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Lung-RADS standardized reporting for low-dose computed tomography for lung cancer screening

Lung-RADS standardized reporting for low-dose computed tomography for lung cancer screening
Literature review current through: Jan 2024.
This topic last updated: Jan 05, 2024.

INTRODUCTION — Patients at high risk of developing lung cancer can potentially derive a survival benefit by undergoing low-dose computed tomography (CT) lung cancer screening (CTLS).

This topic describes the CTLS protocol, the standardized system used for reporting, and the resulting management recommendations. Patient selection for and the possible benefits and harms of CTLS and the evaluation of nodules found using chest CT performed for nonscreening purposes (ie, incidental pulmonary lesion) are discussed elsewhere. (See "Screening for lung cancer" and "Diagnostic evaluation of the incidental pulmonary nodule".)

PATIENT SELECTION AND PREPARATION FOR SCREENING

Guidelines for selection — A number of governmental agencies and medical societies have published guidelines regarding high-risk patients who are eligible for low-dose CTLS (table 1). While societies differ slightly in their published recommendations for clinicians who plan on providing CTLS services, we promote the development of an eligibility policy for CTLS based upon any one or a combination of these recommendations. Accordingly, practical guidance from the American Thoracic Society (ATS) and the American Lung Association (ALA) regarding CTLS program initiation and operation has been published [1,2]. Notably, the Centers for Medicare and Medicaid Services (CMS) have their own recommendations and criteria necessary for reimbursement [3]. Further details on society recommendations are provided separately. (See "Screening for lung cancer", section on 'Recommendations by expert groups'.)

Shared decision-making — Before undergoing CTLS, documentation (at the annual office visit or at the screening site) affirming that at least one decision aid was used by the clinician and the patient for shared decision-making is necessary [3]. The provider should discuss the potential benefits and harms of screening, potential results and likelihood of follow-up diagnostic testing, the false-positive rate of CTLS, and cumulative radiation exposure. In addition, candidates must be willing to be screened annually, undergo curative therapy if diagnosed, and not have underlying comorbid conditions that significantly limit life expectancy. Electronic health record system alerts may be used to ensure that a shared decision-making discussion is accomplished prior to CTLS.

Smoking cessation — Smoking cessation and abstinence counseling is included in the shared decision-making discussion that precedes enrollment [4,5]. Smoking cessation counseling can be addressed at multiple points including during appointment scheduling and during the CT examination visit, as well as during follow-up in the results letter and discussion. The smoking history should be documented before CTLS enrollment (eg, pack-years of cigarettes, number of years quit). Such counselling is likely effective since smoking cessation rates are higher among CTLS participants than in the general population [6,7]. An overview of smoking cessation is provided separately. (See "Overview of smoking cessation management in adults" and "Screening for lung cancer", section on 'Our approach to counseling for screening'.)

Smoking cessation rates observed among participants of the CTLS program appear to be above those seen in the general population [8,9]. One study reported higher quit rates at three months in those who received counseling via telephone following CTLS compared with those who did not receive counseling (17 versus 4 percent) [10]. The overall annualized smoking cessation observed in another CTLS population was 15 percent, compared with 5 percent in the general population [6]. Relapse rates may be 15 percent lower in those who undergo CTLS compared with the general population. Success appears to correlate with the duration of participation in the screening program and a positive CT examination result [6].

Patient preparation — Patients should be free of infectious/inflammatory symptoms for 12 weeks prior to screening. Patients usually are not required to change clothing. Discussion regarding intravenous access is not needed as contrast is not administered. Metallic objects (eg, necklace, pendant) on the chest may need to be removed. (See "Principles of computed tomography of the chest".)

LOW-DOSE COMPUTED TOMOGRAPHY LUNG CANCER SCREENING PROTOCOL

Imaging protocol — Hardware and image acquisition parameters must adhere to recommended protocols for chest CTLS [5,11,12]. Chest CT performed for other indications (eg, trauma, pneumonia) will differ and usually cannot substitute for a CTLS examination.

