Low-dose computed tomography (LDCT) is a digital X-ray imaging technique that generates detailed images or scans of internal body areas. By capturing multiple images from various angles, it can present both two-dimensional (2D) and three-dimensional (3D) representations of any chest pathology. LDCT images are more detailed than a conventional X-ray.
LDCT is a painless and non-invasive procedure that doesn’t involve contrast material injections or oral substances.
The LDCT scan typically lasts less than a minute. Throughout the process, the patient remains motionless on the CT scan bed. Depending on the equipment, the bed either moves slowly through the center of the scanner or remains stationary while the scanner rotates around the patient. Buzzing noises may be heard during the scan. At times, the technician may instruct the patient to hold their breath to prevent image blurring.
While low-dose radiation CT (LDCT) can provide detailed information on factors like lesion size, shape, or location, it cannot definitively diagnose whether a lesion is cancerous.
It’s good to know:
Despite the advantages of lung cancer screening, such as decreased mortality and improved quality of life, there are also drawbacks and risks to consider:
- Suspicious findings may require further investigation with additional scans or biopsies, the majority of which turn out to be non-cancerous.
- Very small or concealed cancerous tumors within the chest may go undetected.
- Patients are exposed to a small amount of radiation during the procedure. Although this radiation dose is lower than that of a standard CT scan, repeated LDCTs may result in higher cumulative radiation exposure, potentially increasing the risk of future cancers.
- Some detected tumors may be slow-growing and may not require immediate treatment.
- Patients may incur out-of-pocket expenses that are not covered by insurance.
- Waiting for test results can cause stress and anxiety.
- Screening can only be performed at facilities equipped to conduct low-dose CT scans, potentially requiring patients to travel for the test.
Additionally, it’s important to note that LDCT may reveal abnormal findings in tissues and organs outside the lungs (incidental non-pulmonary findings), which should be evaluated by the treating physician.
What is shared decision-making? Why is it important for lung cancer screening?
In an ideal scenario, the decision to undergo screening is jointly made by the patient and their primary care physician or chest physician. The physician is more familiar with the patient’s medical history and potential risk factors and can guide them to the appropriate screening facility. (Certain diagnostic centers may necessitate a medical referral in advance, while others conduct a risk assessment to determine if the patient’s history and risk factors warrant the screening without a referral.) Typically, a personal consultation with the primary care physician or chest physician is necessary prior to screening. During this consultation, the doctor will gather specific details about the patient’s current and past smoking habits, and together, they will discuss the advantages and disadvantages of CT lung scans and smoking cessation counseling. This consultation is referred to as a shared decision-making session. The information collected and documented in the medical records will determine eligibility for low-dose radiation CT (LDCT) screening.
Pulmonary Nodules
Lesions identified through low-dose computed tomography (LDCT) are known as pulmonary nodules. Nodules represent tissue growths that appear as white shadows with a round or oval shape. Lung nodules are very common, with the majority being non-cancerous. Remarkably, only about 4% of nodules detected during screening are cancerous.
Characteristics of a nodule include:
Size: Nodules are typically measured in millimeters (mm). Many nodules are very small, approximately the size of a pea (around 5 mm).
Shape: Lung nodules may have a smooth or uneven surface marked by spicules (spikes or points) or lobules (multiple rounded nodules clustered together). Spiculated or lobulated nodules are more likely to be cancerous.
Density: Lung nodules are categorized based on how solid or indistinct-how dense they appear on LDCT imaging. They are classified as solid, non-solid, or part- solid:
- Solid nodules, resembling the density of muscles, are the densest and commonly detected.
- Non-solid nodules appear less distinct and are sometimes referred to as “ground-glass” nodules. They are considered less likely to be cancerous.
- Part- solid nodules display both solid and non-solid characteristics, appearing fuzzy on imaging. They are considered more likely to be cancerous.
What causes the development of lung nodules?
Lung nodules can occur due to various reasons besides lung cancer, with the majority being non-cancerous. Causes of lung nodules, apart from lung cancer, include:
Infections: Bacterial and fungal infections can cause lung nodules, known as granulomas, which are small cellular clusters formed post-infection due to inflammation. Examples of bacterial infections include mycobacterium (such as Mycobacterium tuberculosis or Mycobacterium avium-intracellulare). Examples of fungal infections include histoplasmosis and coccidioidomycosis.
Non-infectious causes: Conditions like sarcoidosis, which leads to granulomas in the lungs and other body parts, and rheumatoid arthritis, can also trigger the formation of nodules in the lungs.
Neoplasms: Neoplasms refer to any abnormal growths, which can be either cancerous or non-cancerous. The most prevalent type of benign neoplasm is an hamartoma.
What happens when a lung nodule is detected during lung cancer screening?
Low-dose computed tomography (LDCT) can accurately detect lung nodules, which are small, round or oval tissue growths within the lung appearing as white shadows on examination. However, LDCT alone cannot determine whether the nodule is cancerous or benign. As previously mentioned, the majority of nodules detected by LDCT are non-cancerous.
The initial screening is known as baseline screening. Subsequent LDCT scans, known as follow-up tests, are compared to the baseline scan to assess any changes that may indicate lung cancer. The patient’s medical history, nodule characteristics, and growth rate determine the need for further evaluation.
Based on the detection of lung nodules during baseline screening, the NCCN® recommends the following:
If no nodules are detected, the next LDCT should be conducted at 12 months, with additional follow-up scans every subsequent year. The frequency of follow-up tests is determined by the physician.
If nodules are found:
Size: Larger nodules require more frequent monitoring. Nodules with a diameter equal to or less than 5 mm are less concerning.
Density: The density of a nodule refers to its compactness, determined by how effectively LDCT X-rays penetrate it. Compact and partially compact nodules raise greater concern for lung cancer.
Location: Nodules in the upper lung lobes are more likely to be cancerous.
Growth rate: Rapidly growing nodules are more likely to be cancerous. Nodule growth rate is assessed by comparing sizes on follow-up scans.
Medical history: The healthcare team assesses lung cancer risk factors, including age and family history.
If a nodule exhibits concerning characteristics during screening or follow-up LDCT scans, a biopsy or surgical removal may be performed to confirm malignancy. Further tests may be required to determine cancer stage. Treatment for early-stage patients typically involves surgery or stereotactic body radiotherapy (SBRT), while advanced-stage patients undergo treatment after comprehensive biomarker screening and individualized targeted treatment planning.
The American College of Radiology has introduced a rating system known as Lung CT Screening Reporting & Data System® (Lung-RADS®) to standardize the reporting of CT scan findings. This aims to mitigate confusion in the interpretation of lung cancer screening CT scans and enhance the quality of follow-up scans and care.
A higher Lung-RADS® score indicates a greater likelihood of the nodule being cancerous and necessitating further evaluation. However, not all LDCT results are currently reported using the Lung-RADS® system.
Recent advancements in lung cancer screening
Improvements in imaging techniques, notably low-dose computed tomography (LDCT), have enhanced the prospects of detecting lung cancer in its early stages. Scientists are actively exploring alternative methods for early lung cancer detection. Ongoing research focuses on developing more sensitive tests capable of detecting indicators of lung cancer in sputum or blood, potentially identifying the disease even before it becomes visible on CT scans. Research is also trying to determine if biomarker testing can identify individuals at higher risk of lung cancer.
