(Radiographics. 2000;20:83-98.)
© RSNA, 2000
Radiation-induced Lung Disease and the Impact of Radiation Methods on Imaging Features
Kyung Joo Park, MD,
Jin Young Chung, MD ,
Mi Son Chun, MD and
Jung Ho Suh, MD
1 From the Departments of Radiology (K.J.P., J.Y.C., J.H.S.) and Therapeutic Radiology (M.S.C.), Ajou University Medical Center, San 5, Wonchon, Paldal, Suwon 442-749, South Korea. Presented as a scientific exhibit at the 1998 RSNA scientific assembly. Received February 24, 1999; revision requested April 6 and received June 2; accepted June 8. Address reprint requests to K.J.P.
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Abstract
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Although radiologic findings in radiation-induced lung disease are well described in the literature, the influence exerted on these findings by different radiation methods is not well understood. Radiation treatment of non–small cell lung cancer varies depending on the location and extent of disease. Irradiation with oblique beam angles results in unusual distribution of radiation-induced lung disease. Small cell lung cancer is treated with irradiation concurrent with or following chemotherapy, and portal arrangements are controversial. In breast cancer, use of tangential beam portals may induce radiation pneumonitis or fibrosis at the peripheral lung anterolaterally. Use of supraclavicular portals may produce lesions in the lung apex that appear similar to pulmonary tuberculosis. In esophageal cancer, radiation portals with a 5–6-cm margin above and below the tumor are generally recommended, and computed tomography (CT) frequently demonstrates radiation-related lung damage adjacent to the mediastinum. In mediastinal tumors, the mantle field includes all the major lymph node regions above the diaphragm. Radiation pneumonitis varies from minimal to extremely marked change in the paramediastinal areas and in both apices. CT is more sensitive to radiation-induced lung disease than chest radiography and demonstrates related changes earlier. Furthermore, it more clearly depicts the precise distribution and pattern of disease. Familiarity with the imaging findings in radiation-induced lung disease produced by different radiation methods will help radiologists interpret abnormalities seen at chest radiography and CT in affected patients.
Index Terms: Lung, effects of irradiation on, 60.47 • Lung neoplasms, therapeutic radiology, 60.1299 • Radiations, injurious effects, complications of therapeutic radiology, 60.47
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Introduction
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Various radiation portals and beam angles are used in the treatment of patients with thoracic malignancies depending on the location, extent, and pathologic diagnosis of the disease. Even different therapists at a given institution may choose different methods of treating the same lesion (1). When pulmonary areas of increased opacity are seen at follow-up radiography in patients treated with radiation therapy, the differential diagnosis includes radiation pneumonitis, local recurrence, lymphangitic spread of tumor, and infectious pneumonitis (2,3). The shape and distribution of radiation-induced lung disease vary with different radiation methods, and because radiation-induced lung changes are usually confined to the irradiated volume (2,4), interpretation of chest radiographs is often difficult without a precise knowledge of the radiation methods used. However, understanding the general principles of radiation technique will aid in the interpretation of images obtained in affected patients.
In this article, we discuss the radiation techniques used to treat various thoracic malignancies including non–small cell lung cancer, small cell lung cancer, breast cancer, esophageal cancer, mediastinal tumors, and head and neck tumors. In addition, we discuss and illustrate the characteristic radiologic features of a spectrum of radiation-induced lung diseases seen with different radiation methods.
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Characteristic Radiologic Features of Radiation-induced Lung Disease
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Two distinct clinical stages are recognized in radiation-induced lung disease: an early, transient stage characterized by radiation pneumonitis and a later stage characterized by chronic radiation fibrosis. Radiation pneumonitis usually occurs about 4–12 weeks after completion of radiation therapy. Fibrous changes take 6–24 months to evolve but usually remain stable after 2 years. Like all other forms of diffuse alveolar damage, lung injury from radiation is divided into three sequential pathologic phases: an exudative phase, an organizing or proliferative phase, and a chronic fibrotic phase (5).
Although there have been reports of extensive radiation pneumonitis occurring outside the treatment portals (6,7), the radiographic changes in radiation pneumonitis are generally confined to the field of irradiation. Initially, there is a diffuse haze in the irradiated region with obscuring of vascular outlines. Patchy consolidations appear and then coalesce to form a relatively sharp edge that conforms to the treatment portals rather than to anatomic boundaries. These manifestations may clear gradually and disappear completely but may lead to fibrous change in cases of severe injury. Chronic radiation fibrosis is indicated by findings of a well-defined area of atelectasis with parenchymal distortion, traction bronchiectasis, mediastinal shifting, or pleural thickening (5,8,9) (Fig 1). Occasionally, a pleural effusion develops on the irradiated side. Typically, this effusion is small and is seen with acute radiation pneumonitis (2).
