Page 35 - ARNM-2-3

Advances in Radiotherapy
& Nuclear Medicine Molecular imaging of lung cancer

recent studies suggest that LDCT reduces the mortality in a CT scan is only achievable for motionless subjects,
rate in high-risk lung cancer patients by 20%, the cost- which may not be applicable for live imaging; the effect of
effectiveness and risk of overdiagnosis might be as high motion artifacts may impair imaging quality. Balancing
35
as 25%. Even the most effectively designed CT screening scan speed, dose, and diagnostic accuracy is crucial in
39
programs will capture only a small percentage of all lung developing an effective method for the application of CT.
cancers, given that only individuals at the highest risk Awareness of the radiation risks has led to the development
15
are eligible for screening. Brodersen et al. reported an of various dose reduction methods up to 1 mSv. 48
average of 49% overdiagnosis of lung cancer using LDCT,
corresponding to an absolute risk increase of 20 cancers 3. Positron emission tomography (PET)
per 1000 people screened with this method. There is a need PET is a non-invasive imaging modality that utilizes
for biomarkers to aid in selecting appropriate candidates radiotracers for the diagnosis and staging of cancer.
49
for LDCT screening and in identifying which nodules PET has been shown to be more accurate than CT in
detected by LDCT are likely malignant. differentiating benign from malignant lesions as small as
Several biomarkers have been proposed as independent 1 cm and can better identify regional or distant metastases
tools for diagnosing lung cancer. In 2022, Pastorino et al. compared to conventional imaging modalities. 50,51 PET is
reported the implementation of a combination of LDCT particularly advantageous in lung cancer diagnosis due
and a blood biomarker panel for screening, which targets to its superior ability to detect functional abnormalities
screening intervals based on initial risk prediction; this by acquiring metabolic images of the entire body. 52-54
provides a basis for the adoption of personalized screening Furthermore, PET exhibits higher accuracy than
and prevention programs. 40 conventional imaging in assessing therapeutic response,
as it can identify functional abnormalities before they
Deep learning techniques have been intensively manifest morphologically on conventional imaging. It is
researched to aid in interpreting data from CT scans for also effective in detecting viable tumor cells in instances
lung cancer detection. This method utilizes vast amounts where other imaging modalities are constrained by
of data to identify connections and patterns that may be fibrosis. Consequently, PET combined with CT (PET/CT)
55
too complex for traditional machine-learning techniques or PET/magnetic resonance imaging (PET/MRI) is often
to interpret. Deep learning methods have been applied to used for staging, follow-up, and treatment evaluation in
segment the images into anatomical components, allowing different types of malignancies. 56
for the automatic identification of lesions, nodules, and
tumors. This method is valuable because it can adapt a wide 3.1. Imaging with glucose metabolic biomarker
range of data with varying resolutions, noise levels, and 18 F-fluoro-2-deoxy-D-glucose ( F-FDG) is a glucose
18
contrast, providing real-time data processing to improve analog and the most commonly used PET radiotracer for
diagnostic accuracy and consistency, thereby reducing the lung cancer detection. The mechanism of F-FDG relies
18
likelihood of false positives and false negatives. 41-44 on the differential glucose metabolism between benign
and malignant cells. Malignant cells exhibit a higher rate
2.2. Limitations of CT scans
of glycolysis compared to benign cells, attributed to their
CT delivers radiation doses ranging from 0.22 to 0.76 Gy increased expression of glucose transporters. 50
per scan. While these doses are significantly lower than 18
45
those used for lung cancer treatment, it is important to Similar to glucose, F-FDG is taken up by malignant
18
acknowledge the potential impact of this radiation on cells and phosphorylated by hexokinase to F-FDG-6-
18
tumor growth, particularly when performing repeated phosphate. F-FDG-6-phosphate becomes sequestered in
imaging. 46,47 Furthermore, the cumulative effect of repeated malignant cells because it is not a substrate for the next
step in the glycolytic pathway. The overexpression of
51
CT scans on the immune system must be considered when glucose transporters, upregulation of hexokinase, and
developing pharmacological studies that span significant downregulation of phosphatase activity in malignant
periods. 47
cells facilitate the accumulation of F-FDG, enabling
18
The duration of exposure and the scanning material differentiation between malignant tissue and normal lung
directly influence the true resolution; when the exposure tissue. F-FDG has been reported to have a sensitivity
18
time is reduced to lower the radiation dose, a significant between 94% and 96%, a specificity between 78% and 86%,
decrease in the signal-to-noise ratio and resolution is and an accuracy between 90% and 94% in differentiating
observed. Inherent motion artifacts caused by respiration benign from malignant lung nodules. 57,58 As a result, FDG-
and internal organ movement impair the achievement of PET is commonly used for the diagnosis and staging of
the highest feasible resolution. The maximum resolution lung cancer.

Volume 2 Issue 3 (2024) 3 doi: 10.36922/arnm.4173