Patients are imaged in the supine position. Patients who cannot tolerate lying supine can be imaged in the prone or decubitus position. Patients are asked to hold their breath at end-inspiration during imaging, which is typically less than five seconds on modern CT scanners.

The following technical parameters need to be met to be an accredited site for CTLS:

Multidetector helical scanner with ≥4 detector rows

Entire chest imaging

Image thickness of ≤2.5 mm

Volume CT dose index ≤3 milligray (for "standard"-sized patients [ie, 5 feet 7 inches and 154 pounds])

Dose modulation, either manual or automatic, according to patient size

Several agencies including The American College of Radiology (ACR) and the American Association of Physicists in Medicine (AAPM) also provide guidance for other technical parameters for CTLS (eg, tube rotation time, anatomical coverage, kilovolts, pitch, milliampere-seconds, scan duration, reconstruction image-spacing and algorithm, and display field of view and windowing parameters) [11,13] or provide assistance for screening center designation [14].

Radiation dose — Radiation exposure from a single CTLS exam is, on average, about 1 millisievert (mSv). To put this into context, annual radiation exposure from natural background sources is, on average, 3.1 mSv in the United States. Worldwide it is 2.4 mSv per year, lower in some parts of the world (eg, Canada at 1.8 mSv per year), and higher in other parts. The average dose from mammography is 0.7 mSv. No ill-health effects from such low doses are likely in adults since radiation effects have not been proven to exist in patients exposed to levels below 100 mSv above background [15].

Sites accredited for CTLS must demonstrate adherence to radiation dose limits [16]. For reimbursement purposes, the Centers for Medicare and Medicaid Services (CMS) have mandated that several predefined CTLS technical parameters for each CT examination be entered into an approved national registry [5]. In addition, the ACR Lung Cancer Screening Registry reports radiation dose from individual participating institutions compared with regional and national averages [17].

In the future, an opportunity to lower CTLS dose below 1 mSv may be available with ≥64 detector row scanners and dose reduction software. However, implementation of lower dose limits awaits more universal propagation of this scanner technology.

LUNG IMAGING COMPUTED TOMOGRAPHY SCREENING REPORTING AND DATA SYSTEM (LUNG-RADS)

General principles — CTLS reporting is standardized according to the lung CT screening reporting and data system (Lung-RADS) [18]. When evaluating the CT, the radiologist reports a Lung-RADS score (LR 0 through 4), which accounts for pulmonary nodules and other findings concerning for lung cancer (eg, airway nodules, atypical cystic lesions), as well as potentially inflammatory/infectious lesions, and any significant incidental findings (eg, adrenal nodule). Each LR category is associated with an estimate of lung cancer risk. Based upon this risk, recommendations for further management of the abnormality are made. (See 'Lung-RADS (LR) categories: Assigning lung cancer risk' below and 'Significant incidental findings (S modifier)' below.)

Components of the evaluation — Lung-RADS evaluation involves several assessments, which are discussed in this section.

Pulmonary parenchymal nodules — The radiologist assesses features similar to those used to describe incidental pulmonary nodules with notable differences. Nodule consistency, size, and growth are the major factors considered in the LR score. Other nodule factors which could affect the LR score include perifissural and juxtapleural nodule location (may lower the score) and a spiculated border (may raise score). (See "Diagnostic evaluation of the incidental pulmonary nodule", section on 'Nodule features'.)

Nodule consistency – Based on their CT attenuation, nodules are generally classified as solid, part-solid, or non-solid (ground-glass). The likelihood of underlying lung cancer varies with nodule consistency, the details of which are provided separately. (See "Diagnostic evaluation of the incidental pulmonary nodule", section on 'Attenuation'.)

Size and lower limit threshold – Lung-RADS defines nodule size as the mean of the long and short axes. Solid and part-solid nodules can be considered positive on a baseline screening exam if they measure ≥6 mm; non-solid nodules are considered positive if they measure ≥3 cm. Corresponding volumetric nodule thresholds are also incorporated into Lung-RADS.

