUSION

Sentinel lymph node mapping and biopsy without axillary dissection is appropriate in patients with breast cancer who have not undergone prior intervention. Further study is necessary to ascertain the accuracy of the procedure for patients who have undergone presurgical chemotherapy or previous excisional biopsy.

Nuclear medicine in cancer diagnosis

Nuclear medicine imaging has contributed significantly to diagnosis, treatment planning, and the evaluation of response to treatment in patients with cancer since the development of modern techniques in the 1970s. Diagnostic applications such as the bone scan continue to be the most common use in oncology because of their high sensitivity but the contribution of nuclear medicine to oncology can perhaps be best understood in the context of patient management. Staging of newly presenting cancer patients and restaging for treatment planning are reviewed here. For treatment response and disease recurrence nuclear medicine provides information non-invasively. The studies can be repeated with few side-effects and with low radiation absorbed doses. Results can be directly correlated with clinical laboratory data. The goals of biologically characterising an individual patient's tumour and predicting his or her response to treatment are within reach.

Phase I study of (131)I-anti-CD45 antibody plus cyclophosphamide and total body irradiation for advanced acute leukemia and myelodysplastic syndrome

Delivery of targeted hematopoietic irradiation using radiolabeled monoclonal antibody may improve the outcome of marrow transplantation for advanced acute leukemia by decreasing relapse without increasing toxicity. We conducted a phase I study that examined the biodistribution of (131)I-labeled anti-CD45 antibody and determined the toxicity of escalating doses of targeted radiation combined with 120 mg/kg cyclophosphamide (CY) and 12 Gy total body irradiation (TBI) followed by HLA-matched related allogeneic or autologous transplant. Forty-four patients with advanced acute leukemia or myelodysplasia received a biodistribution dose of 0.5 mg/kg (131)I-BC8 (murine anti-CD45) antibody. The mean +/- SEM estimated radiation absorbed dose (centigray per millicurie of (131)I) delivered to bone marrow and spleen was 6.5 +/- 0.5 and 13.5 +/- 1.3, respectively, with liver, lung, kidney, and total body receiving lower amounts of 2.8 +/- 0.2, 1.8 +/- 0.1, 0.6 +/- 0.04, and 0.4 +/- 0.02, respectively. Thirty-seven patients (84%) had favorable biodistribution of antibody, with a higher estimated radiation absorbed dose to marrow and spleen than to normal organs. Thirty-four patients received a therapeutic dose of (131)I-antibody labeled with 76 to 612 mCi (131)I to deliver estimated radiation absorbed doses to liver (normal organ receiving the highest dose) of 3.5 Gy (level 1) to 12.25 Gy (level 6) in addition to CY and TBI. The maximum tolerated dose was level 5 (delivering 10.5 Gy to liver), with grade III/IV mucositis in 2 of 2 patients treated at level 6. Of 25 treated patients with acute myeloid leukemia (AML)/myelodysplastic syndrome (MDS), 7 survive disease-free 15 to 89 months (median, 65 months) posttransplant. Of 9 treated patients with acute lymphoblastic leukemia (ALL), 3 survive disease-free 19, 54, and 66 months posttransplant. We conclude that (131)I-anti-CD45 antibody can safely deliver substantial supplemental doses of radiation to bone marrow (approximately 24 Gy) and spleen (approximately 50 Gy) when combined with conventional CY/TBI.

Technical aspects of sentinel node lymphoscintigraphy for breast cancer

OBJECTIVE

A significant morbidity risk is associated with axillary nodal dissections for breast cancer. Many treatment decisions are based on axillary nodal status. Lymphatic mapping and sentinel node biopsy have been investigated to determine if the histology of the sentinel node reflects the remaining lymph node basin. We describe the technical aspects of sentinel node lymphoscintigraphy for breast cancer.

METHODS

Ninety-three patients had lymphoscintigraphy for breast cancer. Patients with palpable lesions had 4 concentric injections around the site and lesions requiring localization had injections made through tubing connected to the localizing wire introducer needle. Immediate static images were acquired and the sentinel node was marked for surgery. Marks were reverified using a handheld gamma probe.

RESULTS

Lymph nodes were visualized by lymphoscintigraphy in 87% of cases. Time to visualization of lymph nodes ranged from 1-120 min with a mean of 28 min. An average of 1.5 nodes were visualized. The overall success rate for identifying the sentinel node at time of surgery was 85%.

CONCLUSION

We conclude that lymphoscintigraphy for breast cancer is a detailed procedure that requires coordination with radiology and surgery teams to ensure proper identification of sentinel lymph nodes.

