Wound Trauma Exacerbates Acute, but not Delayed, Effects of Radiation in Rats: Mitigation by Lisinopril.

The goal of this study is to understand and mitigate the effects of wounds on acute radiation syndrome (ARS) and delayed effects of acute radiation exposure (DEARE), for preparedness against a radiological attack or accident. Combined injuries from concomitant trauma and radiation are likely in these scenarios. Either exacerbation or mitigation of radiation damage by wound trauma has been previously reported in preclinical studies. Female WAG/RijCmcr rats received 13 Gy X-rays, with partial-body shielding of one leg. Within 2 h, irradiated rats and non-irradiated controls were given full-thickness skin wounds with or without lisinopril, started orally 7 days after irradiation. Morbidity, skin wound area, breathing interval and blood urea nitrogen were measured up to 160 days post-irradiation to independently evaluate wound trauma and DEARE. Wounding exacerbated morbidity in irradiated rats between 5 and 14 days post-irradiation (during the ARS phase), and irradiation delayed wound healing. Wounding did not alter delayed morbidities from radiation pneumonitis or nephropathy after 30 days post-irradiation. Lisinopril did not mitigate wound healing, but markedly decreased morbidity during DEARE from 31 through 160 days. The results derived from this unique model of combined injuries suggest different molecular mechanisms of injury and healing of ARS and DEARE after radiation exposure.

TGF-ß1 rs1982073 polymorphism contributes to radiation pneumonitis in lung cancer patients: a meta-analysis.

Transforming growth factor beta 1(TGF-ß1) polymorphism was associated with radiation pneumonitis (RP) susceptibility, but their results have been inconsistent. The PubMed and CNKI were searched for case-control studies published up to Januray 01, 2016 was Data were extracted and pooled odds ratios (OR) with 95% confidence intervals (CI) were calculated. In this meta-analysis, we assessed eight publications involving 368 radiation pneumonitis cases and 855 controls of the association between TGF-ß1 T869C (rs1982073) and G915C (rs1800471) polymorphism and RP susceptibility. Our analysis suggested that TGF-ß1 T869C rs1982073 polymorphism was associated with lower RP risk for CT combined CC versus TT model (OR = 0.58, 95% CI = 0.43-0.77). However, for the G915C rs1800471 polymorphism, no association was found between the polymorphism and the susceptibility to RP in GC combined CC versus GG model (OR = 0.82, 95% CI = 0.50-1.35). These results from the meta-analysis suggest that T869C rs1982073 polymorphism of TGF-ß1 may be associated with RP risk, and there may be no association between G915C polymorphism and RP risk.

Correlations Between Serum IL-6 Levels and Radiation Pneumonitis in Lung Cancer Patients: A Meta-Analysis.

OBJECTIVE: Diagnostic significance of interleukin 6 (IL-6) for lung cancer patients with radiation pneumonitis (RP) was examined within various studies, but yielded conflicting results. Thus, this meta-analysis was performed to demonstrate correlations between serum IL-6 levels and RP in lung cancer patients. METHOD: Electronic databases updated to March 2014 were searched to find relevant studies. Relevant literatures were searched under the PubMed, Embase, Web of Science, Cochrane Library, CISCOM, CINAHL, Google Scholar, CBM and CNKI databases. STATA statistical software (Version 12.0, Stata Corporation, and College Station, TX) Standardized mean difference (SMD), and its corresponding 95% confidence intervals (CIs) were used for this meta-analysis. In addition, nine cohort studies met the inclusion criteria and involved a total of 137 RP patients and 295 non-RP patients. RESULTS: The results of combined SMD suggested that serum IL-6 levels in RP patients was significantly higher than in non-RP patients before radiotherapy. While, there was a significant difference in serum IL-6 levels of RP patients between before and after radiotherapy, we observed no difference in serum IL-6 levels between RP patients and non-RP patients after radiotherapy. Ethnicity-stratified analyses indicated that increased serum IL-6 levels were related to the risk of RP in lung cancer patients among Caucasians, but not detected among Asians (all P > 0.05). CONCLUSION: The main finding of our meta-analysis reveals that increased serum IL-6 levels may contribute to the incidence of RP in lung cancer patients, especially among Caucasians.

Radiation-induced morphea - a literature review.