Per Lung-RADS, nodule measurements are obtained in lung windows and are reported to the nearest one decimal point (eg, 5.4 mm). However, in some practices, including ours, nodule size is reported in 1 mm integer ranges (ie, 5 to 6 mm, 12 to 13 mm). This enables the radiologist to convey the limits of the spatial resolution of the CTLS imaging and more clearly report inter-reader variability versus true nodule growth in follow-up.

In Lung-RADS, the lower limit size threshold of solid nodules ≥6 mm was chosen to minimize the false-positive rate of baseline examinations without significantly increasing the false-negative rate:

The National Lung Screening Trial (NLST) reported a mortality benefit from lung cancer screening using a maximum diameter nodule size threshold of ≥4 mm [19]. However, in the NLST, increasing the nodule size threshold to a mean diameter of ≥6 mm (ie, similar to that used in Lung-RADS) decreased the detection rate of positive nodules from 27 to 13 percent without significantly changing the overall false-negative rate.

The International Early Lung Cancer Action Program (IELCAP) defined the nodule size as the mean of the long and short axes. Using positive nodule size thresholds of 5 and 6 mm mean diameter, the rate of detecting positive nodules was 16 and 10 percent, respectively, with no observed delay in cancer diagnosis using a 6 mm threshold [20,21].

Growth – Growth is defined as an increase in nodule size >1.5 mm (mean diameter) within a 12-month period. Thus, when the nodule size is increased but does not meet the 1.5 mm growth threshold, the assigned LR score and follow-up interval recommendations for the nodule remain unchanged. For ground-glass or part-solid nodules, development of a new or enlarging solid component, even in the absence of overall nodule growth, can prompt the LR score to be upgraded.

Exceptions include solid, part-solid, or ground-glass nodules demonstrating growth over multiple screening examinations but not meeting the >1.5 mm increase in size for any 12-month interval. A slow-growing non-solid nodule may be classified as Lung-RADS 2 until the nodule meets criteria of another category, such as developing a solid component (then manage per part-solid nodule criteria). A solid or part-solid nodule demonstrating slow growth over multiple screening exams is suspicious and may be classified as Lung-RADS 4B. Another exception is when a nodule crosses a new size threshold for another Lung-RADS category, even if not meeting the definition of growth, the nodule should be reclassified based on size and managed accordingly.(See 'Lung-RADS (LR) categories: Assigning lung cancer risk' below.)

The definition of growth for an atypical cystic lung lesion is discussed below. (See 'Atypical cystic lesions' below.)

Airway nodules — Airway nodules identified during screening are also included on Lung-RADS scoring. This includes any rounded, tubular, or soft-tissue nodules in the trachea or endobronchial tree, regardless of benign or malignant features. Segmental and proximal airway lesions and lesions with a soft tissue component are more likely to be malignant while subsegmental and/or multiple tubular endobronchial abnormalities favor a benign etiology. Absence of soft tissue components, low attenuation (<20 Hounsfield units), and presence of air within airway abnormalities are considered benign features suggestive of secretions. As benign airway findings often resolve on follow-up imaging, persistence of airway nodules in proximal or segmental airways should prompt additional evaluation (including PET/CT if there is a large solid component or referral to bronchoscopy).

Airway nodules are part of Lung-RADS scoring because in one large lung cancer screening study, 22 percent of cancers missed at initial screening were central endobronchial lesions [22,23].

Growth of an airway nodule is not defined, but persistence of an airway nodule in proximal or segmental airway at three months (even in absence of growth) upgrades the lesion to category 4B and prompts further diagnostic evaluation per Lung-RADS.

Atypical cystic lesions — Occasionally, malignancy is associated with a cystic lesion within the pulmonary parenchyma. Atypical cystic lesions were not initially included but are reported in Lung-RADS 2022 and include the following:

Thick-walled (≥2 mm) cyst

Multilocular cyst

Growing thick-walled or multilocular cyst

Growing cystic component in a previously stable thick-walled cyst

Multilocular cyst with increased loculation or density

Cyst with adjacent nodules

Cavitary nodules, especially those where the soft tissue component of the cavity wall is greater than the cavitary/cystic component (ie, most of the cyst is composed of the wall and has minimal cavitation)

If a cyst is associated with a nodule, Lung-RADS addresses the most concerning feature.