Kinetic analysis of 2-[11C]thymidine PET imaging studies: validation studies

2-[11C]thymidine has been tested as a PET tracer of cellular proliferation. We have previously described a model of thymidine and labeled metabolite kinetics for use in quantifying the flux of thymidine into DNA as a measure of tumor proliferation. We describe here the results of studies to validate some of the model's assumptions and to test the model's ability to predict the time course of tracer incorporation into DNA in tumors.

METHODS

Three sets of studies were conducted: (a) The uptake of tracers in proliferative tissues of normal mice was measured early after injection to assess the relative delivery of thymidine and metabolites of thymidine catabolism (thymine and CO2) and calculate relative blood-tissue transfer rates (relative K1s). (b) By using sequential injections of [11C]thymidine and [11C]thymine in normal human volunteers, the kinetics of the first labeled metabolite were measured to determine whether it was trapped in proliferating tissue such as the bone marrow. (c) In a multitumor rat model, 2-[14C]thymidine injection, tumor sampling and quantitative DNA extraction were performed to measure the time course of label uptake into DNA for comparison with model predictions.

RESULTS

Studies in mice showed consistent relative delivery of thymidine and metabolites in somatic tissue but, as expected, showed reduced delivery of thymidine and thymine in the normal brain compared to CO2. Thymine studies in volunteers showed only minimal trapping of label in bone marrow in comparison to thymidine. This quantity of trapping could be explained by a small amount of fixation of labeled CO2 in tissue, a process that is included as part of the model. Uptake experiments in rats showed early incorporation of label into DNA, and the model was able to fit the time course of uptake.

CONCLUSION

These initial studies support the assumptions of the compartmental model and demonstrate its ability to quantify thymidine flux into DNA by using 2-[11C]thymidine and PET. Results suggest that further work will be necessary to investigate the effects of tumor heterogeneity and to compare PET measures of tumor proliferation to in vitro measures of proliferation and to clinical tumor behavior in patients undergoing therapy.

2-[C-11]thymidine imaging of malignant brain tumors

Malignant brain tumors pose diagnostic and therapeutic problems. Despite the advent of new brain imaging modalities, including magnetic resonance imaging (MRI) and [F-18]fluorodeoxyglucose (FDG) positron emission tomography (PET), determination of tumor viability and response to treatment is often difficult. Blood-brain barrier disruption can be caused by tumor or nonspecific reactions to treatment, making MRI interpretation ambiguous. The high metabolic background of the normal brain and its regional variability makes it difficult to identify small or less active tumors by FDG imaging of cellular energetics. We have investigated 2-[C-11]thymidine (dThd) and PET to image the rate of brain tumor cellular proliferation. A series of 13 patients underwent closely spaced dThd PET, FDG PET, and MRI procedures, and the image results were compared by standardized visual analysis. The resulting dThd scans were qualitatively different from the other two scans in approximately 50% of the cases, which suggests that dThd provided information distinct from FDG PET and MRI. In two cases, recurrent tumor was more apparent on the dThd study than on FDG; in two other patients, tumor dThd uptake was less than FDG uptake, and these patients had slower tumor progression than the three patients with both high dThd and FDG uptake. To better characterize tumor proliferation, kinetic modeling was applied to dynamic dThd PET uptake data and metabolite-analyzed blood data in a subset of patients. Kinetic analysis was able to remove the confounding influence of [C-11]CO2, the principal labeled metabolite of 2-[C-11]dThd, and to estimate the flux of dThd incorporation into DNA. Sequential, same-day [C-11]CO2 and [C-11]dThd imaging demonstrated the ability of kinetic analysis to model both dThd and CO2 simultaneously. Images of dThd flux obtained using the model along with the mixture analysis method for pixel-by-pixel parametric imaging significantly enhanced the contrast of tumor compared with normal brain. Comparison of model estimates of dThd transport versus dThd flux was able to discern increased dThd uptake simply on the basis of blood-brain barrier disruption retention on the basis of increased cellular proliferation. This preliminary study demonstrates the potential for imaging brain tumor cellular proliferation to provide unique information for guiding patient treatment.

Follow-up of relapsed B-cell lymphoma patients treated with iodine-131-labeled anti-CD20 antibody and autologous stem-cell rescue

PURPOSE

Radioimmunotherapy (RIT) is a promising treatment approach for B-cell lymphomas. This is our first opportunity to report long-term follow-up data and late toxicities in 29 patients treated with myeloablative doses of iodine-131-anti-CD20 antibody (anti-B1) and autologous stem-cell rescue.

PATIENTS AND METHODS

Trace-labeled biodistribution studies first determined the ability to deliver higher absorbed radiation doses to tumor sites than to lung, liver, or kidney at varying amounts of anti-B1 protein (0.35, 1.7, or 7 mg/kg). Twenty-nine patients received therapeutic infusions of single-agent (131)I-anti-B1, given at the protein dose found optimal in the biodistribution study, labeled with amounts of (131)I (280 to 785 mCi [10.4 to 29.0 GBq]) calculated to deliver specific absorbed radiation doses to the normal organs, followed by autologous stem-cell support.

