B.A.W. Hoeben

PET of Hypoxia with 89Zr-Labeled cG250-F(ab′)2 in Head and Neck Tumors

Hypoxic tumor cells are resistant to radiotherapy and various chemotherapeutic agents. The pretherapeutic assessment of intratumoral hypoxia may allow selection of patients for intensified treatment regimens. Carbonic anhydrase IX (CAIX) is an endogenous hypoxia-related protein involved in pH regulation and is upregulated in many tumor types. Radionuclide imaging using a monoclonal antibody against CAIX, such as cG250, may allow noninvasive PET of hypoxia in these tumor types. The aims of this study were to investigate whether 89Zr-labeled cG250-F(ab′)2 allowed visualization of tumor hypoxia using small-animal PET and whether the tracer showed spatial correlation to the microscopic distribution of CAIX-expressing cells in a human head and neck xenograft tumor model. Methods: Athymic mice with subcutaneous human head and neck carcinoma xenografts (SCCNij3) were imaged with small-animal PET after injection of 89Zr-cG250-F(ab′)2. PET images were parameterized in terms of standardized uptake values (SUVs). After injection with the nitroimidazole hypoxia marker pimonidazole and the perfusion marker Hoechst 33342, the animals were sacrificed, tumors excised, and CAIX- and pimonidazole-marked hypoxia and blood perfusion were analyzed immunohistochemically. 89Zr-cG250-F(ab′)2 tumor uptake was analyzed by ex vivo activity counting and by autoradiography of tumor sections. Results: As early as 4 h after administration, accumulation of 89Zr-cG250-F(ab′)2 in the tumor had occurred and tumors were clearly visualized by PET, with reduced uptake by 24 h after injection. Pixel-by-pixel analysis showed a significant positive spatial correlation between CAIX expression and 89Zr-cG250-F(ab′)2 localization (r = 0.57–0.74; P < 0.0001). Also, significant correlations were found between pimonidazole staining intensity and 89Zr-cG250-F(ab′)2 activity concentration, although less strong (r = 0.46–0.68; P < 0.0001). Tumor maximum SUV correlated significantly with tumor uptake determined ex vivo (r = 0.93; P = 0.0067), as did fractions of CAIX and pimonidazole in tumor sections (r = 0.75; P = 0.03 and r = 0.78; P = 0.02, respectively). Conclusion: 89Zr-labeled cG250-F(ab′)2 small-animal PET showed rapid accumulation in a head and neck xenograft tumor model with good correlation to CAIX expression on a microscopic level.

18F-FLT PET During Radiotherapy or Chemoradiotherapy in Head and Neck Squamous Cell Carcinoma Is an Early Predictor of Outcome

This prospective study used sequential PET with the proliferation tracer 3′-deoxy-3′-18F-fluorothymidine (18F-FLT) to monitor the early response to treatment of head and neck cancer and evaluated the association between PET parameters and clinical outcome. Methods: Forty-eight patients with head and neck cancer underwent 18F-FLT PET/CT before and during the second and fourth weeks of radiotherapy or chemoradiotherapy. Mean maximum standardized uptake values for the hottest voxel in the tumor and its 8 surrounding voxels in 1 transversal slice (SUVmax(9)) of the PET scans were calculated, as well as PET-segmented gross tumor volumes using visual delineation (GTVVIS) and operator-independent methods based on signal-to-background ratio (GTVSBR) and 50% isocontour of the maximum signal intensity (GTV50%). PET parameters were evaluated for correlations with outcome. Results: 18F-FLT uptake decreased significantly between consecutive scans. An SUVmax(9) decline ≥ 45% and a GTVVIS decrease ≥ median during the first 2 treatment weeks were associated with better 3-y disease-free survival (88% vs. 63%, P = 0.035, and 91% vs. 65%, P = 0.037, respectively). A GTVVIS decrease ≥ median in the fourth treatment week was also associated with better 3-y locoregional control (100% vs. 68%, P = 0.021). These correlations were most prominent in the subset of patients treated with chemoradiotherapy. Because of low 18F-FLT uptake levels during treatment, GTVSBR and GTV50% were unsuccessful in segmenting primary tumor volume. Conclusion: In head and neck cancer, a change in 18F-FLT uptake early during radiotherapy or chemoradiotherapy is a strong indicator for long-term outcome. 18F-FLT PET may thus aid in personalized patient management by steering treatment modifications during an early phase of therapy.