Growth of a cystic lesion is defined as a >1.5 mm increase in cyst size (mean diameter), wall thickness, and/or size of the cystic component (mean diameter) occurring within a 12-month interval.

Unilocular thin-walled cysts and fluid-containing cysts are not classified by Lung-RADS since they are unlikely to have malignant potential (eg, fluid containing cysts, which often indicate infection). Additionally, multiple cysts indicating an alternative diagnosis are not classified by Lung-RADS (eg, lymphangioleiomyomatosis, Birt-Hogg-Dubé, pulmonary Langerhans cell histiocytosis). If, however, there is a particular lesion that looks different or more concerning, that lesion could be singled out and evaluated by Lung-RADS. Further details regarding the diagnostic approach to cystic lung lesions are provided in a separate topic. (See "Diagnostic approach to the adult with cystic lung disease".)

Potentially infectious or inflammatory lesions — Lung lesions that are potentially infectious or inflammatory are also evaluated in Lung-RADS. What comprises a potentially infectious or inflammatory lesion is poorly defined. Nonetheless, we consider lesions with any one of the following in this category:

Pulmonary lesions appearing in a short interval (eg, segmental or lobar consolidation, multiple new nodules [more than six in number], large solid nodules [≥8 mm])

New nodules in certain clinical contexts (eg, immunocompromised patient)

Tree-in-bud nodules/abnormalities

Some of these findings may be indeterminate for infection/inflammation or obscure underlying lung parenchyma constituting an incomplete exam. (See 'LR-0 "incomplete"' below.)

Incidental lesion unrelated to lung cancer screening — Incidental findings require an 'S' modifier in Lung-RADS, but Lung-RADS does not specify what constitutes an 'S' modifier nor does it dictate the associated management. This designation is largely left to the discretion of the interpreting radiologist. Generally, we define a significant incidental finding as any unexpected finding that is either new or unknown (eg, ascending aortic aneurysm) and requires some form of further clinical or imaging evaluation before the next scheduled CTLS examination. Findings that are already known, treated, or in the process of clinical evaluation do not require an 'S' modifier. The CT may have a single or multiple significant incidental findings, each of which would be associated with a specific recommendation for further management. Further details regarding examples and how this is reported are found below. (See 'Significant incidental findings (S modifier)' below.)

LUNG-RADS (LR) CATEGORIES: ASSIGNING LUNG CANCER RISK — An LR score between 0 and 4 is assigned based on the estimated risk of developing lung cancer within the following year (table 2) [18]. If there are multiple abnormalities, the most suspicious one determines the overall LR score. Each score is associated with a management recommendation. Lung-RADS defines LR-1 and LR-2 as "negative" and LR-3 and LR-4 as "positive" CTLS examinations. The vast majority of examinations are LR-1 and LR-2 (85 percent) while the remainder are LR-3 and LR-4. With the new addition in 2022 of LR-0, future data will determine how category assignments are distributed.

Importantly, LR scoring is not appropriate for reporting chest CT examinations performed in patients not undergoing screening since the LR system assumes that repeat annual screening examinations will be performed. For example, an examination categorized as negative within Lung-RADS may contain indolent or very early forms of lung cancer that are unlikely to become clinically active until the next screening examination while the same findings outside the Lung-RADS system would require a specific recommendation for subsequent follow-up. (See "Diagnostic evaluation of the incidental pulmonary nodule", section on 'Management'.)

The timing of follow-up imaging dictated by the Lung-RADS category is from the date of the examination being interpreted and not from the baseline examination.

LR scores are periodically revised; the most recent version is Lung-RADS 2022 (table 2) [18].

LR-0 "incomplete" — An LR-0 score is assigned when the acquired images are technically inadequate or image interpretation is awaiting comparison with prior chest CT examinations. It is also used in situations where the lung parenchyma and evaluation may be obscured by infectious/inflammatory findings. A risk for lung cancer cannot be assigned, and thus, a recommendation for further management from a potential lung cancer perspective cannot be made.

Risk of lung cancer – Patients with nodules in this category cannot be assessed for the risk of malignancy.

