Is Thoracic CT Performed Often Enough?

Abstract

In a recent editorial in Chest,1DiMarco AF, Briones B. Is chest CT performed too often?.Chest. 1993; 103: 985-986Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar DiMarco and Briones questioned whether thoracic CT is being overutilized. Despite acknowledging a role for CT in evaluating the mediastinum, nodules, interstitial lung disease, and bronchiectasis, these authors state that in their judgment specific indications for the use of CT remain “vague” and the utility of CT in enhancing patient-care decisions is “unclear.”These observations ignore more than a decade's worth of research documenting the clinical value of thoracic CT.2Naidich DP, Zerhouni EA, Siegelman SS. CT/MR of the Thorax. 2nd Ed. Raven Press, New York1991Google Scholar,3Weinberger SE. Recent advances in pulmonary medicine, part 1.N Engl J Med. 1993; 328: 1389-1397Crossref PubMed Scopus (35) Google Scholar This research has clearly demonstrated CT to have a profound impact on diagnosis and patient management. Computed tomography has proved especially helpful when problems are identified but unresolved by plain films. Specific indications for the use of CT in this setting include evaluation of abnormal mediastinal contours, in particular to differentiate normal variants from pathologic entities, including both benign and malignant disease; to further define and characterize solitary or focal parenchymal abnormalities, including the use of CT densitometry to determine the presence of calcification within solitary pulmonary nodules, and to evaluate complex pleural and parenchymal pathology, especially to differentiate lung abscesses from an empyema.4Epstein DM, Stephenson LW, Gefter WB, van der Voorde F, Aronchik JM, Miller WT. Value of CT in the preoperative assessment of lung cancer: a survey of thoracic surgeons.Radiology. 1986; 161: 423-427Crossref PubMed Scopus (35) Google Scholar, 5Zerhouni EA, Stitik FP, Siegelman SS, Computed tomography of the pulmonary nodule: a national cooperative study.Radiology. 1986; 160: 319-327Crossref PubMed Scopus (294) Google Scholar, 6Leung AN, Müller NL, Miller RR. CT in differential diagnosis of diffuse pleural disease.AJR. 1990; 154: 487-492Crossref PubMed Scopus (403) Google Scholar More recently, high-resolution CT has emerged as a revolutionary method with well defined indications in the evaluation of diffuse infiltrative lung disease.7Webb WR, Muller NL, Naidich DP. High-resolution CT of the lung. Raven Press, New York1992Google ScholarComputed tomography has also been shown to be efficacious in evaluating patients suspected of having occult intrathoracic pathologic condition, such as thymoma in patients with myasthenia gravis. Additional common indications in this category include suspected metastatic disease, including occult mediastinal disease, as well as lymphangitic carcinoma, fever of unknown origin, especially in the immunocompromised population, and unexplained symptoms such as dyspnea or hemoptysis.8Davis S. CT evaluation for pulmonary metastases in patients with extrathoracic malignancy.Radiology. 1987; 180: 1-12Crossref Scopus (177) Google Scholar, 9Kuhlman JE, Fishman EK, Burch PA, Karp JE, Zerhouni EA, Siegelman SS. Invasive pulmonary aspergillosis in acute leukemia: the contribution of CT to early diagnosis and aggressive management.Chest. 1987; 92: 95-99Crossref PubMed Scopus (141) Google Scholar, 10Millar AB, Boothroyd AE, Edwards D, Hetzel MR. The role of computed tomography (CT) in the investigation of unexplained haemoptysis.Respir Med. 1992; 86: 39-44Abstract Full Text PDF PubMed Scopus (69) Google ScholarDiMarco and Briones1 also raise questions concerning the risk of ionizing radiation. It is axiomatic that the indications for the use of ionizing radiation always need to be weighed against the potential risks of exposure.11Naidich DP, Marshall CH, Gribben C, Abrams RS, McCauley DI. Low-dose CT of lungs: preliminary observations.Radiology. 1990; 175: 721-731Crossref PubMed Scopus (274) Google Scholar,12Zwirewick CV, Mayo JR, Müller NL. Low-dose high-resolution CT of lung parenchyma.Radiology. 