Screening for cancer with computed tomography

Dose reduction strategies for thoracic multidetector computed tomography: background, current issues, and recommendations

This review will summarize the current background knowledge about radiation exposure related to thoracic computed tomography (CT). It will also review the historical development in this area. This will be followed by a summary of current efforts to reduce dose with respect to predefined clinical indications. Finally, the review will indicate future strategies for further dose reduction in thoracic CT imaging and give practical recommendations for everyday use.

Pleural nodule identification in low-dose and thin-slice lung computed tomography

A completely automated system for the identification of pleural nodules in low-dose and thin-slice computed tomography (CT) of the lung has been developed. The directional-gradient concentration method has been applied to the pleura surface and combined with a morphological opening-based procedure to generate a list of nodule candidates. Each nodule candidate is characterized by 12 morphological and textural features, which are analyzed by a rule-based filter and a neural classifier. This detection system has been developed and validated on a dataset of 42 annotated CT scans. The k-fold cross validation has been used to evaluate the neural classifier performance. The system performance variability due to different ground truth agreement levels is discussed. In particular, the poor 44% sensitivity obtained on the ground truth with agreement level 1 (nodules annotated by only one radiologist) with six FP per scan grows up to the 72% if the underlying ground truth is changed to the agreement level 2 (nodules annotated by two radiologists).

FDG-pet in paraneoplastic syndromes

Paraneoplastic syndromes are rare disorders, but recognition is important because clinical manifestations of paraneoplastic syndromes may precede those of the underlying malignancy by months or even years. As tumor therapy still is the mainstay of treatment for paraneoplastic syndromes, early diagnosis of the initial tumor or its recurrence is of utmost clinical importance. For finding the associated tumor, the combined use of FDG-PET and CT seems to have the highest sensitivity and may contribute to accurately distinguishing a true tumor or recurrence from benign lesions or physiologic or inflammatory uptake. Further, this approach helps localize the tumor for further management of the patient such as surgery or more invasive diagnostic procedures. Cerebral FDG-PET proved to confirm paraneoplastic encephalitis and may help monitor tumor therapy.

Management of Patients with Small Pulmonary Nodules: A Survey of Radiologists, Pulmonologists, and Thoracic Surgeons

OBJECTIVE

The objective of our study was to survey recommendations for the management of small pulmonary nodules found on helical CT from radiologists, pulmonologists, and thoracic surgeons.

MATERIALS AND METHODS

We surveyed 774 radiologists, 623 pulmonologists, and 101 thoracic surgeons. All are members of an associated Austrian scientific society and were asked for their recommendations in 13 hypothetical cases. Statistical analysis was focused on possible differences between medical specialities, residents and fellows, and male and female doctors and on a possible influence of the number of years in training or in medical practice.

RESULTS

Complete surveys were returned from 91 radiologists, 74 pulmonologists, and 12 thoracic surgeons. The most frequent recommendation from radiologists was follow-up, whereas the most frequent recommendation from pulmonologists and surgeons was biopsy. The most frequently advised CT follow-up period was 3 months. Whereas thoracic surgeons preferred video-assisted thoracoscopy, radiologists and pulmonologists recommended less invasive procedures (bronchoscopy, CT-guided biopsy) to gain a specific diagnosis.

CONCLUSION

There are significant differences in the management of small pulmonary nodules among radiologists, pulmonologists, and thoracic surgeons. Whereas radiologists tend to recommend short-term follow-up, pulmonologists and thoracic surgeons prefer a more aggressive approach, especially in patients with a higher likelihood of malignancy.

Early Detection of Lung Cancer

The overall 5-year survival of lung cancer is only 10% in Europe and 15% in the United States, and progress in curative treatments during the last 20 years has been modest. Late diagnosis of extensive disease is the main reason of failure. Early detection with low-dose spiral computed tomography (CT) is one of the most promising development of clinical research, and continuous improvements in technology can make this instrument more effective than mammography in breast cancer detection. In order to prove the benefit of early detection by reduction of lung cancer mortality, we need to enroll large numbers of high-risk individuals in multicentric prospective randomized trials combining primary prevention by smoking cessation with diagnostic intervention with low-dose spiral CT, optimal management of cancer and minimum damage for healthy individuals. Molecular biology research within early detection trials, combining genomic and proteomic analysis of blood and sputum, may improve the differential diagnosis, define the individual risk of cancer incidence and failure, and help target therapies on the basis of biologic profile.