Radiation-induced morphea (RIM) is a rare and under-recognized skin complication of radiotherapy. It is commonly wrongly diagnosed as other dermatological conditions or malignancy because of similar clinical characteristics. This literature review analyses 66 cases that have been reported in the literature since 1989. The clinical appearance often includes pain and disfiguration of affected area, which may influence the patient's quality of life. There is no clear connection between the radiotherapy dose, the fractionation scheme, the use of a boost, age, the presence of other dermatological conditions or other connective tissue diseases and the occurrence of RIM. Its pathogenesis is still unclear, but several theories are proposed to explain this phenomenon. The available data suggest that the abnormally high secretion of some cytokines (interleukin 4, interleukin 5, transforming growth factor) induced by radiation causes an extensive fibrosis after an activation of fibroblasts. Histological confirmation is crucial in distinguishing RIM from similar-looking diseases, such as chronic radiation dermatitis, cancer recurrence, radiation, recall dermatitis, new carcinoma or cellulitis. There is no clear treatment regimen for this condition. Clinical outcome after therapy is often unsatisfactory. The commonly used methods and agents include: topical and systemic steroids, calcineurin inhibitors, systemic immunosuppressants including methotrexate, tacrolimus, heparin, hyaluronidase, phototherapy (UVA, UVA1, UVB, PUVA), systemic antibiotics, imiquimod, mycophenolate mofetil, photophoresis. The differential diagnosis is challenging and requires a multidisciplinary approach to avoid misdiagnosis and to plan appropriate treatment.

Unusual progression and subsequent improvement in cystic lung disease in a child with radiation-induced lung injury.

Radiation-induced lung disease is a known complication of therapeutic lung irradiation, but the features have not been well described in children. We report the clinical, radiologic and histologic features of interstitial lung disease (ILD) in a 4-year-old child who had previously received lung irradiation as part of successful treatment for metastatic Wilms tumor. Her radiologic abnormalities and clinical symptoms developed in an indolent manner. Clinical improvement gradually occurred with corticosteroid therapy. However, the observed radiologic progression from interstitial and reticulonodular opacities to diffuse cystic lung disease, with subsequent improvement, is striking and has not been previously described in children.

Distinguishing immune checkpoint inhibitor-related pneumonitis from radiation pneumonitis by CT radiomics features in non-small cell lung cancer.

PURPOSE: To develop a CT-based model to classify pneumonitis etiology in patients with non-small cell lung cancer(NSCLC) after radiotherapy(RT) and Immune checkpoint inhibitors(ICIs). METHODS: We retrospectively identified 130 NSCLC patients who developed pneumonitis after receipt of ICIs only (n = 50), thoracic RT only (n = 50) (ICIs only + thoracic RT only, the training cohort, n = 100), and RT + ICIs (the test cohort, n = 30). Clinical and CT radiomics features were described and compared between different groups. We constructed a random forest (RF) classifier and a linear discriminant analysis (LDA) classifier by CT radiomics to discern pneumonitis etiology. RESULTS: The patients in RT + ICIs group have more high grade (grade 3-4) pneumonitis compared to patients in ICIs only or RT only group (p < 0.05). Pneumonitis after the combined therapy was not a simple superposition mode of RT-related pneumonitis(RP) and ICI-related pneumonitis(CIP), resulting in the distinct characteristics of both RT and ICIs-related pneumonitis. The RF classifier showed favorable discrimination between RP and CIP with an area under the receiver operating curve (AUC) of 0.859 (95 %CI: 0.788-0.929) in the training cohort and 0.851 (95 % CI: 0.700-1) in the test cohort. The LDA classifier achieved an AUC of 0.881 (95 %CI: 0.815-0.947) in the training cohort and 0.842 (95 %CI: 0.686-0.997) in the test cohort. Our analysis revealed four principal CT-based features shared across both models:original_glrlm_LongRunLowGrayLevelEmphasis, wavelet-HLL_firstorder_Median, wavelet-LLL_ngtdm_Busyness， and wavelet-LLL_glcm_JointAverage. CONCLUSION: CT radiomics-based classifiers could provide a noninvasive method to identify the predominant etiology in NSCLC patients who developed pneumonitis after RT alone, ICIs alone or RT + ICIs.

[Impact of diabetes mellitus on clinicopathological factors and relation with radiation pneumonitis in 332 patients with lung cancer].