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Figure 1a. Evolution of radiation-induced lung disease in a 65-year-old man with non-small cell lung cancer. (a) Pretreatment chest radiograph shows a nodule in the left upper lobe (arrow). (b) Radiograph obtained 3 months after completion of radiation therapy shows ill-defined, patchy haziness in the irradiated regions of both upper lungs (arrows). (c, d) Radiographs obtained 6 months (c) and 1 year (d) after completion of therapy demonstrate evolution of the disease with increasing volume loss, homogeneity of opacity, and sharpness of lateral margins.
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Figure 1b. Evolution of radiation-induced lung disease in a 65-year-old man with non-small cell lung cancer. (a) Pretreatment chest radiograph shows a nodule in the left upper lobe (arrow). (b) Radiograph obtained 3 months after completion of radiation therapy shows ill-defined, patchy haziness in the irradiated regions of both upper lungs (arrows). (c, d) Radiographs obtained 6 months (c) and 1 year (d) after completion of therapy demonstrate evolution of the disease with increasing volume loss, homogeneity of opacity, and sharpness of lateral margins.
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Figure 1c. Evolution of radiation-induced lung disease in a 65-year-old man with non-small cell lung cancer. (a) Pretreatment chest radiograph shows a nodule in the left upper lobe (arrow). (b) Radiograph obtained 3 months after completion of radiation therapy shows ill-defined, patchy haziness in the irradiated regions of both upper lungs (arrows). (c, d) Radiographs obtained 6 months (c) and 1 year (d) after completion of therapy demonstrate evolution of the disease with increasing volume loss, homogeneity of opacity, and sharpness of lateral margins.
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Figure 1d. Evolution of radiation-induced lung disease in a 65-year-old man with non-small cell lung cancer. (a) Pretreatment chest radiograph shows a nodule in the left upper lobe (arrow). (b) Radiograph obtained 3 months after completion of radiation therapy shows ill-defined, patchy haziness in the irradiated regions of both upper lungs (arrows). (c, d) Radiographs obtained 6 months (c) and 1 year (d) after completion of therapy demonstrate evolution of the disease with increasing volume loss, homogeneity of opacity, and sharpness of lateral margins.
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Computed tomography (CT) is more sensitive and demonstrates radiation-induced changes earlier than chest radiography (10–13). Furthermore, it is much more useful in evaluating the precise distribution and pattern of the resulting lesion. Findings indicative of fibrosis such as volume loss, architectural distortion, bronchiectasis, and pleural thickening are better demonstrated at CT, and the irradiated and normal areas of the lung are more clearly delineated (5).
Libshitz and Shuman (10) classified the CT appearance of pulmonary abnormalities as (a) ground-glass attenuation or homogeneous consolidation (Fig 2), (b) patchy consolidation within the irradiated lung that does not conform to the shape of the portal (Fig 3), (c) discrete consolidation that conforms to the shape of the portal but does not outline it uniformly (Fig 4a), and (d) solid consolidation that conforms to and totally involves the irradiated portions of the lung (Fig 4b). Presumably, the first and second patterns correspond to the acute exudative phase of radiation-induced injury, the third pattern corresponds to the organizing or proliferative phase with relative sparing of some areas, and the fourth pattern corresponds to the chronic fibrotic phase (5,10,11).
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Figure 2. Non-small cell lung cancer in a 47-year-old man. CT scan obtained 3 months after completion of radiation therapy shows ground-glass attenuation in the irradiated paramediastinal region of the right lung.
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Figure 3. Non-small cell lung cancer in a 55-year-old man. CT scan obtained 4 months after completion of radiation therapy shows patchy consolidation in the irradiated region of the right lung.
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Figure 4a. Adenocarcinoma of the lung in a 50-year-old woman. The patient was treated with a radiation dose of 50 Gy after undergoing right upper and middle lobectomy. (a) CT scan obtained 3 months after completion of therapy shows discrete consolidation in the right lower lobe conforming to the radiation portal. (b) CT scan obtained at the same level 5 months later demonstrates solid consolidation with a sharp, straight lateral edge (arrows).
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Figure 4b. Adenocarcinoma of the lung in a 50-year-old woman. The patient was treated with a radiation dose of 50 Gy after undergoing right upper and middle lobectomy. (a) CT scan obtained 3 months after completion of therapy shows discrete consolidation in the right lower lobe conforming to the radiation portal. (b) CT scan obtained at the same level 5 months later demonstrates solid consolidation with a sharp, straight lateral edge (arrows).
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Technical Factors in Radiation Therapy
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Technical factors that influence the degree of radiation damage to normal tissue include total dose, fractionation and dose rate, irradiated volume, and portals and beam arrangement as well as physical characteristics of the irradiation (5,8). Preexisting lung disease and functional capacity of the portion of lung being irradiated may also be important factors with regard to lung damage from radiation (9,14). Several chemotherapeutic agents potentiate the effects of radiation. Steroids ameliorate radiation pneumonitis, but abrupt termination of steroid therapy may unmask latent radiation injury to the lung (15).
