Why has radiography become a thing of the past?
For a long time, it was believed that regular chest X-ray (CXR) could help detect tumors at early stages. However, a large-scale PLCO study (more than 154,000 participants) showed that the use of CXR does not lead to a reduction in mortality from lung cancer, even if the disease is detected somewhat earlier. Therefore, isolated radiography has no practical value for screening today.
Low-dose CT: the new standard
The first attempts to use volumetric CT for screening were made in Japan. Later, the ELCAP study confirmed that low-dose CT (LDCT) allows the detection of tumors at early stages when the cure rate is significantly higher.
The largest proof of LDCT efficacy was the NLST study (US National Cancer Institute), covering more than 53,000 smokers. Over three years, participants were examined annually using LDCT or CXR.
Results of NLST:
- LDCT detects cancer at earlier stages, most often adenocarcinomas.
- The rate of positive CT findings reached 39% (versus 16% for CXR).
- Main conclusion: LDCT reduces lung cancer-specific mortality by 20%.
Despite the proven efficacy, mass implementation of screening is controversial due to the psychological burden on patients: the small nodules found require prolonged (up to 2 years) follow-up to rule out a malignant process.
Technical features and data processing
Modern screening is performed on multislice computed tomography (MSCT / MDCT) scanners with a slice thickness of 1 mm (unlike older machines with 10 mm slices).
Special technologies are used to facilitate nodule detection:
- MIP (Maximum intensity projection) is a simple reconstruction technique that makes lesions more visible.
- CAD (Computer-assisted diagnosis) are programs that automatically highlight suspicious areas. They reduce physician fatigue and increase accuracy, but produce many false-positive results that the radiologist must filter out manually.
Management of detected nodules and radiation dose
It is important to understand that over 98% of detected nodules are benign and do not grow. To monitor small lesions (5–8 mm), the Fleischner Society (Fleischner guidelines) or British Thoracic Society recommendations are used.
Assessment of nodule growth using standard 2D measurements is inaccurate and poorly reproducible. The modern standard is semi-automated volumetry (semi-automated nodule volume), which calculates nodule volume with high precision.
Since benign changes are frequently found during screening, the radiation dose must be minimized. To achieve this, LDCT protocols are used, which imply:
- reducing tube current and voltage;
- increasing the beam pitch (pitch).
Briefly: answers to topical questions
What criteria (age, smoking history) determine whether a patient belongs to the risk group eligible for screening?
A patient's risk group for screening is determined by strict age limits and smoking history. The patient must simultaneously meet the following criteria:
- Age — from 55 to 80 years.
- Smoking status — current smoker with a smoking history of 30 pack-years or more, or quit smoking no more than 15 years ago.
What clinical guidelines and scales are used for managing patients with detected pulmonary nodules?
The Fleischner Society and British Thoracic Society recommendations are used to guide the management of patients with detected pulmonary nodules.
| Characteristic | Fleischner Society (Fleischner Society) | British Thoracic Society (BTS) |
|---|---|---|
| Publication year | 2017 | 2015 |
| Target population | Age 35 years and older | Age 18 years and older |
| Applicability | Incidental nodules | All pulmonary nodules |
| Measurement method | Average of diameters | Volumetry |
To assess the risk of malignancy in the British Thoracic Society guidelines, the Brock model (Brock model) is used.
What are the absolute and relative contraindications to screening LDCT?
The sources do not provide a direct division into absolute and relative contraindications, but they identify groups of patients for whom population screening is not indicated. The method is not used for the following categories:
- Absence of risk factors — individuals without proven risk factors or with a smoking intensity of less than 30 pack-years.
- Age restrictions — patients younger than 55 years or older than 80 years.
- Chronic lung diseases — presence of severe pathology such as chronic obstructive pulmonary disease, interstitial and occupational diseases, as well as chronic infections, including tuberculosis.
Class and exam questions
Can fluorography or X-ray be used for lung cancer screening?
No. The PLCO study proved that chest radiography does not reduce lung cancer mortality, so it is not used for screening.
What is the main advantage of LDCT compared to X-ray?
Low-dose CT detects tumors at earlier stages and, according to the NLST study, reduces disease-specific mortality by 20%.
Are all nodules found on CT dangerous?
No, more than 98% of pulmonary nodules detected during screening are clinically insignificant and do not increase in size.
What is the most accurate way to measure the growth of a pulmonary nodule?
The most accurate and reproducible method is computer-aided semi-automated volumetry, which calculates the volume of the lesion rather than just its linear dimensions.
What else to study on this topic
- Criteria for including patients in risk groups for screening (age, smoking history).
- Detailed analysis of nodule follow-up algorithms (Fleischner Society guidelines).
- Principles of CAD systems and methods for reducing false-positive results.
- Complications of invasive diagnostics in suspected cancer (based on NLST results).
- Psychological aspects and risks of overdiagnosis in mass screening.
Master the entire topic in the "Diagnostic Radiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete guideline on «Lung Cancer Screening» and 2,199 more pages on the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 10 video lessons on the subject
Other topics in the «Chest Radiology» section
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.