Lung cancer imaging. Future Developments

CONTENTS:

2.8 Developments in Lung Cancer Imaging
2.8.1 High Resolution CT (HRCT)
2.8.2 Computer Aided Detection (CAD) and CADx
2.8.3 Positron Emission Tomography (PET)
2.8.4 Integrated PET and CT
2.9 Radiographic Staging of Lung Cancer
2.9.1 CT Scan of the Chest
2.9.2 Radiologic Lung Cancer ‘Stages’ (A, B, C, D)
2.9.3 PET in Staging Lung Cancer
2.9.2 Whole Body PET

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2.8 Developments in Lung Cancer Imaging

For second-line imaging in screened patients who have lung abnormalities detected by LDCT, there are a number of developments in lung cancer imaging.

2.8.1 High-Resolution CT (HRCT)

In symptomatic, non-screened, patients, the chest X-ray gives a large amount of information; this is in relation to radiation dose, its cost, availability, and ease of performance. But there are limitations to the PA chest X-ray as it is normally in between 10% to 15 % of symptomatic patients with proven infiltrative lung disease.

High Resolution CT (HRCT) has a sensitivity of 95 % and a specificity approaching 100 % and can often provide more information than either chest radiography or a conventional CT scan. It can be used to detect or evaluate metastatic tumors and solitary pulmonary nodules.

What’s the difference between sensitivity and specificity?

‘Sensitivity’ means how many people who actually have the disease test positive.

So with the HRCT scan, out of 100 people with the disease 95 will test as positive.

Yes, and ‘specificity’ means how many people without the disease will test as negative.

2.8.2 Computer Aided Detection (CAD) and CADx

Software systems for computer image analysis have been developed to assist the radiologist in the interpretation of CT scans.

Several CAD systems have now received approval from the U.S. Food and Drug Administration (FDA).

However at present it is still not clear whether these CAD systems really do improve cancer detection in lung screening programs.

But CAD software can be used to help radiologists to report the increasing number of diagnostic CT images that need interpretation. As CT advances, hundreds of thin-slice images may now be produced for a chest CT study.

CAD software tools for chest CT are used in LDCT lung cancer screening. But the use of CAD in chest CT has been focused primarily either on the detection of pulmonary nodules or for the characterization of lung nodules as potentially benign or malignant.

Additional features can be included in CAD tools to detect malignant nodules, the so-called CADx software tools.

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2.8.3 Positron Emission Tomography (PET)

Positron emission tomography (PET) scanning is used prior to surgery and when looking for metastatic lung cancer. For minimally invasive needle techniques used to stage lung tumors involving the mediastinum and mediastinal lymph nodes, PET has become accepted as a first choice lung cancer imaging technique.

2.8.4 Integrated PET and CT

lung cancer imaging The addition of PET-CT to the evaluation of diagnosed lung cancer may have significant clinical impact.

Studies have shown some marked improvement in the staging systems of lung cancer, using PET-CT. In a study by Subedi and colleagues in 2009, clinical patient management was found to be more appropriately targeted, following PET-CT. These researchers also found that PET permitted reduction in the number of thoracotomies performed for non-resectable disease, with a reduction in the morbidity rate and reduction in cost associated with unnecessary interventions.

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2.9 Lung Cancer Imaging and Staging

Any abnormal imaging findings should be confirmed by tissue biopsy, by whatever method is available, to ensure accurate lung cancer staging. Evidence suggests that more complete and accurate staging improves patient outcomes.

The clinical staging of patients with confirmed or suspected non-small-cell lung cancer (NSCLC) includes the following:

Imaging of the chest with contrast-enhanced CT.
Imaging of the upper abdomen – including the liver and adrenal glands, usually by extension of the chest CT through the upper abdomen.
Imaging of sites of potential lung cancer metastasis when symptoms or focal findings are present.
CT and (in some cases) PET to provide a non-invasive assessment of tumor size (T), mediastinal node enlargement (N), and intra- or extra-thoracic metastases (M)

Features that may suggest mediastinal lymph node metastases include:

Lymph node size > 1 cm by short-axis diameter on transverse CT scan and / or,
Increased uptake of FDG on PET imaging (e.g., FDG uptake greater than that of mediastinal blood pool).

The low sensitivity and specificity of CT (55 % and 81 %) and PET (80 % and 88 %) may miss occult cancer and result in ‘false-negatives.’