Total Dose
The correlation between radiation dose and the prevalence of radiation damage is not linear; rather, it increases dramatically after a threshold dose is reached (9). Pulmonary damage rarely occurs with total doses less than 20 Gy (16), commonly occurs with doses between 30 and 40 Gy, and almost always occurs with doses over 40 Gy (2). Clinical or radiographic signs of radiation injury may not be seen with subcritical radiation doses.
Fractionation and Dose Rate
Fractionation reduces the biologic impact of radiation. The size and number of the daily dose fractions have a direct bearing on the risk of radiation pneumonitis (9). A recent study showed that administration of a daily dose fraction greater than 2.67 Gy was the most significant factor associated with an increased risk of radiation pneumonitis (17).
Irradiated Lung Volume
Because total doses almost always exceed the critical values (eg, the total dose used for carcinomas typically exceeds 50 Gy), irradiated lung volume is probably the most important factor in symptomatic radiation lung injury (5). When 25% of the lung is irradiated, it is unlikely that symptoms will develop, although pathologic analysis of tissues from irradiated areas may show evidence of damage. When 50% or more of the lung is irradiated, there is a greater prevalence of symptomatic radiation pneumonitis (9).
Portals and Beam Arrangement
Various radiation portals and beam angles are used to treat thoracic malignancies depending on the location, extent, and pathologic diagnosis of the neoplasm. Radiation-induced lung disease conforms to the portals and beam arrangement used for irradiation. Use of lateral or oblique multidirectional portals may increase the risk of radiation pneumonitis (5).
Non–Small Cell Lung Cancer.—In non–small cell lung cancer, the volume to be treated and the configuration of the radiation portals are determined by the size, location, and histologic characteristics of the primary tumor, areas of lymphatic drainage in the hila and mediastinum, and equipment and beam energy available. Typically, treatment portals are designed with a 2-cm margin around any gross tumor seen at posteroanterior radiography and a 1-cm margin around electively treated regional lymph node areas (1).
For upper lobe lesions, portals may include one or both supraclavicular regions and the mediastinum with an inferior margin of 5–6 cm below the carina (Fig 5a, 5b). For middle or lower lobe lesions, the supraclavicular areas are usually excluded when there is no mediastinal lymphadenopathy (Figs 5c, 5d, 6). If there is a gross mediastinal tumor, inclusion of the ipsilateral supraclavicular area within the irradiated volume is recommended (Figs 5d, 7) (1).
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Figure 5a. Portals used for irradiation of lung cancer. (a, b) Portal radiographs demonstrate portals used for irradiation of non-small cell lung cancer in the upper lobes. Note the unilateral (a) and bilateral (b) supraclavicular fields. (c, d) Portal radiographs demonstrate portals used for irradiation of non-small cell lung cancer in the lower lobes. The supraclavicular areas are included if there is a gross mediastinal tumor in the lower lobe (d). (e, f) Portal radiographs demonstrate portals used for irradiation of small cell lung cancer, including a limited portal (e) and a larger portal that includes both hilar regions, the entire mediastinum, and the supraclavicular region (f).
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Figure 5b. Portals used for irradiation of lung cancer. (a, b) Portal radiographs demonstrate portals used for irradiation of non-small cell lung cancer in the upper lobes. Note the unilateral (a) and bilateral (b) supraclavicular fields. (c, d) Portal radiographs demonstrate portals used for irradiation of non-small cell lung cancer in the lower lobes. The supraclavicular areas are included if there is a gross mediastinal tumor in the lower lobe (d). (e, f) Portal radiographs demonstrate portals used for irradiation of small cell lung cancer, including a limited portal (e) and a larger portal that includes both hilar regions, the entire mediastinum, and the supraclavicular region (f).
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Figure 5c. Portals used for irradiation of lung cancer. (a, b) Portal radiographs demonstrate portals used for irradiation of non-small cell lung cancer in the upper lobes. Note the unilateral (a) and bilateral (b) supraclavicular fields. (c, d) Portal radiographs demonstrate portals used for irradiation of non-small cell lung cancer in the lower lobes. The supraclavicular areas are included if there is a gross mediastinal tumor in the lower lobe (d). (e, f) Portal radiographs demonstrate portals used for irradiation of small cell lung cancer, including a limited portal (e) and a larger portal that includes both hilar regions, the entire mediastinum, and the supraclavicular region (f).
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Figure 5d. Portals used for irradiation of lung cancer. (a, b) Portal radiographs demonstrate portals used for irradiation of non-small cell lung cancer in the upper lobes. Note the unilateral (a) and bilateral (b) supraclavicular fields. (c, d) Portal radiographs demonstrate portals used for irradiation of non-small cell lung cancer in the lower lobes. The supraclavicular areas are included if there is a gross mediastinal tumor in the lower lobe (d). (e, f) Portal radiographs demonstrate portals used for irradiation of small cell lung cancer, including a limited portal (e) and a larger portal that includes both hilar regions, the entire mediastinum, and the supraclavicular region (f).