RESULTS

Major responses occurred in 25 patients (86%), with 23 complete responses (CRs; 79%). The nonhematopoietic dose-limiting toxicity was reversible cardiopulmonary insufficiency, which occurred in two patients at RIT doses that delivered > or = 27 Gy to the lungs. With a median follow-up time of 42 months, the estimated overall and progression-free survival rates are 68% and 42%, respectively. Currently, 14 of 29 patients remain in unmaintained remissions that range from 27+ to 87+ months after RIT. Late toxicities have been uncommon except for elevated thyroid-stimulating hormone (TSH) levels found in approximately 60% of the subjects. Two patients developed second malignancies, but none have developed myelodysplasia (MDS).

CONCLUSION

Myeloablative (131)I-anti-B1 RIT is relatively well tolerated when given with autologous stem-cell support and often results in prolonged remission durations with few late toxicities.

Imaging of oncologic patients: benefit of combined CT and FDG PET in the diagnosis of malignancy

OBJECTIVE

The purpose of this study was to assess the benefit of combined CT and 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in diagnosing malignancy.

MATERIALS AND METHODS

The records of 26 patients with intraabdominal and intrathoracic neoplasms who underwent CT and FDG PET between January 1995 and September 1996 were retrospectively reviewed. Most of these patients had inconclusive findings on prior CT for the diagnosis of malignancy. Only sites of potential malignant disease were included in the data analysis. Presence or absence of malignancy was confirmed by histopathology or follow-up CT. Three observers experienced in abdominal imaging used CT findings alone to estimate level of suspicion (1 = definitely not malignant to 5 = definitely malignant) for primary or recurrent neoplasms (n = 21), distant metastases (n = 25), and neoplastic nodal involvement (n = 18). Six weeks later the three observers reviewed the same CT examinations supplemented with FDG PET and reestimated suspicion of malignancy. Receiver operating characteristic methodology was used to analyze the results. Sensitivity, specificity, positive and negative predictive values, and accuracy in diagnosis of malignant disease were calculated using level 4 (probable malignancy) as the cutoff for the presence of disease.

RESULTS

The mean area under the receiver operating characteristic curve, indicating successful diagnosis of malignancy, was .82 for CT alone and .92 for CT with FDG PET (p < .05). The accuracies for diagnosis of primary or recurrent neoplasms, distant metastases, and neoplastic nodal involvement were 62%, 68%, and 83%, respectively, for CT alone and 81% (p = .06), 88% (p = .03), and 89% (p > .25), respectively, for CT with FDG PET. Also, supplemental FDG PET imaging improved observer confidence and accuracy in diagnosing recurrent neoplasm in four (36%) of 11 patients who had undergone surgery or chemoradiation and in diagnosing four (29%) of 14 extrahepatic sites that had potential metastases.

CONCLUSION

Diagnosis of malignancy in oncologic patients is significantly improved when CT is supplemented with FDG PET. Combined imaging is particularly helpful in the evaluation of potential recurrence in previously treated patients and for diagnosing extrahepatic lesions that may be distant metastases.

Carbon-11-thymidine and FDG to measure therapy response

This study was performed to determine if PET imaging with 11C-thymidine could measure tumor response to chemotherapy early after the initiation of treatment. Imaging of deoxyriboneucleic acid biosynthesis, quantitated with 11C-thymidine, was compared with measurements of tumor energetics, obtained by imaging with 18F-fluorodeoxyglucose (FDG).

METHODS

We imaged four patients with small cell lung cancer and two with high-grade sarcoma both before and approximately 1 wk after the start of chemotherapy. Thymidine and FDG studies were done on the same day. Tumor uptake was quantified by standardized uptake values (SUVs) for both tracers by the metabolic rate of FDG and thymidine flux constant (K(TdR)) using regions of interest placed on the most active part of the tumor.

RESULTS

In the four patients with clinical response to treatment, both thymidine and FDG uptake markedly declined 1 wk after therapy. Thymidine measurements of SUV and K(TdR) declined by 64% +/- 15% and 84% +/- 33%, respectively. FDG SUV and the metabolic rate of FDG declined by 51% +/- 9% and 63% +/- 23%, respectively. In the patient with metastatic small cell lung cancer who had disease progression, the thymidine SUV decreased by only 8% (FDG not done). In a patient with abdominal sarcoma and progressive disease, thymidine SUV was essentially unchanged (declined by 3%), whereas FDG SUV increased by 69%.