Incidental lung cancers identified at coronial autopsy: implications for overdiagnosis of lung cancer by screening

BACKGROUND

The extent to which overdiagnosis occurs in lung cancer screening programmes has been debated. Overdiagnosis refers to the detection by screening of cancers that would not have become clinically apparent or symptomatic before that individual died of other causes.

METHODS

A retrospective review of coronial autopsies performed in Victoria between April 1991 and February 2002 was conducted to determine the rate of incidental lung cancer in individuals who died of natural causes.

RESULTS

A total of 24,708 autopsy reports were searched electronically. We estimated that in 56% of these death was from natural causes. Amongst individuals who died naturally there were 167 cases of lung cancer, 47 of these were incidental including five carcinoid tumours, three small cell tumours, 11 cases of carcinoma in situ and 28 invasive nonsmall cell lung cancers. Of the incidental invasive nonsmall cell lung cancers, 86% were stage I.

CONCLUSIONS

Although incidental lung cancer is uncommon, there are some lung cancers that remain undetected during life and do not contribute to death. These findings support the hypothesis that some lung cancers detected by screening may never progress to cause symptoms or death in that individual's lifetime and therefore may be overdiagnosed by screening.

Flat panel detector-based volumetric CT: prototype evaluation with volumetry of small artificial nodules in a pulmonary phantom

PURPOSE

To evaluate amorphous silicone-based flat panel detector volumetric CT (VCT) in volumetric assessment of small nodules in a pulmonary phantom, and to perform comparative experiments with 4-row multislice CT (MSCT).

MATERIALS AND METHODS

Seventy synthetic nodules (volume range (VR): 0.99-185.77 mm; estimated diameter range (ED): 1.4-7.8 mm) were scanned in spherical shape and after iso-volumetric deformation with VCT and MSCT using 0.63 mm (MSCT I) and 1.25 mm (MSCT II) collimations. Measured volumes and percent measurement errors (PME) were compared between the 3 CT modes before and after nodule deformation. For each measurement pair before and after deformation, the post-deformation relative volumetric inaccuracy (RIA) was determined. Volume, PME, and RIA differences were tested using Wilcoxon and Friedman methods.

RESULTS

The volumes of the smallest nodules (VR = 0.99-2.83 mm, ED = 1.4-1.9 mm) were computable only from VCT scans. In VCT, measured volumes and PMEs before and after deformation differed significantly less compared with MSCT (VCT: P = 0.06 and 0.56, respectively; MSCT I: P = 0.0012 and 0.006, respectively; and MSCT II: P < 0.0001 for measured volumes and PMEs). In VCT PMEs of 5.51-32.21 mm nodules (ED = 2.4-4.1 mm) before and after deformation were significantly below MSCT (VCT averages = 1.43-1.91% and 1.98-3.48%, for spherical and deformed nodules, respectively; MSCT I averages = 9.97-26.1% and 12.16-38.10%, respectively; MSCT II averages = 17.79-46.18 and 18.14-54.66%, respectively, P < 0.0001) and RIAs in VCT were significantly below MSCT (VCT: 0.50-2.62%, MSCT I: 3.35-15.97%, and MSCT II: 4.29-18.46%; P = 0.0001-0.0039).

CONCLUSION

VCT volumetry is highly accurate in volumetry of smallest nodules with estimated diameters of 1.4-4.1 mm.

Whole‐body computed tomography screening: looking for trouble?

The benefits of whole-body CT screening need to be carefully weighed against the risks.

Thoracic surgical operations in patients enrolled in a computed tomographic screening trial

OBJECTIVE

Screening for lung cancer with computed tomography may detect cancers at an earlier stage but may also result in overdiagnosis. We reviewed the thoracic surgical operations performed on patients enrolled in our computed tomographic screening program.

METHODS

From January 1999 through December 2002, screening computed tomography for lung cancer was performed annually on 1520 participants. All participants were at least 50 years old and smoked more than 20 pack/y. We found 3130 indeterminate pulmonary nodules in 1112 participants (73%). Fifty-five participants (3.6%) underwent 60 thoracic operations for a variety of indications. The medical records of these 55 patients were reviewed.