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Figure 5e. Portals used for irradiation of lung cancer. (a, b) Portal radiographs demonstrate portals used for irradiation of non-small cell lung cancer in the upper lobes. Note the unilateral (a) and bilateral (b) supraclavicular fields. (c, d) Portal radiographs demonstrate portals used for irradiation of non-small cell lung cancer in the lower lobes. The supraclavicular areas are included if there is a gross mediastinal tumor in the lower lobe (d). (e, f) Portal radiographs demonstrate portals used for irradiation of small cell lung cancer, including a limited portal (e) and a larger portal that includes both hilar regions, the entire mediastinum, and the supraclavicular region (f).
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Figure 5f. Portals used for irradiation of lung cancer. (a, b) Portal radiographs demonstrate portals used for irradiation of non-small cell lung cancer in the upper lobes. Note the unilateral (a) and bilateral (b) supraclavicular fields. (c, d) Portal radiographs demonstrate portals used for irradiation of non-small cell lung cancer in the lower lobes. The supraclavicular areas are included if there is a gross mediastinal tumor in the lower lobe (d). (e, f) Portal radiographs demonstrate portals used for irradiation of small cell lung cancer, including a limited portal (e) and a larger portal that includes both hilar regions, the entire mediastinum, and the supraclavicular region (f).
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Figure 6a. Squamous cell carcinoma in a 62-year-old man. (a) Pretreatment chest radiograph shows a cavitary mass in the right lower lobe. The patient was treated with a radiation dose of 50 Gy with portals that included lung tissue adjacent to the mass as well as the lower mediastinum (cf Fig 5c). (b) Radiograph obtained 4 months after completion of radiation therapy shows faint, ill-defined areas of increased opacity around the cavitary mass (arrows).
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Figure 6b. Squamous cell carcinoma in a 62-year-old man. (a) Pretreatment chest radiograph shows a cavitary mass in the right lower lobe. The patient was treated with a radiation dose of 50 Gy with portals that included lung tissue adjacent to the mass as well as the lower mediastinum (cf Fig 5c). (b) Radiograph obtained 4 months after completion of radiation therapy shows faint, ill-defined areas of increased opacity around the cavitary mass (arrows).
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Figure 7a. Lung changes in a 41-year-old man with adenocarcinoma treated with mediastinal and supraclavicular radiation portals. (a) Pretreatment chest radiograph shows a mass in the right lower lobe as well as right paratracheal lymph nodes (arrow). (b, c) CT scans obtained 2 months after completion of radiation therapy show patchy consolidation and ground-glass attenuation in the lower lobes (b) and both lung apices (c) conforming to the supraclavicular portals. (d) Chest radiograph obtained 18 months after b and c demonstrates advanced radiation fibrosis in the right lung.
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Figure 7b. Lung changes in a 41-year-old man with adenocarcinoma treated with mediastinal and supraclavicular radiation portals. (a) Pretreatment chest radiograph shows a mass in the right lower lobe as well as right paratracheal lymph nodes (arrow). (b, c) CT scans obtained 2 months after completion of radiation therapy show patchy consolidation and ground-glass attenuation in the lower lobes (b) and both lung apices (c) conforming to the supraclavicular portals. (d) Chest radiograph obtained 18 months after b and c demonstrates advanced radiation fibrosis in the right lung.
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Figure 7c. Lung changes in a 41-year-old man with adenocarcinoma treated with mediastinal and supraclavicular radiation portals. (a) Pretreatment chest radiograph shows a mass in the right lower lobe as well as right paratracheal lymph nodes (arrow). (b, c) CT scans obtained 2 months after completion of radiation therapy show patchy consolidation and ground-glass attenuation in the lower lobes (b) and both lung apices (c) conforming to the supraclavicular portals. (d) Chest radiograph obtained 18 months after b and c demonstrates advanced radiation fibrosis in the right lung.
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Figure 7d. Lung changes in a 41-year-old man with adenocarcinoma treated with mediastinal and supraclavicular radiation portals. (a) Pretreatment chest radiograph shows a mass in the right lower lobe as well as right paratracheal lymph nodes (arrow). (b, c) CT scans obtained 2 months after completion of radiation therapy show patchy consolidation and ground-glass attenuation in the lower lobes (b) and both lung apices (c) conforming to the supraclavicular portals. (d) Chest radiograph obtained 18 months after b and c demonstrates advanced radiation fibrosis in the right lung.
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Radiation-induced lesions in the lung apices corresponding to the supraclavicular portals may be confused with pulmonary tuberculosis that has been reactivated by irradiation (Fig 8) (2). Visualization of centrilobular nodules or branching linear structures ("tree-in-bud" lesions) at CT may indicate the presence of tuberculosis (18).
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Figure 8a. Pulmonary tuberculosis mimicking radiation pneumonitis in a 47-year-old man with lung cancer in the right middle lobe. (a) Radiograph obtained 4 months after completion of radiation therapy shows ill-defined haziness in the right lung (open arrows) within the radiation portal. Patchy, nodular areas of increased opacity are seen in the left upper lung (arrowheads). (b) CT scan through the carina demonstrates nodular and tree-in-bud lesions (arrowhead) in the left upper lobe and in the superior segment of the left lower lobe, findings that are consistent with tuberculosis. The ground-glass attenuation seen in the right upper lobe (arrows) represents radiation pneumonitis.
