Whole lung CT recommended for preoperative risk assessment of lung cancer patients

Whole lung computed tomography (CT) should be used to help assess the pulmonary function of patients with lung cancer prior to having a surgical lobectomy, chest surgeons from Japan recommend in the July 2018 Journal of Thoracic Disease. By obtaining the volume of the diseased and normal lung using CT data, thoracic specialists may be able to make better functional risk assessments, especially for patients who cannot undergo spirometry.

A CT scan may help assess the pulmonary function of patients with lung cancer prior to having a surgical lobectomy. By obtaining the volume of the diseased and normal lung using CT data, thoracic specialists may be able to make better functional risk assessments, especially for patients who cannot undergo spirometry, according to chest surgeons from Yamaguchi University Graduate School of Medicine.

Spirometry, one of the first tests performed on individuals with lung disease, measures the extent to which bronchial tubes have narrowed. A whole lung CT is performed as part of the routine workup of lung cancer patients for whom surgery is planned. It is used to identify intrapulmonary small metastases and regional lymph node swelling, to visualize anatomical variations of the pulmonary bronchovasculature, and to make a structural assessment to identify the presence or absence of underlying lung diseases.

The researchers state that valuable information can be obtained by defining the threshold CT attenuation values in the normal lung and the diseased lung to determine their volumes. They developed regression equations to estimate forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV₁) using parameters obtained by quantitative CT and the demographic variables of a patient. They tested the equations in 290 patients with favorable pulmonary function who underwent major lung resection at the hospital over a seven year period. Their findings were validated with a similar group of 100 patients who underwent surgery over 12 months at a referral hospital.

Lead author Kazuhito Ueda, MD, and colleagues explained the team used three-dimensional (3D) volume rendering software to create lung images, and applied threshold limits to segment both whole lungs and to exclude the soft tissue surrounding the lungs, large vessels, atelectasis, fibrosis and tumors within the lung. They defined the total lung volume (TLV) as the volume of the whole lung (-600 to -1,024 Hounsfield Units), which they divided into an emphysematous lung area and the normal lung fields. The emphysematous lung volume (ELV) was defined as the sum of the emphysematous area of the whole lung.

Regression equations were applied and analyzed with patient demographic variables. The authors reported that total lung volume and ELV/TLV (which represents the extent of pulmonary emphysema) was significantly higher in male patients and patients with a smoking history. TLV was positively correlated with ELV/TLV. The authors stated that a higher ELV/TLV value was associated with the prolongation of the duration of chest tube drainage, and that lung cancer recurrence was predominantly found in patients with higher ELV/TLV values, regardless of their surgical outcomes. For these reasons, “a comprehensive assessment using both TLV and ELV is indispensable in the estimation of the pulmonary function,” they wrote.

The authors also reported that both actual and calculated postoperative percentage of predicted forced expiratory volume in 1 second (ppo%FEV₁) were significant predictors of postoperative cardiopulmonary complications. Complications included pneumonia, acute respiratory distress syndrome, empyema, atelectasis, and prolonged mechanical ventilation in the patient cohort.

The analysis showed that total lung capacity (TLC) was significantly correlated TLV. The authors believe that “the measurement of TLV on quantitative CT may be beneficial because the residual volume and the residual volume index can be estimated without the measurement of TLC.” They explained that the estimated residual volume was predictive of the volume reduction effect after lobectomy, and that the residual volume index was useful as a predictive marker of the response in patients with lung cancer and airflow obstruction to bronchodilators.

REFERENCE

1. Ueda K, Murakami J, Tanaka T, et al. Preoperative risk assessment with computed tomography in patients undergoing lung cancer surgery. J Thorac Dis. 2018;10(7):4101-4108.