OBJECTIVE: To explore the relation between diabetes mellitus and clinicopathological factors and the incidence of radiation pneumonitis in patients with non-small cell lung cancer. METHODS: The data of 332 patients with non-small cell lung cancer, who were admitted to the Department of Oncology of Third Xiangya Hospital of Central South University between January 2007 and August 2009, were collected retrospectively. The patients were divided into a diabetes mellitus (DM) group (n=45) and a non-diabetes mellitus (NDM) group (n=287). The clinicopathological factors were compared between the two groups. The patients who received radiotherapy were further divided into a diabetes mellitus (DMR) group (n=33) and a non-diabetes mellitus group (NDMR) group(n=287), and the incidence of radiation pneumonitis was compared. RESULTS: A total of 45 patients (13.55%)developed diabetes mellitus. There was significant difference in the body-weight, age and hypertension (P<0.05), while no significant difference in the pathologic factors, such as tumor pathological type, degree of differentiation, and classification of malignant tumors (TNM) stage between the two groups(P>0.05). No significant difference in the irradiation area was found between the DM group and the NDM group(P>0.05). The incidence of radiation pneumonitis in the DMR group was 42.42%(14 out of 33), while 21.31%(39 out of 183) in the NDMR group, with significant difference in the incidence of radiation pneumonitis between the DMR group and the NDMR group(P<0.05). The risk value in the DMR group was 2.721 folds (95%CI, 1.253-5.910) that in the NDMR group in patients with non-small cell lung cancer companied with diabetes mellitus. CONCLUSION: Diabetes mellitus is the risk factor of radiation pneumonitis for patients with nonsmall cell lung cancer who receive radiotherapy.

Hemoptysis due to breath-hold diving following chemotherapy and lung irradiation.

Breath-hold diving, also known as free-diving, describes the practice of intentional immersion under water without an external supply of oxygen. Pulmonary hemorrhage with hemoptysis has been reported as a complication of immersion and breath-hold diving in young healthy athletes. We report the case of a 60-year-old man with a history of radiation and chemotherapy for breast carcinoma, who developed the abrupt onset of hemoptysis in the setting of swimming and breath-hold diving. A computed tomography (CT) scan of the chest demonstrated an area of ground glass opacification, suggestive of pulmonary hemorrhage, superimposed on a background of reticular opacities within the prior radiation field. A follow-up CT scan of the chest, obtained 2 months after presentation, demonstrated resolution of the ground glass opacification, but persistence of fibrotic features attributable to prior radiation therapy. We postulate that prior irradiation of the chest resulted in lung injury and fibrosis which, in turn, rendered the affected region of the lung susceptible to "stress failure," due to an increase in the transcapillary pressure gradient arising from immersion and breath-hold diving. Patients with a history of lung injury resulting from chest irradiation should be cautioned about pulmonary hemorrhage and hemoptysis as a potential complication of swimming and breath-hold diving.

Pulmonary Nocardiosis Caused by Nocardia exalbida in a Patient with Lung Cancer and Radiation Pneumonitis: A Case Report and Literature Review.

We report a case of Nocardia exalbida (N.exalbida)-induced pneumonia in a 70-year old Japanese man with lung cancer and radiation pneumonitis. He initially received doripenem (1.5 g/day) for pneumonia treatment, and N.exalbida was identified by a clone library analysis of bronchoalveolar lavage fluid obtained from the pneumonia lesion. The doripenem dosage was therefore increased to 3.0 g/day with adjunctive trimethoprim/sulfamethoxazole, and his pneumonia improved. N. exalbida is susceptible to antibiotics; thus, in nocardiosis, N. exalbida infection might be associated with a good response to treatment, although its clinical findings are non-specific and similar to those of other Nocardia infections.

Cardiac Remodeling and Reversible Pulmonary Hypertension During Pneumonitis in Rats after 13-Gy Partial-Body Irradiation with Minimal Bone Marrow Sparing: Effect of Lisinopril.

Total-body irradiation causes acute and delayed toxicity to hematopoietic, pulmonary, cardiac, gastrointestinal, renal, and other organ systems. Angiotensin-converting enzyme inhibitors mitigate many of the delayed injuries to these systems. The purpose of this study was to define echocardiographic features in rats at two times after irradiation, the first before lethal radiation pneumonitis (50 d) and the second after recovery from pneumonitis but before lethal radiation nephropathy (100 d), and to determine the actions of the angiotensin-converting enzyme inhibitor lisinopril. Four groups of female WAG/RijCmcr rats at 11-12 wk of age were studied: nonirradiated, nonirradiated plus lisinopril, 13-Gy partial-body irradiation sparing one hind leg (leg-out partial-body irradiation), and 13-Gy leg-out partial-body irradiation plus lisinopril. Lisinopril was started 7 d after radiation. Echocardiograms were obtained at 50 and 100 d, and cardiac histology was assessed after 100 d. Irradiation without lisinopril demonstrated echocardiographic transient pulmonary hypertension by 50 d which was largely resolved by 100 d in survivors. Irradiated rats given lisinopril showed no increase in pulmonary artery pressures at 50 d but exhibited left ventricular remodeling. By 100 d these rats showed some signs of pulmonary hypertension. Lisinopril alone had no impact on echocardiographic end points at either time point in nonirradiated rats. Mild increases in mast cells and fibrosis in the heart were observed after 100 d following 13-Gy leg-out partial-body irradiation. These data demonstrate irradiation-induced pulmonary hypertension which was reversed in survivors of pneumonitis. Lisinopril modified cardiovascular remodeling to enhance survival in this model from 41% to 86% (p = 0.0013).

