Abstract 1136: Tumor uptake and biodistribution of 89Zirconium-labeled ipilimumab in patients with metastatic melanoma during ipilimumab treatment

Introduction

Ipilimumab, a monoclonal antibody targeting CTLA-4, is approved for the treatment of metastatic melanoma and significantly improves overall survival. Because of the high costs and the potential serious toxicity of ipilimumab, it is of great importance to identify biomarkers that correlate with clinical activity and that can be used to select patients who will benefit from CTLA-4 blockade therapy.

We hypothesize that patients who do not respond to treatment with ipilimumab have lower drug levels in tumor tissues as compared to patients with a good response to therapy. In addition, we hypothesize that immune related adverse events (irAEs) are associated with high drug levels in the affected tissue. As irAEs usually occur approximately 6-8 weeks after the first injection of ipilimumab, we hypothesize that the drug levels in potentially affected tissues will increase at the second injection.

Experimental procedures

To visualize in vivo localization of ipilimumab in patients diagnosed with metastatic melanoma, 37 MBq, 10 mg 89Zr-labeled ipilimumab was injected within 2 hours after their first ipilimumab dose (3 mg/kg). Whole body PET/CT scans were obtained at 2h, 72h and 144h post injection and this procedure was repeated three weeks later at the second ipilimumab cycle. Biodistribution and tumor uptake were assessed visually by a nuclear physician. Focal uptake in tumor lesions exceeding local background was determined in volumes of interest (VOI) and SUVpeak values were obtained. Biodistribution was quantified by defining vital organs (i.e. lungs, kidneys, spleen, liver) and calculating mean %ID/kg. Blood was drawn for dosimetry and immunophenotyping at several time points during the trial. Presented here are initial results of the first three patients, up to 29 patients are planned to be included.

Results

Biodistribution of 89Zr-labeled ipilimumab showed a pattern distinctive for 89Zr-labeled antibodies with uptake in liver and spleen, as well as prolonged circulating antibody in the bloodstream corresponding to the pharmacokinetics of ipilimumab. Visual evaluation confirmed uptake of 89Zr-labeled ipilimumab in 5/12 evaluable tumor lesions, visible at both first and second injection of ipilimumab. Tumor uptake was comparable for 72h and 144h post injection with a mean of 6.9 %ID/kg (range 3.3-10.1) and a SUVpeak of 4.4 (range 2.3-8.9). There were no significant differences in tumor uptake between first and second dose of ipilimumab (mean 7.31 and 6.54 %ID/kg respectively).

Conclusions

Preliminary data of this ongoing study showed that the tracer is able to visualize and quantify uptake of ipilimumab in tumors. Correlations between tumor uptake and response to treatment will be presented. Furthermore, special interest will be given to uptake in lymphoid organs and locations for irAEs.

Citation Format: Iris H. Miedema, Gerben J. Zwezerijnen, Guus A. van Dongen, Daniëlle J. Vugts, Marc C. Huisman, Otto S. Hoekstra, Tanja D. de Gruijl, Hendrik M. Verheul, Catharina W. Menke, Alfons J. van den Eertwegh. Tumor uptake and biodistribution of 89Zirconium-labeled ipilimumab in patients with metastatic melanoma during ipilimumab treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1136.

An automatic delineation method for bone marrow absorbed dose estimation in (89)Zr PET/CT studies

Background

The study aims to develop and validate an automatic delineation method for estimating red bone marrow (RM) activity concentration and absorbed dose in ⁸⁹Zr positron emission tomography/computed tomography (PET/CT) studies. Five patients with advanced colorectal cancer received 37.1 ± 0.9 MBq [⁸⁹Zr] cetuximab within 2 h after administration of a therapeutic dose of 500 mg m⁻² unlabelled cetuximab. Per patient, five PET/CT scans were acquired on a Gemini TF-64 PET/CT scanner at 1, 24, 48, 96 and 144 h post injection. Low dose CT data were used to manually generate volumes of interest (VOI) in the lumbar vertebrae (LV). In addition, LV VOI were generated automatically using an active contour method in a low dose CT. RM activity was then determined by mapping the low dose CT-derived RM VOI onto the corresponding PET scans. Finally, these activities were used to derive residence times and, subsequently, the self and total RM absorbed doses using OLINDA/EXM 1.1.

Results

High correlations (r² > 0.85) between manual and automated VOI methods were obtained for both RM activity concentrations and total absorbed doses. On average, the automatic method provided values that were lower than 5 % compared to the manual method.

Conclusions

An automated and efficient VOI method, based on an active contour approach, was developed, enabling accurate estimates of RM activity concentrations and total absorbed doses.