CONCLUSION

Images show a decline in both cellular energetics and proliferative rate after successful chemotherapy. In the two patients with progressive disease, thymidine uptake was unchanged 1 wk after therapy. In our limited series, K(TdR) measurements showed a complete shutdown in tumor proliferation in patients in whom FDG showed a more limited decrease in glucose metabolism.

Kinetic analysis of 2-[carbon-11]thymidine PET imaging studies: compartmental model and mathematical analysis

Carbon-11-thymidine is a PET tracer of DNA synthesis and cellular proliferation. Quantitative analysis of [11C]thymidine images is complicated by the presence of significant quantities of labeled metabolites. Estimation of the rate of thymidine incorporation into DNA using [11C]thymidine requires a kinetic model that is capable of describing the behavior of thymidine and labeled metabolites.

METHODS

Based on previous studies with labeled thymidine, we constructed a five-compartment model describing the kinetic behavior of 2-[11C]thymidine and its labeled metabolites. In addition, we have performed a series of calculations and simulations to calculate the sensitivity and identifiability of model parameters to estimate the extent to which individual parameters can be estimated; to determine appropriate model constraints necessary for reproducible estimates of the constant describing flux of thymidine from the blood into DNA, i.e., thymidine flux constant; and to determine the potential accuracy of model parameter and thymidine flux constant estimates from PET imaging data.

RESULTS

The underlying assumptions in the thymidine compartmental model lead to a description of the thymidine flux constant for DNA incorporation in terms of model parameters. Sensitivity and identifiability analyses suggest that the model parameters pertaining to labeled metabolites will be difficult to estimate independently of the thymidine parameters. Exact evaluation of the kinetic parameters of the labeled metabolites is not the principal goal of this model. Simulations were performed that suggest that it is preferable to tightly constrain these parameters to preset values near the center of their expected ranges. Although it is difficult to estimate individual thymidine model parameters, the flux constant for incorporation into DNA can be accurately estimated (r > 0.9 for estimated versus true simulated flux constant). Flux constant estimates are not affected by modest levels of local degradation of thymidine that may occur in proliferating tissue.

CONCLUSION

By using a kinetic model for thymidine and labeled metabolites, it is possible to estimate the flux of thymidine uptake and incorporation into DNA and, thereby, noninvasively estimate regional cellular proliferation using [11C]thymidine and PET.

Quantitative [F-18]fluorodeoxyglucose positron emission tomography in pretreatment and grading of sarcoma

The purpose of this study was to determine the relationship between sarcoma tumor grade and the quantitative tumor metabolism value for [F-18]fluorodeoxyglucose (FDG) determined by positron emission tomography (PET) imaging. Seventy patients with bone or soft-tissue sarcomas underwent PET scanning with quantitative determination of tumor FDG metabolic rate (MRFDG) before treatment. MRFDG (micromol/g/min) for each tumor was compared with National Cancer Institute tumor grade, S-phase percentage, and percentage of aneuploidy of the tumor population. The pretreatment quantitative determination of tumor MRFDG by PET correlates strongly with tumor grade but not with the other selected histopathological tumor correlates. In addition, overlap of MRFDG PET values with tumor grade suggests that PET, an objective tumor measurement, may provide an alternative means of assessing tumor biological potential or may have the potential to overcome some of the limitations of traditional pathological evaluation. FDG PET can uniquely provide a metabolic profile of a diverse group of sarcomas noninvasively and provide clinically relevant tumor biological information.

Tumor metabolic rates in sarcoma using FDG PET

In a busy clinical environment, the arterial blood sampling and long imaging time used for the determination of tumor metabolic rates are not always feasible. In this study, the relationship of tumor standard uptake value (SUV) and metabolic rate of FDG (MRFDG) was investigated in a group of patients with sarcoma. To further investigate the implications of reducing blood sampling requirements for determining tumor metabolic rate, the relationship between FDG blood clearance, obtained from serial venous blood sampling and from a hybrid method of early cardiac blood pool imaging, and late venous blood sampling was analyzed.

METHODS

Comparisons of the sarcoma SUV and MRFDG obtained using graphical analysis, dynamic FDG imaging and venous blood sampling were made. Also, venous and hybrid blood time-activity curves were analyzed for similarity and for their effect on the estimated tumor metabolic rate.

RESULTS

For this group of patients with sarcoma (n = 42), the tumor SUV and MRFDG had a consistent relationship, with an overall correlation coefficient of 0.94. The MRFDG, determined by venous blood sampling, had a 6% average overestimate, compared to the same value obtained by the hybrid method of early blood pool imaging and late venous sampling.

CONCLUSION

Both the correlation of SUV and MRFDG and the hybrid blood pool/tumor imaging protocol provide clinically feasible methods for obtaining tumor metabolic rate information in a busy clinical PET service.

