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* From the Department of Biomedical Sciences and Human Oncology (Drs. Rolla, Colagrande, Dutto, Chiavassa, and Bucca), the Radiotherapy Division (Drs. Ricardi and Nassisi), University of Torino, Torino, Italy.
Correspondence to: Caterina Bucca, MD, Associate Professor in Clinical Pathophysiology, Department of Biomedical Sciences and Human Oncology, University of Torino, Via Genova 3, 10126 Torino, Italy
| Abstract |
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Design: Follow-up of the changes in lung function and methacholine responsiveness in patients 1, 6, 12, and 24 months after they underwent MRT.
Patients: Thirteen nonasthmatic patients with bulky Hodgkins lymphoma who were scheduled for MRT.
Measurements and results: Chest radiographs, lung function tests, methacholine thresholds of the bronchi (the provocative dose of methacholine causing a 10% fall in FEV1 [PD10]) and central airway (the provocative dose of methacholine causing a 25% fall in the maximal mid-inspiratory flow [PD25MIF50]), and the provocative dose of methacholine causing five or more coughs (PDcough) were serially assessed. One month after patients underwent MRT, there were significant decreases in PD10 (mean [± SEM], 2,583 ± 414 µg to 1,512 ± 422 µg, respectively; p < 0.05), PD25MIF50 (mean 2,898 ± 372 µg to 1,340 ± 356 µg, respectively; p < 0.05), and PDcough (mean 3,127 ± 415 µg to 1,751 ± 447 µg; p < 0.05), which were independent of the decrease in FEV1 and reversed within 6 months in all patients but three. Six months after undergoing MRT, four patients showed radiation-induced lung injury (RI) on chest radiographs, which subsequently evolved into fibrosis. These patients had greater decreases in vital capacity, FEV1, MIF50, and methacholine thresholds than those without RI, and this persisted up to 2 years after they had undergone MRT. One year after the patients underwent MRT, a close relationship was found overall between the change in FEV1 and those in both PD10 (r = 0.733; p = 0.004) and PD25MIF50 (r = 0.712; p = 0.006).
Conclusions: MRT triggers an early transient increase in airway responsiveness, which reverses spontaneously. In patients with RI, the persistence of airway dysfunction long after undergoing MRT may depend on airway remodeling from radiation fibrosis.
Key Words: airway responsiveness mantle radiotherapy radiation-induced cough radiation-induced inflammation radiation-induced lung injury
| Introduction |
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The purpose of this study was to evaluate the early and late changes in nonspecific airway responsiveness in patients after they underwent MRT in relation to symptoms, lung function changes, and evidence of radiation-induced lung injury (RI).
| Materials and Methods |
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The criteria for inclusion in the study were the following: (1) normal results of lung function tests; (2) no respiratory infections in the preceding 2 months; (3) no history of cardiac or bronchopulmonary disease prior to the diagnosis of Hodgkins lymphoma; and (4) no pulmonary complications following treatment with doxorubicin, bleomycin, vinblastine, and dacarbazine.
Study Protocol
The protocol of the study was approved by the institutional
ethics committee, and appropriate informed consent was obtained fromthe
subjects. The patients were examined before the start of MRT and 1, 6,
12, and 24 months after the end of MRT. At each visit, the patients
underwent the following procedures: clinical examination; lung function
tests; tests of lung diffusing capacity; arterial blood gas analysis;
methacholine inhalation challenge; venipuncture for CBC counts and
measurement of some serum markers of lung injury; and chest radiograph.
A CT scan was performed before the patients underwent MRT and 6, 12,
and 24 months after MRT.