Molecular PET imaging for biology-guided adaptive radiotherapy of head and neck cancer

Abstract Integration of molecular imaging PET techniques into therapy selection strategies and radiation treatment planning for head and neck squamous cell carcinoma (HNSCC) can serve several purposes. First, pre-treatment assessments can steer decisions about radiotherapy modifications or combinations with other modalities. Second, biology-based objective functions can be introduced to the radiation treatment planning process by co-registration of molecular imaging with planning computed tomography (CT) scans. Thus, customized heterogeneous dose distributions can be generated with escalated doses to tumor areas where radiotherapy resistance mechanisms are most prevalent. Third, monitoring of temporal and spatial variations in these radiotherapy resistance mechanisms early during the course of treatment can discriminate responders from non-responders. With such information available shortly after the start of treatment, modifications can be implemented or the radiation treatment plan can be adapted tailing the biological response pattern. Currently, these strategies are in various phases of clinical testing, mostly in single-center studies. Further validation in multicenter set-up is needed. Ultimately, this should result in availability for routine clinical practice requiring stable production and accessibility of tracers, reproducibility and standardization of imaging and analysis methods, as well as general availability of knowledge and expertise. Small studies employing adaptive radiotherapy based on functional dynamics and early response mechanisms demonstrate promising results. In this context, we focus this review on the widely used PET tracer 18F-FDG and PET tracers depicting hypoxia and proliferation; two well-known radiation resistance mechanisms.

Radiolabeled cetuximab: Dose optimization for epidermal growth factor receptor imaging in a head‐and‐neck squamous cell carcinoma model

Noninvasive imaging of the epidermal growth factor receptor (EGFR) in head‐and‐neck squamous cell carcinoma could be of value to select patients for EGFR‐targeted therapy. We assessed dose optimization of 111Indium‐DTPA‐cetuximab (111In‐cetuximab) for EGFR imaging in a head‐and‐neck squamous cell carcinoma xenograft model. 111In‐cetuximab slowly internalized into FaDu cells in vitro, amounting to 1.0 × 104 molecules cetuximab per cell after 24 hr (15.8% of added activity). In nude mice with subcutaneous FaDu xenograft tumors, a protein dose escalation study with 111In‐cetuximab showed highest specific accumulation in tumors at protein doses between 1 and 30 μg per mouse (mean tumor uptake 33.1 ± 3.1%ID/g, 3 days postinjection (p.i.)). The biodistribution of 111In‐cetuximab and 125I‐cetuximab was determined at 1, 3 and 7 days p.i. at optimal protein dose. Tumor uptake was favorable for 111In‐cetuximab compared to 125I‐cetuximab. With pixel‐by‐pixel analysis, good correlations were found between intratumoral distribution of 111In‐cetuximab as determined by autoradiography and EGFR expression in the same tumor sections as determined immunohistochemically (mean r = 0.74 ± 0.14; all correlations p < 0.0001). Micro Single Photon Emission Computed Tomography (MicroSPECT) scans clearly visualized FaDu tumors from 1 day p.i. onward and tumor‐to‐background contrast increased until 7 days p.i. (tumor‐to‐liver ratios 0.58 ± 0.24, 3.42 ± 0.66, 8.99 ± 4.66 and 16.33 ± 11.56, at day 0, day 1, day 3 and day 7 p.i., respectively). Our study suggests that, at optimal cetuximab imaging dose, 111In‐cetuximab can be used for visualization of EGFR expression in head‐and‐neck squamous cell carcinoma using SPECT.