Importance of pre-treatment radiation absorbed dose estimation for radioimmunotherapy of non-Hodgkin's lymphoma

Non-Hodgkin's lymphoma I-131 radioimmunotherapy data were analyzed to determine whether a predictive relationship exists between radiation absorbed doses calculated from biodistribution studies and doses derived from patient size. Radioactivity treatment administrations scaled to patient size (MBq/kg or MBq/m2) or fixed MBq doses do not produce consistent radiation absorbed dose to critical organs. Treatment trials that do not provide dose estimates for critical normal organs are less likely to succeed in identifying a clinical role for radioimmunotherapy.

In vitro and in situ magnetic resonance imaging signal features of atherosclerotic plaque-associated lipids

The goal of this study was to evaluate magnetic resonance imaging (MRI) signal features of the different types of lipids found in human atherosclerotic plaques. A 1.5-T SIGNA scanner was used to acquire T1-, T2-, and proton density-weighted data at four different temperatures for individual lipids and lipid mixtures designed to replicate the proportions of lipids found in plaques. Individual lipids and lipid mixtures were scanned both in a test tube and after implantation in the media of normal porcine aortas. Each of the three broad classes of lipids (triglycerides, unesterified and esterified cholesterol, and phospholipids) had different and distinct MR signal patterns, which allowed discrimination of these classes of lipids in vitro. Further, lipid implantation studies demonstrated that these distinct MR signal patterns could be used to readily distinguish each lipid type from surrounding porcine aortic media. MR signals from lipid mixtures demonstrated marked regional heterogeneity, similar to the heterogeneous lipid distribution characteristic of human atherosclerotic plaques. In summary, MR signals from lipid mixtures that mimic plaque lipid proportions can be detected at body temperature, especially in those mixtures with an increased percentage of cholesteryl esters. These studies raise the possibility that with further advances in technology, MRI may become a useful tool for determining the lipid content and composition of human atherosclerotic plaques in vivo.

Analysis of blood clearance and labeled metabolites for the estrogen receptor tracer [F-18]-16 alpha-fluoroestradiol (FES)

[F-18] 16 alpha-Fluoroestradiol (FES) has been shown to be a tracer of estrogen receptor content in breast tumors; however, quantitative analysis of FES images is complicated by the rapid metabolism of the tracer in vivo. To optimize FES PET imaging studies and to provide an input function for the quantitative analysis of the tracer FES uptake in breast tumors, we studied the clearance and metabolism of FES in 15 breast cancer patients. FES clearance, protein binding, and metabolite production and limited assays to determine the identity of labeled metabolites were performed. These studies show that FES was rapidly cleared from the blood and metabolized; at 20 min only 20% of the circulating radioactivity was unmetabolized FES, and much of this was protein bound. The detectable metabolites in either blood or urine are conjugation products, largely the glucuronide and the sulfate of FES, and these are excreted through the kidneys at a rate comparable to their introduction into the circulation. After 20 min postinjection the blood levels of radioactivity remain fairly constant. Our results, the first report on human metabolites, are in close agreement with previous animal studies of FES metabolism. These studies show that because FES clearance is rapid and metabolite background is nearly constant, imaging starting at 20 to 30 min after injection may provide good visualization of estrogen-containing tissues. Labeled metabolites need to be accounted for in quantifying FES uptake.

Energy-based scatter corrections for scintillation camera images of iodine-131

The use of high-dose 131I antibody therapy requires accurate measurement of normal tissue uptake to optimize the therapeutic dose. One of the factors limiting the accuracy of such measurements is scatter and collimator septal penetration. This study evaluated two classes of energy-based scatter corrections for quantitative 131I imaging: window-based and spectrum-fitting.

METHODS

The window-based approaches estimate scatter from data in two or three energy windows placed on either side of the 364-keV photopeak using empirical weighting factors. A set of images from spheres in an elliptical phantom were used to evaluate each of the window-based corrections. The spectrum-fitting technique estimates detected scatter at each pixel by fitting the observed energy spectrum with a function that models the photopeak and scatter, and which incorporates the response function of the camera. This technique was evaluated using a set of Rollo phantom images.

RESULTS

All of the window-based methods performed significantly better than a single photopeak window (338-389 keV), but the weighting factors were found to depend on the object being imaged. For images contaminated with scatter, the spectrum-fitting method significantly improved quantitation over photopeak windowing. Little difference, however, between any of the methods was observed for images containing small amounts of scatter.

CONCLUSION

Most clinical 131I imaging protocols will benefit from qualitative and quantitative improvements provided by the spectrum-fitting scatter correction. The technique offers the practical advantage that it does not require phantom-based calibrations. Finally, our results suggest that septal penetration and scatter in the collimator and other detector-head components are important sources of error in quantitative 131I images.