RI was diagnosed in patients if a chest radiograph that was performed in the first 6 months after they had undergone MRT showed diffuse haziness or fuzziness within or outside the radiation fields that was not attributable to other pathologic processes and subsequently evolved into linear or patchy densities that were consistent with fibrosis,15 and/or if a lung CT scan showed areas of attenuation that evolved into soft-tissue density changes that were consistent with fibrosis.16 Radiation pneumonitis was diagnosed if radiographic and CT scan abnormalities were associated with symptoms (fever, dyspnea, and cough).17
Lung Function Tests: The measurements were performed following the European Respiratory Society criteria,18 using a computerized water-sealed spirometer connected to helium and carbon monoxide analyzers (BAIRES, with revo and dimo modules; Biomedin; Padua, Italy). The following parameters were measured: (1) static lung volumes (vital capacity [VC], residual volume [by the helium dilution technique in closed circuit], and total lung capacity [TLC]); (2) FEV1, as an index of total airway patency, forced inspiratory volume in 1 s, and maximal mid-inspiratory flow (MIF50) as indexes of the central airway (larynx and extrathoracic or intrathoracic trachea) patency; and (3) transfer factor for carbon monoxide (KCO), by the single-breath method.19 Reference values were obtained from Quanjer.18
Arterial Blood Gas Analysis: PO2 and PCO2 were measured by a blood gas analyzer (ABL 330; Radiometer; Copenhagen, Denmark).
Methacholine Airway Responsiveness:
The assessment of
methacholine airway responsiveness followed a slightly modified
standard method.20
A freshly prepared solution of 1%
methacholine chloride (Lofarma; Milan, Italy) was delivered by a
compressed air nebulizer that was controlled by a breath-actuated
dosimeter (MEFAR MB3; Markos; Monza, Italy). The dosimeter was set to
nebulize for 1 s (output, 0.01 mL/breath); the mass median
diameter of particles was 1.69 µm (geometric SD, 3.3). Methacholine
was inhaled from a mouthpiece connected to the nebulizer in doubling
doses that were obtained by increasing the number of VC breaths from
100 to 3,200 µg. Two minutes after each dose step, three flow-volume
loops were recorded 1 min apart to avoid the effect of deep inhalation.
The interval between doses was about 5 min. FEV1
was used as an index of bronchial narrowing.
MIF50 was arbitrarily used as an index of central
airway (larynx and/or extrathoracic and intrathoracic trachea)
narrowing, since previously we had found that this test nicely reflects
the changes in upper airway patency during bronchial
challenge.21
Coughs were counted at each dose step to
calculate the cough threshold.22
The challenge was stopped
when a 20% fall in FEV1 from baseline was
obtained or when the highest methacholine dose had been reached.
Bronchial and central airway thresholds were computed by plotting the
methacholine dose against the relative percentage drops in
FEV1 and MIF50. The
bronchial threshold was calculated as the provocative dose of
methacholine causing a 10% fall in FEV1
(PD10) from baseline. The choice of using
PD10 to calculate the bronchial threshold instead
of the provocative dose of methacholine causing a 20% fall in
FEV1 (PD20) was made to
limit the need for extrapolation from the data points, since subjects
were not expected to be hyperresponsive before undergoing MRT. However,
the diagnosis of bronchial hyperresponsiveness was based on the classic
criterion of a PD20
800 µg.20
The central airway threshold was expressed arbitrarily as the
provocative dose of methacholine causing a 25% fall in
MIF50
(PD25MIF50),21
and the cough threshold was expressed as the provocative dose causing
five or more coughs (PDcough).22
Central airway and cough
hyperresponsiveness were diagnosed if
PD25MIF50 and PDcough were
800 µg.
Serum Markers of Tissue Injury: Serum lactate dehydrogenase (sLDH), C-reactive protein, and serum angiotensin-converting enzyme activity (sACE) were used as markers of lung injury.23 24 25 A decrease in sACE was considered to be indicative of endothelial injury,25 and a rise was considered to be indicative of macrophage activation.26
MRT Technique: MRT was performed following the technique proposed by Carmel and Kaplan.27 The standard mantle field included cervical, supraclavicular, infraclavicular, axillary, mediastinal, and hilar lymph node-bearing regions. Customized Cerrobend blocks (Multimedica; Genoa, Italy) were used to shield the healthy lung parenchyma, heart, cervical spinal cord, humoral heads, and larynx. The dose of radiation to the mantle field was 36 to 40 Gy administered in 1.8-Gy fractions. Doses given to the mantle fields were weighted 1:1, anterior to posterior, and both anterior and posterior fields were treated daily. With standard mantle blocks, the underlying lung parenchyma received a maximum of 5 to 10% of the specified dose at the central axis due to transmission and scatter.