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Figure 8b. Pulmonary tuberculosis mimicking radiation pneumonitis in a 47-year-old man with lung cancer in the right middle lobe. (a) Radiograph obtained 4 months after completion of radiation therapy shows ill-defined haziness in the right lung (open arrows) within the radiation portal. Patchy, nodular areas of increased opacity are seen in the left upper lung (arrowheads). (b) CT scan through the carina demonstrates nodular and tree-in-bud lesions (arrowhead) in the left upper lobe and in the superior segment of the left lower lobe, findings that are consistent with tuberculosis. The ground-glass attenuation seen in the right upper lobe (arrows) represents radiation pneumonitis.
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A variety of techniques are used to deliver high-dose radiation to the mediastinum with minimal irradiation of the spinal cord. These include multiple beam arrangements with lateral or oblique portals, rotational therapy, high-energy electrons, and individual posterior blocking of the spinal cord (19). Use of complex portal arrangements may induce pulmonary areas of increased opacity at unusual locations away from the site of disease that may be mistaken for other disease entities (Fig 9). Recognition of such complex arrangements may be facilitated with computed dosimetric reconstruction (20).
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Figure 9a. Radiation pneumonitis in a 60-year-old man with recurrent lung cancer following left lower lobectomy. The unusual location of the disease reflects the use of oblique portals. (a) Localization radiograph shows a right anterior oblique mediastinal portal. A radiation dose of 24 Gy was administered with right anterior and left posterior oblique beam angles after irradiation with 30 Gy in an anteroposterior-posteroanterior direction. (b) Radiograph obtained 4 weeks after completion of radiation therapy shows ill-defined haziness in the upper and middle left lung. (c, d) CT scans obtained through the aortic arch (c) and at the subcarina level (d) at the same time as b demonstrate asymmetric, patchy consolidation anterolaterally in the right lung and posterolaterally in the left lung conforming to the shape of the right anterior and left posterior oblique portals.
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Figure 9b. Radiation pneumonitis in a 60-year-old man with recurrent lung cancer following left lower lobectomy. The unusual location of the disease reflects the use of oblique portals. (a) Localization radiograph shows a right anterior oblique mediastinal portal. A radiation dose of 24 Gy was administered with right anterior and left posterior oblique beam angles after irradiation with 30 Gy in an anteroposterior-posteroanterior direction. (b) Radiograph obtained 4 weeks after completion of radiation therapy shows ill-defined haziness in the upper and middle left lung. (c, d) CT scans obtained through the aortic arch (c) and at the subcarina level (d) at the same time as b demonstrate asymmetric, patchy consolidation anterolaterally in the right lung and posterolaterally in the left lung conforming to the shape of the right anterior and left posterior oblique portals.
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Figure 9c. Radiation pneumonitis in a 60-year-old man with recurrent lung cancer following left lower lobectomy. The unusual location of the disease reflects the use of oblique portals. (a) Localization radiograph shows a right anterior oblique mediastinal portal. A radiation dose of 24 Gy was administered with right anterior and left posterior oblique beam angles after irradiation with 30 Gy in an anteroposterior-posteroanterior direction. (b) Radiograph obtained 4 weeks after completion of radiation therapy shows ill-defined haziness in the upper and middle left lung. (c, d) CT scans obtained through the aortic arch (c) and at the subcarina level (d) at the same time as b demonstrate asymmetric, patchy consolidation anterolaterally in the right lung and posterolaterally in the left lung conforming to the shape of the right anterior and left posterior oblique portals.
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Figure 9d. Radiation pneumonitis in a 60-year-old man with recurrent lung cancer following left lower lobectomy. The unusual location of the disease reflects the use of oblique portals. (a) Localization radiograph shows a right anterior oblique mediastinal portal. A radiation dose of 24 Gy was administered with right anterior and left posterior oblique beam angles after irradiation with 30 Gy in an anteroposterior-posteroanterior direction. (b) Radiograph obtained 4 weeks after completion of radiation therapy shows ill-defined haziness in the upper and middle left lung. (c, d) CT scans obtained through the aortic arch (c) and at the subcarina level (d) at the same time as b demonstrate asymmetric, patchy consolidation anterolaterally in the right lung and posterolaterally in the left lung conforming to the shape of the right anterior and left posterior oblique portals.
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Small Cell Lung Cancer.—Small cell lung cancer is sensitive to many chemotherapeutic agents and is treated with sequential irradiation after the completion of chemotherapy or with concurrent chemotherapy and radiation therapy. Portal arrangements in the irradiation of small cell lung cancer are a subject of controversy. Larger portals include both hilar regions, the entire mediastinum, and both supraclavicular areas. More limited portals include only the primary tumor and adjacent high-risk lymph node areas because chemotherapy can be used to effectively combat subclinical or microscopic disease (1) (Fig 5e, 5f).
