Incidental Findings of Pulmonary and Hilar Malignancy by Low-Resolution Computed Tomography Used in Myocardial Perfusion Imaging
Background: Low dose, low-resolution computed tomography (CT) is used for attenuation correction to improve the quality of single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI). Because of its low resolution, these CT images are considered nondiagnostic and are not routinely or uniformly reviewed or interpreted by a cardiologist. On the other hand, low-dose CT has been used for lung cancer screening to reduce lung cancer mortality and is recommended for annual screening of high-risk patients by the US Preventive Services Task Force.
Methods: Siemens Symbia Intevo Excel SPECT/CT scanners, used primarily for cardiac MPI, were used in the study. The study was intended to report incidental findings of pulmonary and hilar malignancy detected by these CT images during cardiac evaluation. It included 1,098 consecutive patients who had SPECT MPI from September 1, 2017 to August 31, 2018. When suspicious pulmonary nodules or abnormalities were identified, primary care providers were notified of the findings and recommendations for further evaluation.
Results: Five patients were found to have lung cancer (all male with substantial smoking history, aged 64-75 years), 1 had mantle cell lymphoma. Six of 1,098 (0.55%) patients were found to have incidental pulmonary/hilar malignancy, which is comparable to the yield (0.65%/year) of detecting lung cancer using low-dose CT for screening in The National Lung Screening Trial.
Conclusions: Routine review and report of incidental findings on low-resolution CT during cardiac MPI by physicians skilled in CT interpretation is necessary to identify incidental but clinically important findings, including malignancies.
Methods
The Siemens’ (Munich, Germany) Symbia Intevo Excel SPECT/CT MPI cameras with dedicated cardiac collimators were used at both the Dwight D. Eisenhower VA Medical Center (VAMC) in Leavenworth, Kansas and Colmery-O'Neil VAMC in Topeka, Kansas. The integrated CT scanner (x-ray tube current 30 to 240 mA; voltage 110 Kv with a 40 kW power generator) has the capability to image up to a 2-slice/rotation, each of 5.0 mm per slice with a scan time of about 30 seconds. The SPECT/CT gamma camera has a low energy (140 KeV), high resolution, parallel hole collimator with IQ SPECT capabilities.
The radiation dose received by the patients were expressed in dose length product (DLP), which reflects the total energy absorbed by the patient and represents integrated dose in terms of the total scan length. Additionally, each patients received 2 injections of Technetium Tc 99m sestamibi (1-day Protocol: 10 mCi rest injection, 30 mCi stress injection: 2-day Protocol for patients weighing > 350 pounds: 30 mCi at rest injection and 30 mCi at stress injection) for myocardial perfusion imaging.
All CT images and cardiac MPI findings were reviewed and reported contemporaneously by 1 of 2 experienced, board-certified radiologists who were blinded to patients’ clinical information except the indication for the cardiac stress testing. When suspicious pulmonary/hilar nodules or masses were detected, these findings and recommendations for further evaluation were conveyed to primary care provider or ordering physician via the electronic health record system.
All CT images were reviewed with cardiac MPI from September 1, 2017 to August 31, 2018. When pulmonary/hilar malignancies were identified, the health records were reviewed. Patients with known history of prior pulmonary malignancy were excluded from the study.
Results
A total of 1,098 patients underwent cardiac MPI during the study period. When the CT imaging and cardiac MPI were reviewed, incidental findings led to the diagnosis of lung cancer in 5 patients and hilar mantle cell lymphoma in 1 patient. Their clinical characteristics, CT findings, and types of malignancies for these 6 patients are summarized in the Table and Figure. Only 0.55% (6 of 1,098) patients were found to have incidental pulmonary/hilar malignancy with the cardiac evaluation low-resolution CT. Four patients with prior, known history of lung cancer were excluded from the study.
For the 6 patients found to have cancer, the average CT radiation dose during the cardiac MPI was 100 mGy-cm (range, 77 -133 mCy-cm). The subsequent chest CT with or without contrast delivered a radiation dose of 726.4 mGy-cm (range, 279.4 - 1,075 mGy-cm).
A total of 79 (7.2%) patients were found to have significant pulmonary nodules that required further evaluation; after CT examination, 32 patients had findings of benign nature and required no further follow-up; the other 47 patients are being followed according to the Fleischner Society 2017 guidelines for pulmonary nodules.11 The follow-up findings on these patients are not within the scope of this report.
Discussion
Although incidental findings on low-resolution CT during cardiac MPI are frequent, clinically significant findings are less common. However, some incidental findings may be of important clinical significance.3-5 A multicenter analysis by Coward and colleagues reported that 2.4% findings on low-resolution CT were significant enough to warrant follow-up tests, but only 0.2% were deemed potentially detrimental to patient outcomes (ie, pathology confirmed malignancies).12 Thus, the authors suggested that routine reporting of incidental findings on low-dose CT images was not beneficial.12,13