RESULTS

Indications for operation included suspicious pulmonary nodules, mediastinal adenopathy, and a spontaneous pneumothorax. Operations performed included a lobectomy in 37 cases, wedge resection in 11, segmentectomy in 6, video-assisted thoracoscopic surgical talc pleurodesis in 1, bilobectomy in 2, mediastinoscopy in 2, and anterior mediastinotomy in 1. Benign disease was found in 10 patients (18.1%), and lung cancer was found in 45 (81.9%), 2 of whom had metachronous lung cancers. Cell types were adenocarcinoma in 15 cancers, bronchioloalveolar cell carcinoma in 13, squamous cell in 13, carcinoid in 2, small cell in 2, and large cell and undifferentiated non-small cell in 1 case each. Twenty-eight cancers were classified as stage IA, 4 as IB, 4 as IIA, 1 as IIB, 4 as IIIA, 3 as IIIB, 1 as IV, and 2 as limited small cell carcinoma. Complications occurred in 27% of patients. Operative mortality was 1.7%.

CONCLUSION

Computed tomographic screening finds a large number of indeterminate pulmonary nodules in smokers 50 years old or older, most of which are observed and not operated on. Although 47 cancers were detected thus far in this highly selected group of patients, this represents only 1.5% of the pulmonary nodules identified.

Multislice CT: update on radiation and screening

With ever-expanding applications, increasing availability, and accessibility of CT scanners, concerns have been raised about radiation exposure associated with CT scanning. Global statistics and projections suggest increasing use of CT scanning and its contribution to radiation exposure is a cause for concern. Several strategies based on modulation of scanning parameters and technologic improvisations have been developed in an effort to reduce associated radiation dose. This article discusses the basis for rising concern regarding radiation dose associated with CT scanning. The fundamentals of CT dose estimation are described along with strategies that aim to reduce radiation dose associated with CT scanning based on patient characteristics, study indications, and technological innovations.

CT Screening — whole-body and targeted

At present, the Australasian College of Physical Scientists and Engineers in Medicine does not support the practice of self-referred whole-body CT screening of asymptomatic patients because: The procedure involves a non-trivial radiation dose, which assumes even greater significance in the context of an ongoing screening programme; There is a high likelihood of false positives requiring further intervention with its attendant risks; and There is no proven evidence to date that early detection of life-threatening disease by CT has a significant positive effect on patient outcome. The ACPSEM will continue to monitor scientific studies concerning this procedure.

Is opportunistic disease prevention in the consultation ethically justifiable?

Medical resources are increasingly shifting from making patients better to preventing them from becoming ill. Genetic testing is likely to extend the list of conditions that can be screened for. Is it time to stop and consider whom we screen and how we approach it?

Early lung-cancer detection with spiral CT and positron emission tomography in heavy smokers: 2-year results

BACKGROUND

Low-dose spiral CT of the chest effectively detects early-stage lung cancer in high-risk individuals. The high rate of benign nodules and issues of making a differential diagnosis are critical factors that currently hamper introduction of large-scale screening programmes. We investigated the efficacy of repeated yearly spiral CT and selective use of positron emission tomography (PET) in a large cohort of high-risk volunteers.

METHODS

We enrolled 1035 individuals aged 50 years or older who had smoked for 20 pack-years or more. All patients underwent annual low-dose CT, with or without PET, for 5 years. Lesions up to 5 mm were deemed non-suspicious and low-dose CT was repeated after 12 months (year 2).

FINDINGS

By year 2, 22 cases of lung cancer had been diagnosed (11 at baseline, 11 at year 2). 440 lung lesions were identified in 298 (29%) participants, and 95 were recalled for high-resolution contrast CT. PET scans were positive in 18 of 20 of the identified cancer cases. Six patients underwent surgical biopsy for benign disease because of false-positive results (6% of recalls, 22% of invasive procedures). Complete resection was achieved in 21 (95%) lung cancers, 17 (77%) were pathological stage I (100% at year 2), and the mean tumour size was 18 mm. There were no interval lung cancers in the 2.5 years of follow-up (average time on study from randomisation to last contact), although 19 individuals were diagnosed with another form of cancer (two deaths and 17 non-fatal admissions).

INTERPRETATION

Combined use of low-dose spiral CT and selective PET effectively detects early lung cancer. Lesions up to 5 mm can be checked again at 12 months without major risks of progression.