Prevalence – This category is rarely used (population prevalence approximately 1 percent), but it is important for program personnel to review these cases to identify and correct potential errors in patient instruction and/or scan acquisition. Since this is an updated category since Lung-RADS 1.1, the prevalence may change.

Examples – Examples include examinations with breathing/motion artifact, insufficient beam strength, incomplete lung coverage, or findings that suggest inflammatory/infectious etiology. (See 'Potentially infectious or inflammatory lesions' above.)

Management – In these patients, the recommendation is based upon the reason for an incomplete examination. Examples include the need for comparison with a prior chest CT (eg, patients with history of longstanding upper lobe scarring), repeat CTLS examination (eg, patient with motion artifact, incomplete lung coverage), or follow up CT within one to three months (eg, potentially inflammatory/infectious lesions). Also rarely, some findings do not require follow up (eg, tree-in-bud abnormalities). At follow-up a new LR may be assigned, and assessment is based upon the most suspicious CT finding.

LR-1 "negative" — CT examinations with no nodules or those that appear definitively benign are assigned an LR-1 category.

Risk of lung cancer – Patients with nodules in this category have a <1 percent probability of developing clinically active cancer in the next year [18].

Prevalence – The population prevalence of LR-1 nodules is approximately 39 percent. However, in regions where granulomatous infections are endemic, these rates are likely higher.

Examples – Examples include examinations with no nodules or definitively benign-appearing nodules. Examples of benign nodules on imaging include those containing fat and specific patterns of calcifications (ie, complete, central, concentric, or popcorn). For example, a fully calcified healed granuloma or definitively benign hamartoma would fall into this category. (See "Diagnostic evaluation of the incidental pulmonary nodule", section on 'Benign etiologies'.)

Management – Patients should return for CTLS in 12 months. If there is a change in the category due to development of a new nodule 6 mm or larger, or a solid component, or growth of the nodule per the criteria, further follow-up for that category is advised.

LR-2 "benign-appearing or behaving" — LR-2 lesions are those that have a low likelihood of being lung cancer.

Risk of lung cancer – Patients with nodules in this category also have a <1 percent probability of developing clinically active cancer in the next year [18].

Prevalence – The estimated population prevalence is approximately 45 percent.

Examples – On baseline imaging, this category includes the following:

Solid or part-solid nodules:

-<6 mm solid or part-solid nodules

-New <4 mm solid nodule (ie, "micronodules")

Ground-glass nodules:

-New or growing <30 mm ground-glass nodules

-Stable or slowly growing ≥30 mm ground-glass nodules

Category 3 or 4 nodules:

-Category 3 nodule that is unchanged at six months

-Category 3 or 4A nodule that resolves on follow-up

-Category 4B nodule proven to be benign after diagnostic investigations

Perifissural, juxtapleural, subsegmental airway nodules:

-Perifissural and juxtapleural nodules <10 mm that have solid smooth margins and are oval, lentiform, or triangular in shape

Subsegmental airway nodule

Management – Patients should return for CTLS in 12 months. If there is a change in the category due to development of a new nodule 6 mm or larger, or a solid component, or growth of the nodule per the criteria, further follow-up for that category is advised.

LR-3 "probably benign" — LR-3 lesions also have a low likelihood of being lung cancer but higher than LR-2 lesions.

Risk of lung cancer – Patients with nodules in this category have a <5 percent probability of clinically active cancer in the next year [23].

Prevalence – The estimated population prevalence of this category is approximately 9 percent.

Examples – Examples include the following:

On baseline CT examination, this category includes:

-6 to <8 mm solid nodules

-≥6 mm part-solid nodules with solid components measuring <6 mm

-≥30 mm non-solid nodules

On follow-up CT examination, this category includes:

-New solid nodules measuring 4 to <6 mm

-New part-solid nodules <6 mm total diameter

Management – Patients should return for CTLS in six months (image 1). If at six-month follow-up the LR-3 findings are stable or resolve, the examination becomes LR-2 and the next examination is performed at 12 months after this follow-up examination. If there is a change in the category due to development of a new nodule, or a solid component, or growth of the nodule per the criteria, further follow-up for that category is advised.