1992; 189: 413-417Google Scholar This determination, however, requires informed and responsible evaluation. Most important, it is necessary to differentiate between the effects of radiation limited to a single part of the body from the effects of whole-body radiation. Even if one accepts the estimates proposed by Beir V (and these remain controversial), the data cited by DiMarco and Briones reflect the effects of whole-body radiation.13National Research Council Committee on the Biological Effects of Ionizing Radiations.Health effects of exposure to low levels of ionizing radiations (BEIR V). National Academy Press, Washington, DC1990Google Scholar,14Hendee WR. Estimation of radiation risks: BEIR V and its significance for medicine.JAMA. 1992; 268: 620-624Crossref PubMed Scopus (57) Google Scholar Radiation risk is considerably greater, per unit dose, for whole body exposure than when only a part of the body is exposed. Radiation risk in the chest is further reduced because there is little active marrow in the adult bony thorax, and lung tissue is relatively insensitive to radiation-induced carcinogenic transformation. Similarly, comparisons between the effects of ionizing radiation and those resulting from radiation exposure to uranium, as suggested, are also misleading. Uranium is deposited directly into the lung, has radiations other than photons, and localizes to small portions of the lung which are continuously radiated.DiMarco and Briones’1 suggestion that the dose for high-resolution CT may be equivalent to 500 chest radiographs is misguided.10Millar AB, Boothroyd AE, Edwards D, Hetzel MR. The role of computed tomography (CT) in the investigation of unexplained haemoptysis.Respir Med. 1992; 86: 39-44Abstract Full Text PDF PubMed Scopus (69) Google Scholar, 11Naidich DP, Marshall CH, Gribben C, Abrams RS, McCauley DI. Low-dose CT of lungs: preliminary observations.Radiology. 1990; 175: 721-731Crossref PubMed Scopus (274) Google Scholar, 12Zwirewick CV, Mayo JR, Müller NL. Low-dose high-resolution CT of lung parenchyma.Radiology. 1992; 189: 413-417Google Scholar, 13National Research Council Committee on the Biological Effects of Ionizing Radiations.Health effects of exposure to low levels of ionizing radiations (BEIR V). National Academy Press, Washington, DC1990Google Scholar, 14Hendee WR. Estimation of radiation risks: BEIR V and its significance for medicine.JAMA. 1992; 268: 620-624Crossref PubMed Scopus (57) Google Scholar, 15Mayo JR, Webb WR, High-resolution CT of the lungs: an optimal approach.Radiology. 1987; 163: 507-510Crossref PubMed Scopus (201) Google Scholar, 16Mayo JR, Jackson SA, Muller NL. High-resolution CT of the chest: radiation dose.AJR. 1993; 160: 479-481Crossref PubMed Scopus (96) Google Scholar, 17Nishizawa K, Maruyama T, Takayama M, Okada M, Hachiya J, Furuya Y. Determination of organ doses and effective dose equivalents from computed tomographic examination.Br J Radiol. 1991; 64: 20-28Crossref PubMed Scopus (79) Google Scholar This determination is based exclusively on theoretical calculations extrapolated from a single phantom study based on the maximal dose a patient could theoretically receive.16Mayo JR, Jackson SA, Muller NL. High-resolution CT of the chest: radiation dose.AJR. 1993; 160: 479-481Crossref PubMed Scopus (96) Google Scholar What is the radiation dose resulting from routine clinical thoracic CT? The effective radiation dose of conventional CT of the chest, using 10-mm-thick sections performed at 10 mm intervals, is approximately 7 mSv.17Nishizawa K, Maruyama T, Takayama M, Okada M, Hachiya J, Furuya Y. Determination of organ doses and effective dose equivalents from computed tomographic examination.Br J Radiol. 1991; 64: 20-28Crossref PubMed Scopus (79) Google Scholar High-resolution CT, consisting of 1-to 2-mm-thick sections performed at 10 mm intervals, has an effective radiation dose only 10 to 20 percent that of conventional CT.16Mayo JR, Jackson SA, Muller NL. High-resolution CT of the chest: radiation dose.AJR. 1993; 160: 479-481Crossref PubMed Scopus (96) Google Scholar By comparison, the combined effective radiation dose of a posteroanterior (PA) and lateral chest radiograph is 0.15 mSv.18Shrimpton PC, Wall BF, Jones DG, Fisher ES, Hillier MC, Kendall GM. A national survey of doses to patients undergoing a selection of routine x-ray examinations in English hospitals. National Radiological Protection Board publication NRPB-R200, Chilton, England1986Google Scholar,19Geleigns J, Broerse JJ, Julius HW, Vrooman HA, Zoetelief J, Zweers D, AMBER and conventional chest radiography: comparison of radiation dose and image quality.Radiology. 1992; 185: 719-723Crossref PubMed Scopus (10) Google Scholar This means that the effective radiation dose of conventional CT is approximately equal to 50 PA and lateral radiographs, while a high-resolution CT study is equivalent to only 5 to 10 PA and lateral radiographs (not 500!). More recently, it has been shown that the dose even of a standard 10-mm-thick CT study can be reduced approximately tenfold by reducing the mAs without sacrificing lung parenchymal detail.11Naidich DP, Marshall CH, Gribben C, Abrams RS, McCauley DI. Low-dose CT of lungs: preliminary observations.Radiology. 