Immune Checkpoint Inhibitor Outcomes for Patients With Non-Small-Cell Lung Cancer Receiving Baseline Corticosteroids for Palliative Versus Nonpalliative Indications.

PURPOSE: Baseline use of corticosteroids is associated with poor outcomes in patients with non-small-cell lung cancer (NSCLC) treated with programmed cell death-1 axis inhibition. To approach the question of causation versus correlation for this association, we examined outcomes in patients treated with immunotherapy depending on whether corticosteroids were administered for cancer-related palliative reasons or cancer-unrelated indications. PATIENTS AND METHODS: Clinical outcomes in patients with NSCLC treated with immunotherapy who received ≥ 10 mg prednisone were compared with outcomes in patients who received 0 to < 10 mg of prednisone. RESULTS: Of 650 patients, the 93 patients (14.3%) who received ≥ 10 mg of prednisone at the time of immunotherapy initiation had shorter median progression-free survival (mPFS) and median overall survival (mOS) times than patients who received 0 to < 10 mg of prednisone (mPFS, 2.0 v 3.4 months, respectively; P = .01; mOS, 4.9 v 11.2 months, respectively; P < .001). When analyzed by reason for corticosteroid administration, mPFS and mOS were significantly shorter only among patients who received ≥ 10 mg prednisone for palliative indications compared with patients who received ≥ 10 mg prednisone for cancer-unrelated reasons and with patients receiving 0 to < 10 mg of prednisone (mPFS, 1.4 v 4.6 v 3.4 months, respectively; log-rank P < .001 across the three groups; mOS, 2.2 v 10.7 v 11.2 months, respectively; log-rank P < .001 across the three groups). There was no significant difference in mPFS or mOS in patients receiving ≥ 10 mg of prednisone for cancer-unrelated indications compared with patients receiving 0 to < 10 mg of prednisone. CONCLUSION: Although patients with NSCLC treated with ≥ 10 mg of prednisone at the time of immunotherapy initiation have worse outcomes than patients who received 0 to < 10 mg of prednisone, this difference seems to be driven by a poor-prognosis subgroup of patients who receive corticosteroids for palliative indications.

Combined photon and electron three-dimensional conformal versus intensity-modulated radiotherapy with integrated boost for adjuvant treatment of malignant pleural mesothelioma after pleuropneumonectomy.

PURPOSE: The optimal technique for postoperative radiotherapy (RT) after extrapleural pleuropneumonectomy (EPP) of malignant pleural mesothelioma (MPM) remains debated. METHODS AND MATERIALS: The data from 8 right-sided and 9 left-sided consecutive cases of MPM treated with RT after radical EPP were reviewed. Of the 17 patients, 8 had been treated with three-dimensional (3D) conformal RT (3D-CRT) and 9 with intensity-modulated RT (IMRT) with 6-MV photons. The clinical outcome and adverse events were assessed. For comparative planning, each case was replanned with 3D-CRT using photons and electrons or with IMRT. Homogeneity, doses to the organs at risk, and target volume coverage were analyzed. RESULTS: Both techniques yielded acceptable plans. The dose coverage and homogeneity of IMRT increased by 7.7% for the first planning target volume and 9.7% for the second planning target volume, ensuring >or=95% of the prescribed dose compared with 3D-CRT (p < 0.01). Compared with 3D-CRT, IMRT increased the dose to the contralateral lung, with an increase in the mean lung dose of 7.8 Gy and an increase in the volume receiving 13 Gy and 20 Gy by 20.5% and 7.2%, respectively (p < 0.01). A negligible dose increase to the contralateral kidney and liver was observed. No differences were seen for the spinal cord and ipsilateral kidney. Two adverse events of clinical relevant lung toxicity were observed with IMRT. CONCLUSION: Intensity-modulated RT and 3D-CRT are both suitable for adjuvant RT. IMRT improves the planning target volume coverage but delivered greater doses to the organs at risk. Rigid dose constraints for the lung should be respected.