LR-4 "suspicious" — Generally speaking, this category includes large or growing nodules and solidifying part- and non-solid nodules. It also includes other findings concerning for malignancy, such as unilateral pleural thickening, asymmetric interlobular septal thickening, lymphadenopathy in the lung cancer nodal stations, nodule spiculation, and necrotic appearance or abnormal enhancement of normal size lymph nodes in the lung cancer stations. Depending on the nature of the nodule, the LR-4 category is recorded as one of three subcategories (4A, 4B, or 4X), which are discussed below. (See 'LR-4A "suspicious"' below and 'LR-4B "very suspicious"' below and 'LR-4X' below.)

Many CTLS programs advise that all LR-4 cases be presented for multidisciplinary review that includes pulmonary, thoracic surgery, oncology, radiology, radiation oncology, and pathology experts [24]. This enables the care team to individualize the management approach and account for patient-related variables including patient performance status and care team preferences regarding the role of positron emission tomography (PET)/CT, biopsy, surgery, and surveillance. (See "Selection of modality for diagnosis and staging of patients with suspected non-small cell lung cancer", section on 'Role of multidisciplinary teams' and "Diagnostic evaluation of the incidental pulmonary nodule", section on 'Individualizing the approach'.)

LR-4A "suspicious" — LR-4A lesions are at high risk for being malignant.

Risk of lung cancer – Patients with nodules in this category have, at minimum, a 5 to 16 percent probability of clinically active cancer in the next year (image 1 and image 2). In our clinical practice, we found a frequency of malignancy among category 4A nodules to be 15.5 percent [23].

Prevalence – Patients in this category have an estimated population prevalence of 4 percent.

Examples – Examples include the following:

On baseline examination, this category includes:

-8 to <15 mm solid nodules

-≥6 mm part-solid nodules with solid components measuring 6 to <8 mm

-Segmental or proximal airway nodules

-Thick-walled or multilocular cyst

On follow-up, this category includes the following:

-New solid nodules measuring 6 to <8 mm

-Growing solid nodules measuring <8 mm

-≥6 mm part-solid nodules with new or growing solid components measuring <4 mm

-New segmental or proximal airway nodules

-Thin- or thick-walled cyst that becomes multilocular

Management – Patients should return for CTLS in three months. Nodules that are stable or decreased at follow-up are downgraded to the next lower Lung-RADS category ("step-down management") whereas those that have grown usually require clinical investigation.

However, in practice, in patients considered at highest risk, such as those with a nodule containing a solid component ≥8 mm, a PET/CT scan is often performed at short-term follow-up rather than waiting for a repeat CT scan.

Choosing among these options is at the discretion of the subspecialist(s). Factors that may influence this decision are discussed separately. (See "Diagnostic evaluation of the incidental pulmonary nodule", section on 'Individualizing the approach'.)

LR-4B "very suspicious" — LR-4B lesions have a higher risk for being malignant than LR-4A.

Risk of lung cancer – Patients with nodules in this category have, at minimum, a >15 percent probability of clinically active cancer in the next year. However, in our experience, the risk may be higher (eg, 36 to 37 percent) [23,25].

Prevalence – Patients in this category have an estimated population prevalence of 2 percent.

Examples – Examples include the following:

On baseline examination, this category includes:

-≥15 mm solid nodules

-Part-solid nodules with a solid component measuring >8 mm

On follow-up, this category includes:

-New or growing solid nodules measuring ≥8 mm

-Part-solid nodules with new or growing solid components measuring ≥4 mm

-Slow-growing solid or part-solid nodule that demonstrates growth over multiple screening examinations

-Persistent or growing proximal or segmental airway nodule

-Thick-walled atypical cyst with growing wall thickness/nodularity

-Growing multilocular atypical cyst

-Multilocular atypical cyst with increased loculation or new/increased opacity (nodular, ground-glass, or consolidation)

Management – Formal subspecialty consultation is appropriate for these patients to determine the next steps including the decision to proceed with PET/CT, biopsy, or surgery. Choice among these options is tailored to the likelihood of malignancy and patient's comorbidities. This investigation is discussed separately. (See "Diagnostic evaluation of the incidental pulmonary nodule", section on 'Individualizing the approach' and "Overview of the initial evaluation, diagnosis, and staging of patients with suspected lung cancer".)