Breast Cancer.—Tangential beam radiation portals are frequently used to treat patients with breast cancer. Typically, a 1.5–3-cm strip of underlying peripheral lung is included in the irradiated volume. Radiation pneumonitis or fibrosis occurs at the peripheral lung anterolaterally, has a characteristic shape, and is better visualized at CT than at chest radiography (13,21) (Fig 10). The supraclavicular portal is generally positioned with the inferior border at the first or second intercostal space. When supraclavicular portals are used, radiation-induced change occurs in the apex of the lung; the resulting lesions are similar to those seen in pulmonary tuberculosis (Fig 10). Internal mammary lymph nodes are irradiated with an anteroposterior or oblique beam angle to match the medial tangential beam portal, resulting in paramediastinal lung changes (13) (Fig 11).
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Figure 10a. Right breast cancer in a 56-year-old woman who had undergone local excision and irradiation. (a, b) Portal radiographs demonstrate a tangential beam radiation field (a) and a supraclavicular field (b). (c) Radiograph obtained 3 months after completion of radiation therapy shows ill-defined haziness in the lateral part of the right middle lung (solid arrows) and right apex (open arrows). (d, e) Thin-section CT scans obtained 4 months later demonstrate consolidation with a sharp posterior margin peripherally in the right upper lobe conforming to the shape of the tangential beam radiation portal (d), as well as consolidation and ground-glass attenuation in the right apex conforming to the supraclavicular portal (e).
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Figure 10b. Right breast cancer in a 56-year-old woman who had undergone local excision and irradiation. (a, b) Portal radiographs demonstrate a tangential beam radiation field (a) and a supraclavicular field (b). (c) Radiograph obtained 3 months after completion of radiation therapy shows ill-defined haziness in the lateral part of the right middle lung (solid arrows) and right apex (open arrows). (d, e) Thin-section CT scans obtained 4 months later demonstrate consolidation with a sharp posterior margin peripherally in the right upper lobe conforming to the shape of the tangential beam radiation portal (d), as well as consolidation and ground-glass attenuation in the right apex conforming to the supraclavicular portal (e).
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Figure 10c. Right breast cancer in a 56-year-old woman who had undergone local excision and irradiation. (a, b) Portal radiographs demonstrate a tangential beam radiation field (a) and a supraclavicular field (b). (c) Radiograph obtained 3 months after completion of radiation therapy shows ill-defined haziness in the lateral part of the right middle lung (solid arrows) and right apex (open arrows). (d, e) Thin-section CT scans obtained 4 months later demonstrate consolidation with a sharp posterior margin peripherally in the right upper lobe conforming to the shape of the tangential beam radiation portal (d), as well as consolidation and ground-glass attenuation in the right apex conforming to the supraclavicular portal (e).
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Figure 10d. Right breast cancer in a 56-year-old woman who had undergone local excision and irradiation. (a, b) Portal radiographs demonstrate a tangential beam radiation field (a) and a supraclavicular field (b). (c) Radiograph obtained 3 months after completion of radiation therapy shows ill-defined haziness in the lateral part of the right middle lung (solid arrows) and right apex (open arrows). (d, e) Thin-section CT scans obtained 4 months later demonstrate consolidation with a sharp posterior margin peripherally in the right upper lobe conforming to the shape of the tangential beam radiation portal (d), as well as consolidation and ground-glass attenuation in the right apex conforming to the supraclavicular portal (e).
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Figure 10e. Right breast cancer in a 56-year-old woman who had undergone local excision and irradiation. (a, b) Portal radiographs demonstrate a tangential beam radiation field (a) and a supraclavicular field (b). (c) Radiograph obtained 3 months after completion of radiation therapy shows ill-defined haziness in the lateral part of the right middle lung (solid arrows) and right apex (open arrows). (d, e) Thin-section CT scans obtained 4 months later demonstrate consolidation with a sharp posterior margin peripherally in the right upper lobe conforming to the shape of the tangential beam radiation portal (d), as well as consolidation and ground-glass attenuation in the right apex conforming to the supraclavicular portal (e).
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Figure 11a. Recurrent breast cancer in the chest wall in a 39-year-old woman who had undergone partial mastectomy and axillary dissection. (a) Localization radiograph shows an anteroposterior portal used for internal mammary and chest wall irradiation. (b) Drawing illustrates isodose distribution of chest wall tangential beam and internal mammary radiation fields. (c) Radiograph obtained 6 months after completion of therapy shows chronic radiation-induced change in the left upper lung conforming to the internal mammary field. (d) Thin-section CT scan shows discrete consolidation with chronic fibrotic change in the paramediastinal region of the left upper lobe.
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Figure 11b. Recurrent breast cancer in the chest wall in a 39-year-old woman who had undergone partial mastectomy and axillary dissection. (a) Localization radiograph shows an anteroposterior portal used for internal mammary and chest wall irradiation. (b) Drawing illustrates isodose distribution of chest wall tangential beam and internal mammary radiation fields. (c) Radiograph obtained 6 months after completion of therapy shows chronic radiation-induced change in the left upper lung conforming to the internal mammary field. (d) Thin-section CT scan shows discrete consolidation with chronic fibrotic change in the paramediastinal region of the left upper lobe.