Correlation of Radiation Pneumonitis History Before Nivolumab with Onset of Interstitial Lung Disease and Progression-free Survival of Patients with Pre-treated Advanced Non-small Cell Lung Cancer.

BACKGROUND/AIM: Nivolumab has a promising efficacy for patients with non-small-cell lung cancer (NSCLC) as second-line or later treatment, and after radiotherapy as abscopal effect. However, the effects of radiation pneumonitis history before nivolumab have not been clarified. Therefore, we retrospectively analyzed the correlation of a history of radiation pneumonitis before nivolumab with onset of interstitial lung disease (ILD) and progression-free survival (PFS) after nivolumab treatment in patients with previously treated NSCLC. PATIENTS AND METHODS: A total of 201 patients treated with nivolumab were retrospectively reviewed. We collected clinical data of patients at the time of starting nivolumab and we evaluated ILD incidence and PFS in relation to patient characteristics, including radiation pneumonitis history. RESULTS: The median age was 68 years; 135 patients were men, 157 had a smoking history, and 153 had performance status of 0 or 1. Thirty-four patients experienced radiation pneumonitis before nivolumab, and 50 patients received radiotherapy to the chest (31 patients received curative radiotherapy). The overall median PFS was 2.8 months and the overall ILD rate was 12.4%. Higher ILD incidence was observed in the group with a history of radiation pneumonitis (26.5%) compared to the group without radiation pneumonitis (9.6%). The median PFS was 3.6 and 2.3 months, respectively. On multivariate analysis, a history of radiation pneumonitis was also significantly correlated with good PFS (p=0.023). CONCLUSION: Although increasing the risk of ILD, a history of radiation pneumonitis before nivolumab also contributes to the prolongation of PFS after nivolumab.

Stereotactic body radiotherapy (SBRT) for medically inoperable lung metastases-A pooled analysis of the German working group "stereotactic radiotherapy".

OBJECTIVES: The current literature on stereotactic body radiotherapy (SBRT) for oligometastatic disease is characterized by small patient cohorts with heterogeneous primary tumors, metastases location and dose regimes. Hence, this study established a multi-institutional database of 700 patients treated with SBRT for pulmonary metastases to identify prognostic factors influencing survival and local control. MATERIALS AND METHODS: All German radiotherapy departments were contacted and invited to participate in this analysis. A total number of 700 patients with medically inoperable lung metastases treated with SBRT in 20 centers between 1997 and 2014 were included in a database. Primary and metastatic tumor characteristics, treatment characteristics and follow-up data including survival, local control, distant metastases, and toxicity were evaluated. Lung metastases were treated with median PTV-encompassing single doses of 12.5Gy (range 3.0-33.0Gy) in a median number of 3 fractions (range 1-13). RESULTS: After a median follow-up time of 14.3 months, 2-year local control (LC) and overall survival (OS) were 81.2% and 54.4%, respectively. In multivariate analysis, OS was most significantly influenced by pretreatment performance status, maximum metastasis diameter, primary tumor histology, time interval between primary tumor diagnosis and SBRT treatment and number of metastases. For LC, independent prognostic factors were pretreatment performance status, biological effective dose (BED) at PTV isocenter (BEDISO) and single fraction (PTV-encompassing) dose in multivariate analysis. Radiation-induced pneumonitis grade 2 or higher was observed in 6.5% of patients. The only factor significantly influencing toxicity was BEDISO (p=0.006). CONCLUSION: SBRT for medically inoperable patients with pulmonary metastases achieved excellent local control and promising overall survival. Important prognostic factors were identified for selecting patients who might benefit most from this therapy approach.

Truncated Plasminogen Activator Inhibitor-1 Protein Protects From Pulmonary Fibrosis Mediated by Irradiation in a Murine Model.