1990; 175: 721-731Crossref PubMed Scopus (274) Google Scholar Placed in perspective, the effective radiation dose of high-resolution CT of the chest is less than 30 percent of the average annual effective dose that all individuals receive due to natural radiation in North America.13National Research Council Committee on the Biological Effects of Ionizing Radiations.Health effects of exposure to low levels of ionizing radiations (BEIR V). National Academy Press, Washington, DC1990Google Scholar,19Geleigns J, Broerse JJ, Julius HW, Vrooman HA, Zoetelief J, Zweers D, AMBER and conventional chest radiography: comparison of radiation dose and image quality.Radiology. 1992; 185: 719-723Crossref PubMed Scopus (10) Google Scholar Although more difficult to calculate, it also should be taken into account that CT frequently obviates more traditional methods of diagnosis associated with ionizing radiation, including whole lung and 55° oblique tomography, as well as fluoroscopy associated with angiography, bronchography, and even bronchoscopy.Is thoracic CT performed too often? In our judgment, thoracic CT is more likely underutilized than the opposite! Appropriately integrated into the overall decision making process, in our experience, CT consistently has proved cost-effective by expediting timely diagnosis, serving as a roadmap for diagnostic procedures, especially bronchoscopy, avoiding unnecessary diagnostic and/or invasive procedures, and simplifying follow-up evaluation. It may further be anticipated that the indications for the use of CT will continue to expand as further technologic breakthroughs, including spiral and ultrafast CT become more widely available.20Costello P, Anderson W, Blume D. Pulmonary nodule: evaluation with spiral volumetric CT.Radiology. 1991; 179: 875-876Crossref PubMed Scopus (126) Google Scholar,21Hanada S, Takamiya M, Kimura K, Imakita S, Nakajima N, Naito H. Type A aortic dissection: evaluation with ultrafast CT.Radiology. 1992; 183: 155-158Crossref PubMed Scopus (32) Google Scholar In a recent editorial in Chest,1DiMarco AF, Briones B. Is chest CT performed too often?.Chest. 1993; 103: 985-986Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar DiMarco and Briones questioned whether thoracic CT is being overutilized. Despite acknowledging a role for CT in evaluating the mediastinum, nodules, interstitial lung disease, and bronchiectasis, these authors state that in their judgment specific indications for the use of CT remain “vague” and the utility of CT in enhancing patient-care decisions is “unclear.” These observations ignore more than a decade's worth of research documenting the clinical value of thoracic CT.2Naidich DP, Zerhouni EA, Siegelman SS. CT/MR of the Thorax. 2nd Ed. Raven Press, New York1991Google Scholar,3Weinberger SE. Recent advances in pulmonary medicine, part 1.N Engl J Med. 1993; 328: 1389-1397Crossref PubMed Scopus (35) Google Scholar This research has clearly demonstrated CT to have a profound impact on diagnosis and patient management. Computed tomography has proved especially helpful when problems are identified but unresolved by plain films. Specific indications for the use of CT in this setting include evaluation of abnormal mediastinal contours, in particular to differentiate normal variants from pathologic entities, including both benign and malignant disease; to further define and characterize solitary or focal parenchymal abnormalities, including the use of CT densitometry to determine the presence of calcification within solitary pulmonary nodules, and to evaluate complex pleural and parenchymal pathology, especially to differentiate lung abscesses from an empyema.4Epstein DM, Stephenson LW, Gefter WB, van der Voorde F, Aronchik JM, Miller WT. Value of CT in the preoperative assessment of lung cancer: a survey of thoracic surgeons.Radiology. 1986; 161: 423-427Crossref PubMed Scopus (35) Google Scholar, 5Zerhouni EA, Stitik FP, Siegelman SS, Computed tomography of the pulmonary nodule: a national cooperative study.Radiology. 