Electronic supplementary material

The online version of this article (doi:10.1186/s40658-016-0149-0) contains supplementary material, which is available to authorized users.

Validation of simplified dosimetry approaches in ⁸⁹Zr-PET/CT: the use of manual versus semi-automatic delineation methods to estimate organ absorbed doses

PURPOSE

Increasing interest in immuno-positron emission tomography (PET) studies requires development of dosimetry methods which will provide accurate estimations of organ absorbed doses. The purpose of this study is to develop and validate simplified dosimetry approaches for (89)Zirconium-PET (Zr-PET)/computed tomography (CT) studies.

METHODS

Five patients with advanced colorectal cancer received 37.1 ± 0.9 MBq (89)Zr-cetuximab within 2 h after administration of a therapeutic dose of 500 mg m(-2) cetuximab. PET/CT scans were obtained 1, 24, 48, 94, and 144 h post injection. Volumes of interest (VOIs) were manually delineated in lungs, liver, spleen, and kidneys for all scans, providing a reference VOI set. Simplified manual VOIs were drawn independently on CT scans using larger voxel sizes. The transformation of VOIs based on rigid and/or nonrigid registrations of the first CT scan (CT1) onto all successive CT scans was also investigated. The transformation matrix obtained from each registration was applied to the manual VOIs of CT₁ to obtain VOIs for the successive scans. Dice similarity coefficient (DSC) and Hausdorff distance were used to assess the performance of the registrations. Organ total activity, organ absorbed dose, and effective dose were calculated for all methods.

RESULTS

Semi-automatic delineation based on nonrigid registration showed excellent agreement for lungs and liver (DSC: 0.90 ± 0.04; 0.81 ± 0.06) and good agreement for spleen and kidneys (DSC: 0.71 ± 0.07; 0.66 ± 0.08). Hausdorff distance ranged from 13 to 16 mm depending on the organ. Simplified manual delineation methods, in liver and lungs, performed similarly to semi-automatic delineation methods. For kidneys and spleen, however, poorer accuracy in total activity and absorbed dose was observed, as the voxel size increased. Organ absorbed dose and total activity based on nonrigid registration were within 10%. The effective dose was within ±3% for all VOI delineation methods.

CONCLUSIONS

A fast, semi-automatic, and accurate delineation method based on nonrigid registration was developed for determination of organ absorbed and effective dose in (89)Zr-PET/CT studies which may also be applied to other long-lived radionuclide PET/CT studies.

PET/CT-derived whole-body and bone marrow dosimetry of 89Zr-cetuximab

PET/CT imaging allows for image-based estimates of organ and red marrow (RM) residence times. The aim of this study was to derive PET/CT-based radiation dosimetry for (89)Zr-cetuximab, with special emphasis on determining RM-absorbed dose.

METHODS

Seven patients with colorectal cancer received 36.9 ± 0.8 MBq of (89)Zr-cetuximab within 2 h after administration of a therapeutic dose of 500 mg·m(-2) of cetuximab. Whole-body PET/CT scans and blood samples were obtained at 1, 24, 48, 94, and 144 h after injection. RM activity concentrations were calculated from manual delineation of the lumbar vertebrae and blood samples, assuming a fixed RM-to-plasma activity concentration ratio (RMPR) of 0.19. The cumulated activity was calculated as the area under the curve of the organ time-activity data (liver, lungs, kidneys, spleen, and RM), assuming physical decay after the last scan. The residence time for each organ was derived by dividing the cumulated activity with the total injected activity. The residence time in the remainder of the body was calculated as the maximum possible residence time minus the sum of residence time of source organs, assuming no excretion during the time course of the scans. The (self and total) RM- and organ-absorbed doses and effective whole-body radiation dose were obtained using dose conversion factors from OLINDA/EXM 1.1. Several simplified 3-time-point dosimetry approaches were also evaluated.

RESULTS

The first approach yielded self and total RM doses of 0.17 ± 0.04 and 0.51 ± 0.06 mGy·MBq(-1), respectively. The second approach deviated by -21% in self-dose and -6% in total dose. RMPR increased over time in 5 of 7 patients. The highest (89)Zr-absorbed dose was observed in the liver with 2.60 ± 0.78 mGy·MBq(-1), followed by the kidneys, spleen, and lungs, whereas the effective whole-body dose was 0.61 ± 0.09 mSv·MBq(-1). The simplified 3-time-point (1, 48, and 144 h) dosimetry approach deviated by at most 4% in both organ-absorbed doses and effective dose.

CONCLUSION

Although the total RM dose estimates obtained with the 2 approaches differed only by at most 6%, the image-based approach is preferred because it accounts for nonconstant RMPR. The number of successive scans can be reduced to 3 without affecting effective dose estimates.