LR-4X — CTLS images with nodules that fall into category 3 or 4 by the above criteria but contain additional imaging findings that increase suspicion for lung cancer (such as spiculation, lymphadenopathy, metastatic disease, etc) are assigned an LR-4X score. This category provides the reading radiologist with flexibility to upgrade a CT examination if features not specified in an LR category increase the suspicion for lung cancer even if they do not explicitly meet the LR-4A or LR-4B criteria.

Risk of lung cancer – This designation is typically for nodules that have highest risk of malignancy based on imaging. Based on our review, 77 percent of LR-4X nodules were malignant [23].

Prevalence – The estimated population prevalence is <1 percent.

Examples – Examples are category 3 or 4 lesions that have a pleural effusion or pleural nodularity, interlobular septal thickening, lymphadenopathy, spiculated nodules, frank metastatic disease, and a ground-glass nodule that doubles in size within 12 months. Nodules in this category have an appearance or growth pattern highly suspicious for clinically significant malignancy.

Management – Formal subspecialty consultation is appropriate for these patients to determine the next steps, including the decision to proceed with short interval follow-up CTLS, PET/CT, biopsy, or surgery. This evaluation is discussed in detail separately. (See "Diagnostic evaluation of the incidental pulmonary nodule", section on 'Individualizing the approach' and "Overview of the initial evaluation, diagnosis, and staging of patients with suspected lung cancer".)

Significant incidental findings (S modifier) — An 'S' modifier is used for CT examinations with significant incidental findings unrelated to lung cancer screening, a phenomenon that is not uncommon. The letter 'S' is added to the LR category (0 to 4), creating 14 possible overall LR examination assessment results (0, 0S, 1, 1S, 2, 2S, 3, 3S, 4A, 4AS, 4B, 4BS, 4X, 4XS). Incidental findings that are known, under evaluation, or treated do not require the continued use of an exam 'S' modifier (eg, coronary atherosclerosis in a patient with stent, bronchiectasis, old fibrosis). However, any evidence of a concerning change in a known significant or potentially significant finding that is unexpected warrants renewed use of the 'S' modifier.

Examples are lesions in the thyroid or adrenal gland, liver, or kidney. An extrapulmonary malignancy is detected incidentally in up to 0.5 percent of patients over five years of CTLS [25-27]. Kidney cancer, lymphoma, and thyroid cancer are the most common cancers detected incidentally.

The rate of "S-positive" findings reported by different CTLS programs varies since a consensus on what constitutes a significant incidental finding is lacking.

When applicable, management of findings leading to an 'S' modifier is encouraged to adhere to available American College of Radiology (ACR) Incidental Findings management recommendations.

ALTERNATIVE STANDARDIZED REPORTING SYSTEMS — There are other CTLS reporting systems, in addition to Lung-RADS. The oldest and most widely used is the International Early Lung Cancer Action Program (IELCAP) protocol [28]. Other primarily research-based systems, such as Lu-RADS, have also been used in clinical trials [29]. However, in the United States, Centers for Medicare and Medicaid Services (CMS) have approved only one national registry for lung cancer screening and that registry mandates the use of Lung-RADS for reporting [17].

DIAGNOSTIC PERFORMANCE — In randomized multicenter trials, a mortality benefit with low-dose CTLS has been demonstrated for older current smokers and former smokers. The National Lung Screening Trial (NLST) is the most well-known [30]. This study and others that demonstrate benefit are discussed separately. (See "Screening for lung cancer".)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Screening for lung cancer".)

SUMMARY AND RECOMMENDATIONS

Patient selection and preparation for lung cancer screening – Guidelines regarding high-risk patients who are eligible for low-dose CT lung cancer screening (CTLS) are available (table 1). Clinicians should develop an eligibility policy for CTLS based upon any one or a combination of these recommendations, bearing in mind that the Centers for Medicare and Medicaid Services (CMS) have their own criteria necessary for reimbursement. (See 'Guidelines for selection' above and 'Patient selection and preparation for screening' above and "Screening for lung cancer".)