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2.9.1 CT Scan of the Chest

All patients with suspected or biopsy-confirmed NSCLC should undergo CT scan of the chest; preferably, this should be a contrast-enhanced CT.

Intravenous (IV) contrast enhancement may distinguish between direct mediastinal invasion of the primary lung cancer and a metastasis to lymph nodes. Imaging of the liver and adrenal glands should also be done.

CT scans assess the anatomic location and size of the tumor (T), nodal involvement (N), and metastatic disease involving the pleura, liver, and adrenal glands (M).

2.9.2 Radiologic Lung Cancer ‘Stages’ (A, B, C, D)

In 2013, the ACR suggested four major radiographic stages to be used to facilitate further diagnostic work-up and staging.

These four groups include patients with the following findings on CT scan:

A: Patients with bulky tumor encircling or invading mediastinal structures such that isolated lymph nodes cannot be distinguished from a primary tumor. These patients are not candidates for surgical treatment.

B: Patients with discrete lymph node involvement such that an isolated lymph node can be distinguished from the primary tumor.

C: Patients with central tumor and elevated risk of nodal disease despite normal-sized nodes (i.e., high-risk N2/3 disease).

D: Patients with low-risk of N2/3 involvement or distant metastatic disease (i.e., peripheral T1 tumors).
The allocation of patients to these categories may help to guide the clinician in the selection of a targeted site for tissue biopsy.

A limitation of CT is its low accuracy in the identification of mediastinal metastases. In 2013, in a systematic review by Silvestri and colleagues, of 43 studies, the accuracy of CT as a mediastinal staging tool was assessed in 7,368 patients with suspected NSCLC. These patients had a positive CT scan, defined as lymph nodes measuring > 1 cm; the prevalence of mediastinal metastasis was 30 %. CT imaging predicted mediastinal lymph node metastases with a high degree of sensitivity and specificity.

Due to its low sensitivity and specificity, CT scanning is not a reliable imaging technique for staging lung cancer in the mediastinum. Tissue sampling and histopathology diagnosis are required to confirm regional mediastinal lymph node metastases

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2.9.3 PET in Staging Lung Cancer

In the 2013 ACCP lung cancer staging guidelines, Silvestri and colleagues have reported that PET scanning has now assumed a key role in staging of lung cancer prior to surgery and when evaluating the presence of metastatic disease.

2.9.4 Whole Body PET

There is no consensus on the use of whole-body PET as a routine staging method. Whole-body PET is more accurate than CT in detecting small tumor foci its use has not been proven to improve patient survival. There is conflicting evidence on whether PET can reduce the risks of unnecessary thoracotomy.

The use of PET imaging as a staging option should be considered in the context of the risk of missing occult disease, local expertise, and patient preferences.

When staging the mediastinum, there are risks associated with PET.

‘False-positives‘ can occur with benign FDG-avid lesions such as infections, inflammation, and granulomatous disease. ‘False-negatives‘ can occur when there are microscopic foci of cancer metastasis, and in non-enlarged lymph nodes (< 10 mm).

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References:

Subedi N, Scarsbrook A, Darby M, Korde K, Mc Shane P, Muers MF. (2009). The clinical impact of integrated FDG PET-CT on management decisions in patients with lung cancer. Lung Cancer. 64(3), 301-7. (Retrieved 30^th Jan 2015): http://www.ncbi.nlm.nih.gov/pubmed?term=19004519

Silvestri GA, Gonzalez AV, Jantz MA, et al. (2013). Methods for staging non-small cell lung cancer: Diagnosis and management of lung cancer. 3rd ed: American College of Chest Physicians evidence-based clinical practice guidelines. Chest 143(5 Suppl), e211S. (Retrieved 29th Jan 2015): https://www.ncbi.nlm.nih.gov/pubmed/23649440

More references for this section are on this page.

Patient Information:

Cancer Research UK Pet Scan. (Retrieved 26^th March 2015): http://www.cancerresearchuk.org/about-cancer/cancers-in-general/tests/pet-scan

NHS Choices Lung cancer – Diagnosis . (Retrieved 9^th April 2015): http://www.nhs.uk/conditions/cancer-of-the-lung/Pages/Diagnosis.aspx

More patient information for this section is on this page.

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