1986; 160: 319-327Crossref PubMed Scopus (294) Google Scholar, 6Leung AN, Müller NL, Miller RR. CT in differential diagnosis of diffuse pleural disease.AJR. 1990; 154: 487-492Crossref PubMed Scopus (403) Google Scholar More recently, high-resolution CT has emerged as a revolutionary method with well defined indications in the evaluation of diffuse infiltrative lung disease.7Webb WR, Muller NL, Naidich DP. High-resolution CT of the lung. Raven Press, New York1992Google Scholar Computed tomography has also been shown to be efficacious in evaluating patients suspected of having occult intrathoracic pathologic condition, such as thymoma in patients with myasthenia gravis. Additional common indications in this category include suspected metastatic disease, including occult mediastinal disease, as well as lymphangitic carcinoma, fever of unknown origin, especially in the immunocompromised population, and unexplained symptoms such as dyspnea or hemoptysis.8Davis S. CT evaluation for pulmonary metastases in patients with extrathoracic malignancy.Radiology. 1987; 180: 1-12Crossref Scopus (177) Google Scholar, 9Kuhlman JE, Fishman EK, Burch PA, Karp JE, Zerhouni EA, Siegelman SS. Invasive pulmonary aspergillosis in acute leukemia: the contribution of CT to early diagnosis and aggressive management.Chest. 1987; 92: 95-99Crossref PubMed Scopus (141) Google Scholar, 10Millar AB, Boothroyd AE, Edwards D, Hetzel MR. The role of computed tomography (CT) in the investigation of unexplained haemoptysis.Respir Med. 1992; 86: 39-44Abstract Full Text PDF PubMed Scopus (69) Google Scholar DiMarco and Briones1 also raise questions concerning the risk of ionizing radiation. It is axiomatic that the indications for the use of ionizing radiation always need to be weighed against the potential risks of exposure.11Naidich DP, Marshall CH, Gribben C, Abrams RS, McCauley DI. Low-dose CT of lungs: preliminary observations.Radiology. 1990; 175: 721-731Crossref PubMed Scopus (274) Google Scholar,12Zwirewick CV, Mayo JR, Müller NL. Low-dose high-resolution CT of lung parenchyma.Radiology. 1992; 189: 413-417Google Scholar This determination, however, requires informed and responsible evaluation. Most important, it is necessary to differentiate between the effects of radiation limited to a single part of the body from the effects of whole-body radiation. Even if one accepts the estimates proposed by Beir V (and these remain controversial), the data cited by DiMarco and Briones reflect the effects of whole-body radiation.13National Research Council Committee on the Biological Effects of Ionizing Radiations.Health effects of exposure to low levels of ionizing radiations (BEIR V). National Academy Press, Washington, DC1990Google Scholar,14Hendee WR. Estimation of radiation risks: BEIR V and its significance for medicine.JAMA. 1992; 268: 620-624Crossref PubMed Scopus (57) Google Scholar Radiation risk is considerably greater, per unit dose, for whole body exposure than when only a part of the body is exposed. Radiation risk in the chest is further reduced because there is little active marrow in the adult bony thorax, and lung tissue is relatively insensitive to radiation-induced carcinogenic transformation. Similarly, comparisons between the effects of ionizing radiation and those resulting from radiation exposure to uranium, as suggested, are also misleading. Uranium is deposited directly into the lung, has radiations other than photons, and localizes to small portions of the lung which are continuously radiated. DiMarco and Briones’1 suggestion that the dose for high-resolution CT may be equivalent to 500 chest radiographs is misguided.10Millar AB, Boothroyd AE, Edwards D, Hetzel MR. The role of computed tomography (CT) in the investigation of unexplained haemoptysis.Respir Med. 1992; 86: 39-44Abstract Full Text PDF PubMed Scopus (69) Google Scholar, 11Naidich DP, Marshall CH, Gribben C, Abrams RS, McCauley DI. Low-dose CT of lungs: preliminary observations.Radiology. 1990; 175: 721-731Crossref PubMed Scopus (274) Google Scholar, 12Zwirewick CV, Mayo JR, Müller NL. Low-dose high-resolution CT of lung parenchyma.Radiology. 1992; 189: 413-417Google Scholar, 13National Research Council Committee on the Biological Effects of Ionizing Radiations.Health effects of exposure to low levels of ionizing radiations (BEIR V). National Academy Press, Washington, DC1990Google Scholar, 14Hendee WR. Estimation of radiation risks: BEIR V and its significance for medicine.JAMA. 1992; 268: 620-624Crossref PubMed Scopus (57) Google Scholar, 15Mayo JR, Webb WR, High-resolution CT of the lungs: an optimal approach.Radiology. 