Phase II trial of 131I-B1 (anti-CD20) antibody therapy with autologous stem cell transplantation for relapsed B cell lymphomas

25 patients with relapsed B-cell lymphomas were evaluated with trace labelled doses (2.5 mg/kg, 185-370 MBq [5-10 mCi]) of 131I-labelled anti-CD20 (B1) antibody in a phase II trial. 22 patients achieved 131I-B1 biodistributions delivering higher doses of radiation to tumour sites than to normal organs and 21 of these were treated with therapeutic infusions of 131I-B1 (12.765-29.045 GBq) followed by autologous haemopoietic stem cell reinfusion. 18 of the 21 treated patients had objective responses, including 16 complete remissions. One patient died of progressive lymphoma and one died of sepsis. Analysis of our phase I and II trials with 131I-labelled B1 reveal a progression-free survival of 62% and an overall survival of 93% with a median follow-up of 2 years. 131I-anti-CD20 (B1) antibody therapy produces complete responses of long duration in most patients with relapsed B-cell lymphomas when given at maximally tolerated doses with autologous stem cell rescue.

Development of a marrow transplant regimen for acute leukemia using targeted hematopoietic irradiation delivered by 131I-labeled anti-CD45 antibody, combined with cyclophosphamide and total body irradiation

In an attempt to decrease the relapse rate after bone marrow transplantation (BMT) for advanced acute leukemia, we initiated studies using 131I-labeled anti-CD45 antibody (BC8) to deliver radiation specifically to hematopoietic tissues, followed by a standard transplant preparative regimen. Biodistribution studies were performed in 23 patients using 0.5 mg/kg trace 131I-labeled BC8 antibody. The BC8 antibody was cleared rapidly from plasma with an initial disappearance half-time of 1.5 +/- 0.2 hours, presumably reflecting rapid antigen-specific binding. The mean radiation absorbed doses (cGy/mCi131I administered) were as follows: marrow, 7.1 +/- 0.8; spleen, 10.8 +/- 1.4; liver, 2.7 +/- 0.2; lungs, 2.1 +/- 0.1; kidneys, 0.7 +/- 0.1; and total body, 0.4 +/- 0.03. Patients with acute myelogenous leukemia (AML) in relapse had a higher marrow dose (11.4 cGy/mCi) than those in remission (5.2 cGy/mCi; P = .001) because of higher uptake and longer retention of radionuclide in marrow. Twenty patients were treated with a dose of 131I estimated to deliver 3.5 Gy (level 1) to 7 Gy (level 3) to liver, with marrow doses of 4 to 30 Gy and spleen doses of 7 to 60 Gy, followed by 120 mg/kg cyclophosphamide (CY) and 12 Gy total body irradiation (TBI). Nine of 13 patients with AML or refractory anemia with excess blasts (RAEB) and two of seven with acute lymphocytic leukemia (ALL) are alive disease-free at 8 to 41 months (median, 17 months) after BMT. Toxicity has not been measurably greater than that of CY/TBI alone, and the maximum tolerated dose has not been reached. This study demonstrates that with the use of 131I-BC8 substantially greater doses of radiation can be delivered to hematopoietic tissues as compared with liver, lung, or kidney, which may improve the efficacy of marrow transplantation.

Post therapy imaging in high dose I-131 radioimmunotherapy patients

The biodistribution of a trace-labeled I-131 antibody is used to predict the biodistribution of a high dose I-131 antibody for therapy. Internal radiation dose estimates derived from the trace-labeled antibody have been used to determine the I-131 doses in a phase I escalating dose therapy trial for hematologic malignancy. To confirm the hypothesis that the distribution of a trace- and high-dose labeled antibodies are similar, both trace (7-11 mCi, 259-407 MBq) and high-dose (100-800 mCi, 3700-29600 MBq) I-131 radiolabeled antibody infusion were imaged in 12 patients who were treated for leukemia or lymphoma. With specialized imaging techniques using lead attenuation sheets, clearance data from organs were obtained from serial gamma camera images. Biological clearance half times of I-131 from both trace and therapy level doses were in agreement. An exception was a patient who developed human antimouse antibody before therapy, and subsequently had rapid clearance of the therapy dose. The method was feasible, yielded reproducible results, and provided critical data for relating therapy toxicity to radiation absorbed dose estimates.

Samarium-153-EDTMP in bone metastases of hormone refractory prostate carcinoma: a phase I/II trial

Samarium-153-ethylenediaminetetramethylene phosphoric acid (EDTMP), a bone-seeking radiopharmaceutical, was given to prostate cancer patients in a dose escalation protocol for pain palliation to determine the maximally tolerated dose. Fifty-two patients with hormone refractory prostate cancer with bony metastases were treated with doses beginning at 0.5 mCi/kg (18.5 MBq/kg), escalating in 0.5-mCi (18.5 MBq) increments to 3.0 mCi/kg (111 MBq/kg). Pain response after treatment was assessed as well as hematologic and serum chemistry parameters. Pain palliation with a mean duration of 2.6 mo was present in 74% of the patients. Toxicity was exclusively hematologic at the highest dose levels. No infectious or bleeding complications occurred, with 45 of the 52 (86%) patients demonstrating complete hematologic recovery. Patients receiving higher doses had significantly greater reductions in serum prostate specific antigen and serum prostatic acid phosphatase levels. The patients receiving greater doses also showed a trend toward improved survival.