Imaging of Epidermal Growth Factor Receptor Expression in Head and Neck Cancer with SPECT/CT and 111In-Labeled Cetuximab-F(ab′)2

Combined treatment of advanced head and neck squamous cell carcinomas (HNSCC) with radiotherapy and the epidermal growth factor receptor (EGFR) inhibitor cetuximab improves clinical outcome in comparison to radiotherapy alone but is effective only in a few cases. To select those patients most likely to benefit from EGFR inhibition, it can be advantageous to quantify the tumor EGFR status before and possibly during therapy. The aim of this study was to develop and characterize the 111In-cetuximab-F(ab′)2 tracer to image EGFR targeting in vivo. Methods: The affinity and internalization kinetics of 111In-cetuximab-F(ab′)2 were determined in vitro. The optimal protein-fragment dose for imaging was determined in nude mice with a subcutaneous head and neck carcinoma model (FaDu). Mice with FaDu tumors were imaged using ultra-high-resolution SPECT with 111In-cetuximab-F(ab′)2 or 111In-cetuximab IgG at 4, 24, 48, and 168 h after injection. Tumor tracer uptake was determined on micro-SPECT and autoradiography images of tumor sections. Immunohistochemical staining was used to analyze EGFR expression in the tumor. Results: In vitro, more than 50% of 111In-cetuximab-F(ab′)2 was internalized into FaDu cells within 24 h. The half maximal inhibitory concentration (IC50) of 111In-cetuximab-F(ab′)2 and 111In-cetuximab was similar: 0.42 ± 0.16 nM versus 0.28 ± 0.14 nM, respectively. The protein dose–escalation study showed that the highest uptake of 111In-cetuximab-F(ab′)2 in tumors was obtained at doses of 10 μg/mouse or less (13.5 ± 5.2 percentage injected dose per gram [%ID/g]). Tumor uptake of 111In-cetuximab was significantly higher (26.9 ± 3.3 %ID/g, P < 0.01). However, because of rapid blood clearance, tumor-to-blood ratios at 24 h after injection were significantly higher for 111In-cetuximab-F(ab′)2 (31.4 ± 3.8 vs. 1.7 ± 0.2, respectively; P < 0.001). The intratumoral distribution of 111In-cetuximab-F(ab′)2 correlated well with the immunohistochemical distribution of EGFR (r = 0.64 ± 0.06, P < 0.0001). micro-SPECT images of 111In-cetuximab-F(ab′)2 clearly showed preferential uptake in the tumor from 4 h onward, with superior tumor-to-background contrast at 24 h, compared with 111In-cetuximab (107.0 ± 17.0 vs. 69.7 ± 3.9, respectively; P < 0.05). Conclusion: 111In-cetuximab-F(ab′)2 displays higher tumor-to-blood ratios early after injection than 111In-cetuximab in an HNSCC model, making it more suitable for EGFR visualization and potentially for selecting patients for treatment with EGFR inhibitors.

Systematic analysis of 18F-FDG PET and metabolism, proliferation and hypoxia markers for classification of head and neck tumors

BackgroundQuantification of molecular cell processes is important for prognostication and treatment individualization of head and neck cancer (HNC). However, individual tumor comparison can show discord in upregulation similarities when analyzing multiple biological mechanisms. Elaborate tumor characterization, integrating multiple pathways reflecting intrinsic and microenvironmental properties, may be beneficial to group most uniform tumors for treatment modification schemes. The goal of this study was to systematically analyze if immunohistochemical (IHC) assessment of molecular markers, involved in treatment resistance, and 18F-FDG PET parameters could accurately distinguish separate HNC tumors.MethodsSeveral imaging parameters and texture features for 18F-FDG small-animal PET and immunohistochemical markers related to metabolism, hypoxia, proliferation and tumor blood perfusion were assessed within groups of BALB/c nu/nu mice xenografted with 14 human HNC models. Classification methods were used to predict tumor line based on sets of parameters.ResultsWe found that 18F-FDG PET could not differentiate between the tumor lines. On the contrary, combined IHC parameters could accurately allocate individual tumors to the correct model. From 9 analyzed IHC parameters, a cluster of 6 random parameters already classified 70.3% correctly. Combining all PET/IHC characteristics resulted in the highest tumor line classification accuracy (81.0%; cross validation 82.0%), which was just 2.2% higher (p = 5.2×10-32) than the performance of the IHC parameter/feature based model.ConclusionsWith a select set of IHC markers representing cellular processes of metabolism, proliferation, hypoxia and perfusion, one can reliably distinguish between HNC tumor lines. Addition of 18F-FDG PET improves classification accuracy of IHC to a significant yet minor degree. These results may form a basis for development of tumor characterization models for treatment allocation purposes.