Statistical Analysis
The changes in the results of lung function tests,
KCO, blood gas analyses, methacholine thresholds, and
levels of serum markers of lung injury that were observed before
patients underwent MRT and 1, 6, 12, and 24 months following MRT
were analyzed using analysis of variance for repeated
measures and the Tukey-Kramer multiple comparisons test. The
relationships among the changes of lung function tests and those of the
methacholine thresholds were evaluated by linear regression analysis. A
p value < 0.05 was considered statistically significant.
| Results |
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The mean (± SEM) values for the results of lung function tests, blood gas analyses, methacholine responsiveness tests, WBC counts, and measurements of serum markers of lung injury before patients undergoing MRT and 1, 6, 12, and 24 months following MRT of the 13 patients who completed the study are reported in Table 1 .
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After MRT
Lung Function Tests: Overall, there was a small but
significant decrease in TLC 1 month after patients underwent MRT, which
persisted until the end of the study. VC levels significantly decreased
only 1 month after MRT. FEV1 levels, airflow
rates, and arterial blood gas levels showed no significant change
throughout the study. There was a small progressive decrease in the
KCO up to 6 months after MRT, and then it improved.
Methacholine Airway Responsiveness: All the methacholine thresholds showed a significant decrease 1 month after MRT, particularly in the PD25MIF50, which in eight patients (62%) was consistent with central airway hyperresponsiveness. Six patients (46%) had bronchial hyperresponsiveness, and seven patients (54%) had cough hyperresponsiveness. As shown in Figure 1 , the changes in PD10 and PD25MIF50 levels were not related to the changes in FEV1 levels. The decrease in methacholine thresholds rapidly recovered, so that, 6 months after MRT, the mean values of PD10, PD25MIF50, and PDcough were only slightly, and not significantly, lower than those before treatment. However, three patients showed persistent airway and cough hyperresponsiveness up to the end of the study. As shown in Figure 1 , 1 year after the patients underwent MRT, the changes in PD10 and PD25MIF50 levels were closely and directly related to the changes in FEV1 levels.
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Markers of Radiation Injury: As shown in Table 1 , the only significant changes were a transient decrease in WBC count and sACE activity 1 month after MRT. Four patients showed a brisk increase in sACE levels 1 year after undergoing MRT. sLDH and C-reactive protein levels remained in the normal range during the entire study.
Lung Imaging: No further relapse of Hodgkins disease was observed during 2 years of follow-up. Six months after undergoing MRT, four patients (31%) presented parenchymal infiltrates that were consistent with RI. The lesions were limited to the radiation fields in two patients, were at the apex of the right lower lobe in one patient, and were in the left lower lobe in one patient, a condition that subsequently evolved into patchy densities that were consistent with fibrosis.
Three of the patients with RI had persistent cough and airway dysfunction, but none displayed the classic radiation pneumonitis syndrome. No significant differences were found between patients with and without RI before they underwent MRT, including smoking history (only one of the four RI patients was a smoker). By contrast, after MRT, patients with RI had persistent and significantly greater decreases in VC, FEV1, MIF50, and methacholine threshold levels (Fig 2 ). The decrease in PD10, PD25MIF50, and PDcough levels showed the following dual trend: an early decrease 1 month after MRT, and a second decrease after 1 year, which was associated with a brisk increase in sACE and fibrotic evolution of radiographic lesions.
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| Discussion |
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The increase in airway responsiveness observed 1 month after MRT could hardly be attributed to lung inflammatory changes caused by Hodgkins lymphoma. In fact, before MRT, airway responsiveness was in the normal range in all the patients but one, and its increase after treatment was never associated with lymphoma relapse.