Radiolabeled-antibody therapy of B-cell lymphoma with autologous bone marrow support

BACKGROUND

Radiolabeled monoclonal antibodies recognizing B-lymphocyte surface antigens represent a potentially effective new therapy for lymphomas. We assessed the biodistribution, toxicity, and efficacy of anti-CD20 (B1 and 1F5) and anti-CD37 (MB-1) antibodies labeled with iodine-131 in 43 patients with B-cell lymphoma in relapse.

METHODS

Sequential biodistribution studies were performed with escalating doses of antibody (0.5, 2.5, and 10 mg per kilogram of body weight) trace-labeled with 5 to 10 mCi of 131I. The doses of radiation absorbed by tumors and normal organs were estimated by serial gamma-camera imaging and tumor biopsies. Patients whose tumors were estimated to receive greater doses of radiation than the liver, lungs, or kidneys (i.e., patients with a favorable biodistribution) were eligible for therapeutic infusion of 131I-labeled antibodies according to a phase 1 dose-escalation protocol.

RESULTS

Twenty-four patients had a favorable biodistribution, and 19 received therapeutic infusions of 234 to 777 mCi of 131I-labeled antibodies (58 to 1168 mg) followed by autologous marrow reinfusion, resulting in complete remission in 16, a partial response in 2, and a minor response (25 to 50 percent regression of tumor) in 1. Nine patients have remained in continuous complete remission for 3 to 53 months. Toxic effects included myelosuppression, nausea, infections, and two episodes of cardiopulmonary toxicity, and were moderate in patients treated with doses of 131I-labeled antibodies that delivered less than 27.25 Gy to normal organs.

CONCLUSIONS

High-dose radioimmunotherapy with 131I-labeled antibodies is associated with a high response rate in patients with B-cell lymphoma in whom antibody biodistribution is favorable.

Samarium-153-EDTMP biodistribution and dosimetry estimation

Fifty-two patients were treated with single doses of 153Sm-EDTMP in a Phase I escalating dose protocol for palliation of bone pain from metastatic prostate carcinoma. Samarium-153 (T1/2 46.3 hr), maximum beta-particle energies 810 keV (20%), 710 keV (30%), 640 keV (50%), gamma photon 103 keV (28%), was complexed to the tetraphosphonate chelate, EDTMP. Five groups of patients were treated at doses of 1.0, 1.5, 2.0, 2.5, and 3.0 mCi/kg to evaluate toxicity from treatment. Patients were screened prior to treatment and followed after treatment with 99mTc-MDP bone scans. Biodistribution data on this group of patients were acquired and showed rapid uptake of 153Sm-EDTMP into bone with complete clearance of nonskeletal radiotoxicity by 6-8 hr. Also included are complete sets of dosimetry estimations on an additional seven patients who received 0.5 mCi/kg 153Sm-EDTMP Ca++ as part of a multiple dose therapy trial. Estimated radiation absorbed doses to bone surfaces averaged 25,000 mrad/mCi (6686 Gy/MBq), and urinary bladder doses averaged 3600 mrad/mCi (964 Gy/MBq).

The use of radiolabeled anti-CD33 antibody to augment marrow irradiation prior to marrow transplantation for acute myelogenous leukemia

Disease recurrence remains a major limitation to the use of marrow transplantation to treat leukemia. Previous transplant studies have demonstrated that higher doses of total-body irradiation result in less disease recurrence, but more toxicity. In this study, the possibility of delivering radiotherapy specifically to marrow using a radiolabeled anti-CD33 antibody (p67) was explored. Biodistribution studies were performed in nine patients using .05-.5 mg/kg p67 trace-labeled with 131I. In most patients initial specific uptake of 131I-p67 in the marrow was seen, but the half-life of the radiolabel in the marrow space was relatively brief, ranging from 9-41 hr, presumably due to modulation of the 131I-p67-CD33 complex with subsequent digestion and release of 131I from the marrow space. In four of nine patients these biodistribution studies demonstrated that with 131I-p67 marrow and spleen would receive more radiation than any normal nonhematopoietic organ, and therefore these four patients were treated with 110-330 mCi 131I conjugated to p67 followed by a standard transplant regimen of cyclophosphamide plus 12 Gy TBI. All four patients tolerated the procedure well and three of the four are alive in remission 195-477 days posttransplant. This study demonstrates the feasibility of using a radiolabeled antimyeloid antibody as part of a marrow transplant preparative regimen and also highlights a major limitation of using conventionally labeled anti-CD33--namely, the short residence time in marrow. Strategies to overcome this limitation include the use of alternative labeling techniques or the selection of cell surface stable antigens as targets.