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Figure 11c. Recurrent breast cancer in the chest wall in a 39-year-old woman who had undergone partial mastectomy and axillary dissection. (a) Localization radiograph shows an anteroposterior portal used for internal mammary and chest wall irradiation. (b) Drawing illustrates isodose distribution of chest wall tangential beam and internal mammary radiation fields. (c) Radiograph obtained 6 months after completion of therapy shows chronic radiation-induced change in the left upper lung conforming to the internal mammary field. (d) Thin-section CT scan shows discrete consolidation with chronic fibrotic change in the paramediastinal region of the left upper lobe.
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Figure 11d. Recurrent breast cancer in the chest wall in a 39-year-old woman who had undergone partial mastectomy and axillary dissection. (a) Localization radiograph shows an anteroposterior portal used for internal mammary and chest wall irradiation. (b) Drawing illustrates isodose distribution of chest wall tangential beam and internal mammary radiation fields. (c) Radiograph obtained 6 months after completion of therapy shows chronic radiation-induced change in the left upper lung conforming to the internal mammary field. (d) Thin-section CT scan shows discrete consolidation with chronic fibrotic change in the paramediastinal region of the left upper lobe.
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Esophageal Cancer.—Radiation portals with a 5–6-cm margin above and below the tumor are generally recommended in the treatment of esophageal cancer. Lesions in the upper esophagus are usually treated from the laryngopharynx to the carina with portals that include supraclavicular and superior mediastinal nodes. Lesions in the lower two-thirds of the esophagus are treated with portals that include the entire thoracic esophagus as well as bilateral supraclavicular nodes (22). Radiation-induced change may be difficult to detect at radiography. CT frequently demonstrates radiation-related damage in the lungs adjacent to the mediastinum (Fig 12).
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Figure 12a. Squamous cell carcinoma in the lower esophagus of a 64-year-old man. (a) Esophagogram shows a mass in the lower esophagus (arrows). (b) Portal radiograph shows a narrow mediastinal portal that includes the left supraclavicular area. (c) Radiograph obtained 6 months after completion of therapy shows dense areas of increased opacity in the medial portion of the left lung with volume loss (arrows). (d, e) CT scans obtained at the same time as c demonstrate solid consolidation with a sharp lateral margin (arrows) in the paramediastinal area of the apex (d) and lower lobe of the left lung (e).
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Figure 12b. Squamous cell carcinoma in the lower esophagus of a 64-year-old man. (a) Esophagogram shows a mass in the lower esophagus (arrows). (b) Portal radiograph shows a narrow mediastinal portal that includes the left supraclavicular area. (c) Radiograph obtained 6 months after completion of therapy shows dense areas of increased opacity in the medial portion of the left lung with volume loss (arrows). (d, e) CT scans obtained at the same time as c demonstrate solid consolidation with a sharp lateral margin (arrows) in the paramediastinal area of the apex (d) and lower lobe of the left lung (e).
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Figure 12c. Squamous cell carcinoma in the lower esophagus of a 64-year-old man. (a) Esophagogram shows a mass in the lower esophagus (arrows). (b) Portal radiograph shows a narrow mediastinal portal that includes the left supraclavicular area. (c) Radiograph obtained 6 months after completion of therapy shows dense areas of increased opacity in the medial portion of the left lung with volume loss (arrows). (d, e) CT scans obtained at the same time as c demonstrate solid consolidation with a sharp lateral margin (arrows) in the paramediastinal area of the apex (d) and lower lobe of the left lung (e).
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Figure 12d. Squamous cell carcinoma in the lower esophagus of a 64-year-old man. (a) Esophagogram shows a mass in the lower esophagus (arrows). (b) Portal radiograph shows a narrow mediastinal portal that includes the left supraclavicular area. (c) Radiograph obtained 6 months after completion of therapy shows dense areas of increased opacity in the medial portion of the left lung with volume loss (arrows). (d, e) CT scans obtained at the same time as c demonstrate solid consolidation with a sharp lateral margin (arrows) in the paramediastinal area of the apex (d) and lower lobe of the left lung (e).
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Figure 12e. Squamous cell carcinoma in the lower esophagus of a 64-year-old man. (a) Esophagogram shows a mass in the lower esophagus (arrows). (b) Portal radiograph shows a narrow mediastinal portal that includes the left supraclavicular area. (c) Radiograph obtained 6 months after completion of therapy shows dense areas of increased opacity in the medial portion of the left lung with volume loss (arrows). (d, e) CT scans obtained at the same time as c demonstrate solid consolidation with a sharp lateral margin (arrows) in the paramediastinal area of the apex (d) and lower lobe of the left lung (e).