None of the patients showed clinical evidence of radiation pneumonitis shortly after undergoing MRT. In fact, although five patients complained of cough, none had fever, dyspnea, leukocytosis, radiographic abnormalities, or increases in levels of serum markers of lung injury. There were, rather, significant decreases in WBC counts, due to the combined effect of chemotherapy and radiotherapy, and in sACE levels, which probably are the expression of endothelial injury.25 In 9 of the 13 patients, the possibility that airway dysfunction was the consequence of radiation pneumonitis seems very unlikely. In fact, in these patients no radiographic abnormalities appeared throughout the follow-up, and the PD10, PD25MIF50, and PDcough levels recovered to pretreatment values within 6 months, just at the time when radiation pneumonitis would have become clinically apparent.28 29 In these patients, we may suppose that airway and cough hyperresponsiveness were sustained by transient radiation-induced airway inflammation,6 7 8 9 10 11 which caused epithelial cell damage with an increased mucosal permeability of irritants and an increased sensitivity of the submucosal receptors. The reduction of cough and airway hyperresponsiveness that was observed 6 months after the patients underwent MRT might, thus, depend on the resolution of the inflammatory process with its consequent repair of the epithelium, since bronchial epithelial cells have an estimated doubling time of 1 to 3 weeks.30
By contrast, RI might well have occurred in the four patients who developed typical abnormalities on chest radiographs and CT scans that were performed 6 months after they underwent MRT. According to Morgan et al,31 these abnormalities could be defined in two patients as classic pneumonitis, which is confined to the radiation field, and in the other two patients as sporadic pneumonitis, which is outside the radiation field. Airway dysfunction in these four patients might have been an early sign of ongoing RI. As shown in Figure 2 , these four patients, compared with those without RI, had significantly greater decreases in VC, FEV1 levels, MIF50 levels, and methacholine thresholds throughout the follow-up, and three patients had persistent cough and airway hyperresponsiveness. Interestingly, the methacholine thresholds of the patients with RI showed a dual trend, with an early decrease at 1 month, a transient improvement at 6 months, and a second worsening at 1 year. The latter was associated with radiographic signs of fibrosis and with a brisk increase in sACE levels. We may suppose that the increase in sACE levels was the expression of macrophage activation,26 which contributed to the fibrotic process.32 33 The close relationship between the decreases in both PD10 and PD25MIF50 levels and the decreases in FEV1 that was found in all patients 1 year after they had undergone MRT, but that was not found 1 month after they had undergone MRT, suggests that persistent increases in airway responsiveness long after MRT may be sustained by airway remodeling that is the consequence of radiation fibrosis.
The relatively high incidence of RI found in our series (31%) was probably the consequence of combined chemotherapy and radiotherapy.34 Despite the high incidence of RI, its physiologic consequences were rather mild, and no patient had the classic radiation pneumonitis syndrome. In three of the four patients with RI, the only symptom that ensued after they had undergone MRT was persistent cough, which did not require any treatment. Actually, MRT is not likely to produce significant symptoms or damage, since its radiation field involves only a small volume of the upper lung zones, where both ventilation and perfusion are lowest.29 No predictor of the development of radiation pneumonitis could be found from the comparison between patients with and without RI. However, due to the selection criteria, all the patients had a negative history for bronchopulmonary disease, had normal results of baseline lung function tests, had the same lymphoma stage and extension, and had received the same chemotherapeutic regimen and the same total and fractional radiation dose.
| Conclusions |
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These findings suggest that the assessment of airway responsiveness is much more sensitive than lung function tests, chest radiographs, and serum markers of lung injury in the early detection of radiation-induced airway inflammation. An increase in airway responsiveness, early after treatment, may account for the occurrence of symptoms of airway irritation, such as cough, in patients without overt radiation pneumonitis. While medications such as steroids are known to be useful in treating airway hyperresponsiveness in patients with asthma, further investigation is needed to assess whether topical corticosteroids may improve airway dysfunction and prevent late radiation-induced airway remodeling.
| Acknowledgements |
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| Footnotes |
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Supported by a grant from the Italian Ministry of University and Scientific Research.
Received for publication July 29, 1999. Accepted for publication January 25, 2000.
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