Skeletal nonvisualization in a bone scan secondary to intravenous etidronate therapy

Etidronate disodium (EHDP) therapy is often instituted emergently for treatment of hypercalcemia associated with malignancy, and a staging bone scan is part of the evaluation of the patient with extensive metastatic disease. In these patients in whom high dose EHDP therapy has been instituted, uptake of the bone scan agent is markedly diminished. The case presented illustrates this finding: a breast cancer patient who had received two 500-mg intravenous doses of EHDP prior to bone scan staging. No skeletal visualization was present at 3 hr after 99mTc-MDP injection. Blood-pool activity and uptake in large metastatic sites were observed.

A method for imaging therapeutic doses of iodine-131 with a clinical gamma camera

Imaging therapeutic doses of 131I-labeled monoclonal antibody would provide valuable biodistribution data for dosimetry, but gamma cameras are unable to accurately handle the corresponding high counting rate. To image patients undergoing radioimmunotherapy, we attached 1.6- to 6.4-mm-thick Pb sheets to the front face of a high-energy parallel-hole collimator. With this method, we were able to acquire planar images of up to 700 mCi of radiolabeled antibody 1 hr after infusion. Monte Carlo simulations indicated that less than 7% of the events counted in the photopeak window were due to 364-keV photons that scattered in the Pb attenuator. Measurements indicated that the Pb sheets degraded system resolution by no more than 13%. A quantitative comparison of trace and therapy biodistribution data from planar images of the same patient was made using corrections for Pb sheet attenuation and camera deadtime.

Vascular response to radiation injury in the rat lung

Changes in relative left-to-right lung blood flow ratios were followed as an index of vascular radiation injury in left-hemithorax-irradiated Sprague-Dawley rats. Single doses of 11 to 21 Gy gamma radiation resulted in a dose-dependent decrease in relative blood flow to the irradiated lung from 3 to 5 weeks after exposure during the development of pneumonitis. Blood flow returned to near normal by 5 weeks after lower doses (11-13.5 Gy). After a single dose of 15 Gy the left-to-right blood flow ratio recovered to 75% of normal at 12 weeks and leveled off. Following 18 Gy irradiation a second period of reduced flow began 16 weeks after exposure. After 21 Gy irradiation flow to the irradiated side remained low for 1 year after exposure. Rats that received a single dose of 18 Gy to the left hemithorax were also treated with one or two of the following drugs: captopril, cyproheptadine, dexamethasone, diethylcarbamazine, penicillamine, or theophylline. Dexamethasone was most effective at preventing the decrease in blood flow to the irradiated lung when treatment was continued through the pneumonitis period and dose was not tapered until 8 weeks after radiation exposure. All other drugs and drug combinations were, for the most part, virtually ineffective after the pneumonitis period. There was a relatively poor correlation with earlier vascular permeability surface area product studies. This suggests that endothelial damage, as well as damage to other cell types, contributes to the development of post-irradiation fibrosis in the lung.

Localization of radiolabeled antimyeloid antibodies in a human acute leukemia xenograft tumor model

Acute myeloid leukemia is an attractive disease to treat with radiolabeled antibodies because it is radiosensitive and antibody has ready access to the marrow cavity. In order to evaluate potentially useful radiolabeled antibodies against human acute myeloid leukemia, we have developed a nude mouse xenograft model using the human acute leukemia cell line, HEL. Mice with s.c. xenografts of HEL cells received infusions of radioiodinated anti-CD33 antibody. Examination of the biodistribution of the antibody showed that uptake in the s.c. tumor was maximal [16.9% injected dose (ID)/g at 1 h after infusion] following infusion of 1-10 micrograms of antibody and decreased following infusion of 100 micrograms (6.5% ID/g at 1 h) presumably as a result of saturation of antigen sites. The radiolabel was poorly retained in tumor (4.5-8.2% ID/g at 24 h after infusion). These results were consistent with in vitro studies demonstrating rapid internalization and catabolism of the anti-CD33 antibody. Uptake in tumor could be improved by using either a radiolabel that is retained intracellularly, 111In-DTPA (18.5% ID/g at 24 h), or by targeting a surface antigen that does not internalize upon antibody binding, CD45 (20.5% ID/g at 24 h). These results indicate that this model system will be useful in evaluating the interaction of radiolabeled antibodies with human acute myeloid leukemia cells in an in vivo setting.