Documentation should affirm that smoking cessation counseling, which included the use of at least one decision-aid, occurred before enrollment. All qualified candidates should be free of infectious/inflammatory symptoms for 12 weeks prior to screening, and discussion regarding intravenous contrast is not necessary. Patients should preferably be able to lie in the supine position and hold their breath at end-inspiration for up to five seconds. (See 'Smoking cessation' above and 'Patient preparation' above.)

Imaging protocol and radiation dose – Hardware and image acquisition parameters must adhere to recommended protocols for CTLS. Accredited sites should adhere to the following technical parameters: a multidetector helical scanner with ≥4 detector rows; entire chest imaging with single breath hold full inspiration; image thickness of ≤2.5 mm; volume CT dose index ≤3 milligray; and dose modulation according to patient size. Radiation exposure from a single CTLS examination is about 1 millisievert (mSv). To put this into context, annual radiation exposure from natural background sources is, on average, 3.1 mSv in the United States, and average dose from mammography is 0.7 mSv. (See 'Low-dose computed tomography lung cancer screening protocol' above.)

Lung-RADS assessment – CTLS reporting is standardized according to the lung CT screening reporting and data system (Lung-RADS).

When evaluating the CT, the radiologist assesses findings concerning for lung cancer, as well as potentially inflammatory/infectious lesions and any significant incidental findings (eg, adrenal nodule). (See 'Lung imaging computed tomography screening reporting and data system (Lung-RADS)' above and 'General principles' above.)

When assessing risk for lung cancer, nodule consistency, size, and growth as well as the presence and appearance of airway nodules (eg, location and shape) and atypical cystic lesions (eg, growth, wall thickness, loculations, adjacent nodules, cavitation) are evaluated. (See 'Components of the evaluation' above.)

Lung-RADS categories – Based on this assessment, a Lung-RADS (LR) score between 0 and 4 is assigned. (See 'Lung-RADS (LR) categories: Assigning lung cancer risk' above.)

Each category indicates the estimated risk of developing clinically active lung cancer within one year. If there are multiple findings, the most suspicious one determines the overall LR score. Each score is associated with a management recommendation. Lung-RADS defines LR-1 and LR-2 as "negative" and LR-3 and LR-4 as "positive" CTLS examinations. LR-0 is an incomplete examination that cannot be assessed. Details of what constitutes a specific LR score and the associated recommendation are listed on the table (table 2) and discussed in the following links:

-(See 'LR-0 "incomplete"' above.)

-(See 'LR-1 "negative"' above.)

-(See 'LR-2 "benign-appearing or behaving"' above.)

-(See 'LR-3 "probably benign"' above.)

-(See 'LR-4 "suspicious"' above.)

The radiologist also reports on incidental findings found on the CT ('S' modifier). A significant incidental finding is any unexpected finding unrelated to lung cancer screening that is either new or unknown and requires some form of further clinical or imaging evaluation before the next scheduled CTLS examination (eg, adrenal, liver, kidney, thyroid lesion). The letter 'S' is added to the LR score, creating 14 possible overall LR examination assessment results (0, 0S, 1, 1S, 2, 2S, 3, 3S, 4A, 4AS, 4B, 4BS, 4X, 4XS). The CT may have multiple significant incidental findings, each of which would be associated with a specific recommendation for further management. Incidental findings that are known, under evaluation, or treated do not require the continued use of an exam 'S' modifier. (See 'Significant incidental findings (S modifier)' above.)

Diagnostic performance – A lung cancer-specific mortality benefit with CTLS has been demonstrated in older current and former smokers in randomized multicenter trials, among which the National Lung Screening Trial (NLST) is the most well-known. These data are discussed separately. (See 'Diagnostic performance' above and "Screening for lung cancer".)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Brady J McKee, MD (deceased), who contributed to earlier versions of this topic review.

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Topic 121013 Version 12.0

References

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