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Mediastinal Tumors.—The mantle field used for definitive radiation therapy in patients with Hodgkin or non-Hodgkin lymphomas includes all the major lymph node regions above the diaphragm. The field extends from the inferior portion of the mandible nearly to the level of the insertion of the diaphragm. Lung blocks are designed to conform to patient anatomy and tumor distribution (23,24). Radiation pneumonitis varies from minimal to extremely marked change in the paramediastinal areas and in both apices (25) (Figs 13, 14). In patients with Hodgkin or non-Hodgkin lymphoma without mediastinal disease who have undergone chemotherapy, the mediastinal field may be eliminated (supramediastinal mantle [minimantle]) (24).
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Figure 13a. Non-Hodgkin lymphoma in a 20-year-old woman. (a) Portal radiograph shows a mantle field. (b, c) CT scans obtained 6 months after completion of radiation therapy show minimal radiation-induced change with linear, streaky shadows in the paramediastinal regions of the lungs (b) as well as in both apices (c).
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Figure 13b. Non-Hodgkin lymphoma in a 20-year-old woman. (a) Portal radiograph shows a mantle field. (b, c) CT scans obtained 6 months after completion of radiation therapy show minimal radiation-induced change with linear, streaky shadows in the paramediastinal regions of the lungs (b) as well as in both apices (c).
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Figure 13c. Non-Hodgkin lymphoma in a 20-year-old woman. (a) Portal radiograph shows a mantle field. (b, c) CT scans obtained 6 months after completion of radiation therapy show minimal radiation-induced change with linear, streaky shadows in the paramediastinal regions of the lungs (b) as well as in both apices (c).
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Figure 14a. Non-Hodgkin lymphoma in a 35-year-old woman. (a) Radiograph obtained 4 weeks after completion of radiation therapy shows alveolar consolidation in the medial zones of both lungs. Pleural effusion is also seen. A tentative diagnosis of radiation pneumonitis was made, and steroid therapy was initiated. (b) Radiograph obtained 2 months later shows chronic radiation change with fibrosis and volume loss. Note the symmetric bilateral lesion with extension to the apices.
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Figure 14b. Non-Hodgkin lymphoma in a 35-year-old woman. (a) Radiograph obtained 4 weeks after completion of radiation therapy shows alveolar consolidation in the medial zones of both lungs. Pleural effusion is also seen. A tentative diagnosis of radiation pneumonitis was made, and steroid therapy was initiated. (b) Radiograph obtained 2 months later shows chronic radiation change with fibrosis and volume loss. Note the symmetric bilateral lesion with extension to the apices.
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Head and Neck Tumors.—The lung apices are often irradiated incidentally during treatment that is designed to prevent tumor recurrence in the lower neck and supraclavicular fossa; consequently, radiation-induced changes are often encountered in the lung apices in patients who have been treated for head and neck tumors (26).
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Reduced Portal Volumes and Conformal Radiation Therapy
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With the development of conformal radiation therapy, in which the high-dose region conforms to the shape of the target volume in three dimensions while minimizing the dose delivered to normal tissues, the efficacy of traditional portals, target volumes, and beam arrangements has been questioned (1,27). There is a strong trend in radiation therapy toward the use of smaller, involved-field portals (Fig 15) for several reasons: (a) the development of better diagnostic technology such as CT and magnetic resonance imaging that enables better definition of tumor volumes for radiation treatment planning; (b) the development of better radiation therapy hardware and planning software that allows the use of multiple complex radiation fields with unusual beam directions; (c) the recognition of the serious problem of acute and late complications from radiation therapy, which are probably closely related to portal volume; and (d) the development of more effective systemic chemotherapy for controlling microscopic disease (27,28). These issues are particularly relevant in the treatment of lung cancer and lymphomas, which are probably the two cancers in which radiation pneumonitis is most commonly seen.
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Figure 15. Portal used for irradiation of non-small cell lung cancer. Portal radiograph shows an involved-field portal that was used to treat a peripheral tumor with chest wall invasion. Because there was no evidence of lymphadenopathy, the tumor was treated without hilar or mediastinal fields.
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Conclusions
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The shape and distribution of radiation-induced lung disease vary with the radiation methods used to treat thoracic tumors that differ with respect to location, extent, and pathologic features. Knowledge of this variation in radiologic findings will help diagnostic radiologists identify and differentiate abnormalities seen at chest radiography and CT in patients treated with radiation therapy.
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Footnotes
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CME FEATURE This article meets the criteria for 1.0 credit hour in category 1 of the AMA Physician's Recognition Award. To obtain credit, see the questionnaire on pp 244-252.
LEARNING OBJECTIVES After reading this article and taking the test, the reader will be able to:
• Recognize the characteristic imaging features of a variety of radiation-induced lung diseases.
• Be familiar with the technical factors in radiation therapy that may increase the risk of radiation-induced lung disease.
• Be familiar with radiation methods used to treat different thoracic tumors that vary in location, extent, and pathologic diagnosis.
• Understand the relationship between imaging features of various radiation-induced lung diseases and use of different radiation methods.
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References
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Abstract
Introduction