1987; 163: 507-510Crossref PubMed Scopus (201) Google Scholar, 16Mayo JR, Jackson SA, Muller NL. High-resolution CT of the chest: radiation dose.AJR. 1993; 160: 479-481Crossref PubMed Scopus (96) Google Scholar, 17Nishizawa K, Maruyama T, Takayama M, Okada M, Hachiya J, Furuya Y. Determination of organ doses and effective dose equivalents from computed tomographic examination.Br J Radiol. 1991; 64: 20-28Crossref PubMed Scopus (79) Google Scholar This determination is based exclusively on theoretical calculations extrapolated from a single phantom study based on the maximal dose a patient could theoretically receive.16Mayo JR, Jackson SA, Muller NL. High-resolution CT of the chest: radiation dose.AJR. 1993; 160: 479-481Crossref PubMed Scopus (96) Google Scholar What is the radiation dose resulting from routine clinical thoracic CT? The effective radiation dose of conventional CT of the chest, using 10-mm-thick sections performed at 10 mm intervals, is approximately 7 mSv.17Nishizawa K, Maruyama T, Takayama M, Okada M, Hachiya J, Furuya Y. Determination of organ doses and effective dose equivalents from computed tomographic examination.Br J Radiol. 1991; 64: 20-28Crossref PubMed Scopus (79) Google Scholar High-resolution CT, consisting of 1-to 2-mm-thick sections performed at 10 mm intervals, has an effective radiation dose only 10 to 20 percent that of conventional CT.16Mayo JR, Jackson SA, Muller NL. High-resolution CT of the chest: radiation dose.AJR. 1993; 160: 479-481Crossref PubMed Scopus (96) Google Scholar By comparison, the combined effective radiation dose of a posteroanterior (PA) and lateral chest radiograph is 0.15 mSv.18Shrimpton PC, Wall BF, Jones DG, Fisher ES, Hillier MC, Kendall GM. A national survey of doses to patients undergoing a selection of routine x-ray examinations in English hospitals. National Radiological Protection Board publication NRPB-R200, Chilton, England1986Google Scholar,19Geleigns J, Broerse JJ, Julius HW, Vrooman HA, Zoetelief J, Zweers D, AMBER and conventional chest radiography: comparison of radiation dose and image quality.Radiology. 1992; 185: 719-723Crossref PubMed Scopus (10) Google Scholar This means that the effective radiation dose of conventional CT is approximately equal to 50 PA and lateral radiographs, while a high-resolution CT study is equivalent to only 5 to 10 PA and lateral radiographs (not 500!). More recently, it has been shown that the dose even of a standard 10-mm-thick CT study can be reduced approximately tenfold by reducing the mAs without sacrificing lung parenchymal detail.11Naidich DP, Marshall CH, Gribben C, Abrams RS, McCauley DI. Low-dose CT of lungs: preliminary observations.Radiology. 1990; 175: 721-731Crossref PubMed Scopus (274) Google Scholar Placed in perspective, the effective radiation dose of high-resolution CT of the chest is less than 30 percent of the average annual effective dose that all individuals receive due to natural radiation in North America.13National Research Council Committee on the Biological Effects of Ionizing Radiations.Health effects of exposure to low levels of ionizing radiations (BEIR V). National Academy Press, Washington, DC1990Google Scholar,19Geleigns J, Broerse JJ, Julius HW, Vrooman HA, Zoetelief J, Zweers D, AMBER and conventional chest radiography: comparison of radiation dose and image quality.Radiology. 1992; 185: 719-723Crossref PubMed Scopus (10) Google Scholar Although more difficult to calculate, it also should be taken into account that CT frequently obviates more traditional methods of diagnosis associated with ionizing radiation, including whole lung and 55° oblique tomography, as well as fluoroscopy associated with angiography, bronchography, and even bronchoscopy. Is thoracic CT performed too often? In our judgment, thoracic CT is more likely underutilized than the opposite! Appropriately integrated into the overall decision making process, in our experience, CT consistently has proved cost-effective by expediting timely diagnosis, serving as a roadmap for diagnostic procedures, especially bronchoscopy, avoiding unnecessary diagnostic and/or invasive procedures, and simplifying follow-up evaluation. It may further be anticipated that the indications for the use of CT will continue to expand as further technologic breakthroughs, including spiral and ultrafast CT become more widely available.20Costello P, Anderson W, Blume D. Pulmonary nodule: evaluation with spiral volumetric CT.Radiology. 1991; 179: 875-876Crossref PubMed Scopus (126) Google Scholar,21Hanada S, Takamiya M, Kimura K, Imakita S, Nakajima N, Naito H. Type A aortic dissection: evaluation with ultrafast CT.Radiology. 1992; 183: 155-158Crossref PubMed Scopus (32) Google Scholar