PURPOSE: To determine whether the delivery of recombinant truncated plasminogen activator inhibitor-1 (PAI-1) protein (rPAI-1(23)) would protect from the development of radiation-induced lung injury. METHODS AND MATERIALS: C57Bl/6 mice received intraperitoneal injections of rPAI-1(23) (5.4 µg/kg/d) or vehicle for 18 weeks, beginning 2 days before irradiation (IR) (5 daily fractions of 6 Gy). Cohorts of mice were followed for survival (n=8 per treatment) and tissue collection (n=3 per treatment and time point). Fibrosis in lung was assessed with Masson-Trichrome staining and measurement of hydroxyproline content. Senescence was assessed with staining for ß-galactosidase activity in lung and primary pneumocytes. RESULTS: Hydroxyproline content in irradiated lung was significantly reduced in mice that received rPAI-1(23) compared with mice that received vehicle (IR+vehicle: 84.97 µg/lung; IR+rPAI-1(23): 56.2 µg/lung, P=.001). C57Bl/6 mice exposed to IR+vehicle had dense foci of subpleural fibrosis at 19 weeks, whereas the lungs of mice exposed to IR+rPAI-1(23) were largely devoid of fibrotic foci. Cellular senescence was significantly decreased by rPAI-1(23) treatment in primary pneumocyte cultures and in lung at multiple time points after IR. CONCLUSIONS: These studies identify that rPAI-1(23) is capable of preventing radiation-induced fibrosis in murine lungs. These antifibrotic effects are associated with increased fibrin metabolism, enhanced matrix metalloproteinase-3 expression, and reduced senescence in type 2 pneumocytes. Thus, rPAI-1(23) is a novel therapeutic option for radiation-induced fibrosis.

Challenges in defining radiation pneumonitis in patients with lung cancer.

PURPOSE: To assess the difficulty of assigning a definitive clinical diagnosis of radiation (RT)-induced lung injury in patients irradiated for lung cancer. METHODS: Between 1991 and 2003, 318 patients were enrolled in a prospective study to evaluate RT-induced lung injury. Only patients with lung cancer who had a longer than 6-month follow-up (251 patients) were considered in the current analysis. Of these, 47 of 251 patients had Grade >/=2 (treated with steroids) increasing shortness of breath after RT, thought possibly consistent with pneumonitis/fibrosis. The treating physician, and one to three additional reviewing physicians, evaluated the patients or their medical records, or both. The presence or absence of confounding clinical factors that made the diagnosis of RT-induced uncertain lung injury were recorded. RESULTS: Thirty-one of 47 patients (66%) with shortness of breath had "classic" pneumonitis, i.e., they responded to steroids and had a definitive diagnosis of pneumonitis. In 13 of 47 patients (28%), the diagnosis of RT-induced toxicity was confounded by possible infection; exacerbation of preexisting lung disease (chronic obstructive pulmonary disease); tumor regrowth/progression; and cardiac disease in 6, 8, 5, and 1 patients, respectively (some of the patients had multiple confounding factors and were counted more than once). An additional 3 patients (6%) had progressive shortness of breath and an overall clinical course more consistent with fibrosis. All 3 had evidence of bronchial stenosis by bronchoscopy. CONCLUSIONS: Scoring of radiation pneumonitis was challenging in 28% of patients treated for lung cancer owing to confounding medical conditions. Recognition of this uncertainty is needed and may limit our ability to understand RT-induced lung injury.

Radiation-induced organizing pneumonia after stereotactic body radiotherapy for lung tumor.

The aim of this retrospective study was to investigate characteristics of organizing pneumonia (OP) after stereotactic body radiotherapy (SBRT) for lung tumor. Between September 2010 and June 2014, patients who were diagnosed as Stage I lung cancer and treated with SBRT at our institution were included in this study. A total of 78 patients (47 males with a median age of 80 years) were analyzed. The median follow-up period was 23 months. Five patients (6.4%) developed OP at 6-18 months after SBRT. The cumulative incidence of OP was 4.3% (95% confidence interval [CI], 1.1-11.0) and 8.2% (95% CI, 2.9-17.0) at 1 and 2 years, respectively. Tumor location (superior and middle lobe vs inferior lobe) was shown to be a borderline significant factor for the occurrence of OP ( P: = 0.069). In the subgroup analysis of patients with a radiographic follow-up period at least 6 months, or who died within 6 months after SBRT, 7 of 72 patients (9.7%) developed Grade 2 or 3 radiation pneumonitis (G2/3 RP) at 2-4 months after SBRT. A statistically significant association between G2/3 RP in the subacute phase and OP was shown ( P: = 0.040). In two of the five patients who developed OP, the symptoms and radiographic change were improved rapidly by corticosteroid administration. One patient had relapsed OP after suspending the treatment and re-administration was required. Three patients with minor symptoms were managed without corticosteroid administration and OP resolved without any relapse. The radiation-induced OP should be considered as one of the late lung injuries after SBRT for lung tumors.