18F-FLT PET changes during radiotherapy combined with cetuximab in head and neck squamous cell carcinoma patients.

AIM Early treatment response of head and neck cancer to radiotherapy concomitant with cetuximab was monitored by repetitive PET imaging with the proliferation tracer 18F-FLT. PATIENTS, METHODS Five head and neck cancer patients, treated with radiotherapy and concomitant cetuximab following cetuximab induction, received four 18F-FLT PET-CT scans before and during treatment. Changes in SUVpeak, SUVmean and CT- and PET-segmented gross tumour volumes were evaluated, as were correlations with immunohistochemical staining for Epidermal Growth Factor Receptor (EGFR) and Ki-67 (proliferation marker) in pre-treatment tumour biopsies. RESULTS 18F-FLT PET measured tumor responses to the induction dose of cetuximab varied from 43% SUVpeak decrease to 47% increase. After start of radiotherapy 18F-FLT PET parameters decreased significantly in all patients. No associations were found between PET parameters and EGFR or Ki-67 expression levels. CONCLUSION Proliferation of head and neck carcinomas shows a varying response to cetuximab induction, but consistently decreases after addition of radiotherapy.

Risk of benign meningioma after childhood cancer in the DCOG-LATER cohort: contributions of radiation dose, exposed cranial volume, and age

BACKGROUND Pediatric cranial radiotherapy (CrRT) markedly increases risk of meningiomas. We studied meningioma risk factors with emphasis on independent and joint effects of CrRT dose, exposed cranial volume, exposure age, and chemotherapy. METHODS The Dutch Cancer Oncology Group-Long-Term Effects after Childhood Cancer (DCOG-LATER) cohort includes 5-year childhood cancer survivors (CCSs) whose cancers were diagnosed in 1963-2001. Histologically confirmed benign meningiomas were identified from the population-based Dutch Pathology Registry (PALGA; 1990-2015). We calculated cumulative meningioma incidence and used multivariable Cox regression and linear excess relative risk (ERR) modeling. RESULTS Among 5843 CCSs (median follow-up: 23.3 y, range: 5.0-52.2 y), 97 developed a benign meningioma, including 80 after full- and 14 after partial-volume CrRT. Compared with CrRT doses of 1-19 Gy, no CrRT was associated with a low meningioma risk (hazard ratio [HR] = 0.04, 95% CI: 0.01-0.15), while increased risks were observed for CrRT doses of 20-39 Gy (HR = 1.66, 95% CI: 0.83-3.33) and 40+ Gy (HR = 2.81, 95% CI: 1.30-6.08). CCSs whose cancers were diagnosed before age 5 versus 10-17 years showed significantly increased risks (HR = 2.38, 95% CI: 1.39-4.07). In this dose-adjusted model, volume was not significantly associated with increased risk (HR full vs partial = 1.66, 95% CI: 0.86-3.22). Overall, the ERR/Gy was 0.30 (95% CI: 0.03-unknown). Dose effects did not vary significantly according to exposure age or CrRT volume. Cumulative incidence after any CrRT was 12.4% (95% CI: 9.8%-15.2%) 40 years after primary cancer diagnosis. Among chemotherapy agents (including methotrexate and cisplatin), only carboplatin (HR = 3.55, 95% CI: 1.62-7.78) appeared associated with meningioma risk. However, we saw no carboplatin dose-response and all 9 exposed cases had high-dose CrRT. CONCLUSION After CrRT 1 in 8 survivors developed late meningioma by age 40 years, associated with radiation dose and exposure age, relevant for future treatment protocols and awareness among survivors and physicians.

PD-0444 18F-FLT PET; AN EARLY PREDICTOR OF OUTCOME AFTER (CHEMO)RADIOTHERAPY IN HEAD AND NECK CANCER

Conclusions: IMRT gives the opportunity to deliver highly conformal irradiation but also implies a potential risk to miss a part of the target. In this study, almost half of all LRF appeared in the CTV HD volume. When exploring margin extension of the CTV-T HD volume it was possible to include 11% more PO’s by adding 5 mm extra margin. This does not implicate that increasing HD volume alone would reduce failure rate. The question of increasing volume and/or dose and the consequences for target and normal tissue will be further analyzed in a planning study.