Page 37 - ARNM-2-3

Advances in Radiotherapy
& Nuclear Medicine Molecular imaging of lung cancer

and 7 NSCLC patients to measure tumor uptake and glucose uptake, as well as false-negative findings for small
whole-body biodistribution before treatment with a PD-1 lesions (<5 mm). To achieve more accurate diagnoses, the
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antibody. They reported no significant difference in tracer integration of two imaging modalities, such as PET/CT or
uptake between patients with melanoma and those with PET/MRI, is often necessary. 75
NSCLC, and a mean SUV max of 6.5 was observed. The
study demonstrated that Zr-labeled pembrolizumab PET 4. MRI
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imaging is a safe, non-invasive modality for visualizing Compared to CT and PET, MRI-based early lung cancer
PD-1 biodistribution. Another study by Niemeijer et al. detection is free of ionizing radiation, allowing a wide
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compared PET imaging with the PD-1 targeting drug variety of longitudinal scans and avoiding radiation-
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89 Zr-Nivolumab and PD-L1 targeting drug 18 F-BMS- induced cancer. 77,78 MRI offers several key advantages,
986192 in 13 patients with advanced NSCLC. Both tracers including high spatial and temporal resolution, which
provided sufficient tumor-to-background contrast for allows for detailed visualization of both anatomy
effective tumor visualization. The study found that patients (structure) and function (activity) within the body. In
with tumor biopsies showing aggregates of PD-1 had addition, the wide field of view of MRI and its multi-planar
higher Zr-Nivolumab uptake, indicating a correlation acquisition permit image capture from various angles,
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between PD-L1 expression and Zr-Nivolumab uptake. 23 providing a comprehensive understanding of the scanned
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area. However, the application of MRI to the lungs has
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3.5. Targeting somatostatin receptor (SSTR)
its limitations. 76,80,81 First, the lung has a limited signal
SSTRs are G protein-coupled receptors that modulate source due to its low tissue density. Second, the interface
apoptosis and regulate cell proliferation. These receptors between air and lung tissue results in a short T2*, making
are expressed in normal cells and various malignant cells, it difficult for traditional spin echo pulse sequences to
including neuroendocrine tumors (NET), SCLC, and capture the rapidly decaying magnetic resonance (MR)
NSCLC. The most widely used PET tracer for imaging signal in the lung. Third, respiratory and cardiac motion
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SSTRs is Ga-DOTATATE, which has shown a high requires breath-holding or gating during an MRI scan to
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affinity for SSTR type 2. This high affinity results in superior obtain motion-free images. To address these limitations,
imaging quality, shorter image acquisition times, and lower continuous efforts have been made to optimize and apply
radiation doses. In a 2023 study, Hu et al. compared the different MRI pulse sequences for lung MRI. Beyond
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efficacy of Ga-DOTATATE and F-FDG PET/CT in improving MRI pulse sequences, new contrast-enhanced
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diagnosing and staging well-differentiated and poorly molecular MRI has shown strong translational applications
differentiated NET. They reported that F-FDG PET/CT in early lung cancer detection.
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accurately detected 23 out of 27 patients confirmed by
pathology to have NET, with a sensitivity of 85.2% and a 4.1. Conventional MRI
specificity of 37.5%. In contrast, Ga- DOTATATE correctly Conventional MRI pulse sequences, such as diffusion-
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detected all 27 patients, demonstrating a sensitivity of 100% weighted (DW) MRI, along with T1-weighted (T1W) and
and a specificity of 93.8%, which was higher than that of T2-weighted (T2W) MRI sequences, have been studied
18 F-FDG PET/CT. Another study by Walker et al. assessed to detect lung cancer nodules. As mentioned above,
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the imaging efficiency of Ga DOTATATE PET/CT in lung parenchyma appears dark in MR images due to low
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detecting indeterminate pulmonary nodules and lung proton density and short T2*. Therefore, solid tumor
cancer. Their results showed that 68 Ga- DOTATATE masses appear bright in both T1W and T2W images
was more specific (94%) and less sensitive (73%) than due to higher proton density, while tumors also appear
18 F-FDG (81% specificity and 93% sensitivity) in detecting bright in DW images due to the faster diffusivity of water
indeterminate pulmonary nodules and lung cancer. In molecules within the tissue. Conventional lung MRI has
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addition, uptake in normal lung tissue was low and similar been reported in clinical settings to detect malignant lung
between Ga-DOTATATE and F-FDG. 72 tumors. Qi et al. found that DW MRI outperformed CT
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in distinguishing between lung cancer and post obstructive
3.6. Limitations of PET scans lobar collapse, and the combination of T2W and DW
The primary limitation of PET imaging is its substantially MRI further improved the diagnosis of early-stage lung
lower resolution and limited anatomical detail. This cancer. Satoh et al. reported that DW MRI could be used
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results in poor localization of lesions and inadequate to differentiate between malignant and benign tumors.
demarcation of lesion borders. In addition, while F-FDG- Coolen et al. reported that DW MRI is a promising tool
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PET is highly beneficial, it has been associated with false- for detecting malignant pleural disease, outperforming
positive findings due to inflammatory cells exhibiting high FDG-PET/CT. Hu et al. reported that T1W and T2W
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Volume 2 Issue 3 (2024) 5 doi: 10.36922/arnm.4173