INTRODUCTION: Stereotactic body radiation (SBRT) is an emerging tool in radiation oncology that allows for the minimization of normal tissue volume exposed to high radiation dose as well as the escalation of fractional dose delivery. Few pulmonary complications have been reported. Hypersenstivity Pneumonitis is a rare form of Radiation injury reported with conventional but not stereotactic radiation therapy.
CASE PRESENTATION: A 64-year-old lady with COPD on two litres home Oxygen and a recently diagnosed poorly differentiated squamous cell carcinoma stage T2a N0M0, presented with exertional dyspnea and dry cough, 3 weeks after completion of Stereotactic body radiation treatment with a total of 60 Greys. She was treated as out-patient with 2 courses of Levofloxacin, without any relief. She did not have fever, orthopnea, chest pain, change in appetite or weight loss. She had no history of chemotherapy for lung cancer. She had an 80 Pack-year history of smoking. There were no occupational exposuresOn examination, patient was visibly Dyspneic requiring 40% Oxygen. Her Heart rate was 118/min, Respiratory rate 24/min, Temperature 37.2 degrees and Blood pressure 134/76. Pertinent positives included grade 1 clubbing and Bibasilar end-inspiratory crackles. There were no signs of heart failure.Labs showed a normal White cell count and differential, basic metabolic panel. Thoracic CT showed a shrinking tumor in left upper lobe and diffuse ground glass and interstitial lung disease away from the primary tumor itself.Pulmonary function studies revealed mild restriction. DLCO could not be performed. Bronchoalveolar lavage revealed large atypical cells with vacuolated cytoplasm, prominent nucleoli and enlarged nucleus and CD-4/CD-8 ratio of 7 on flow cytometry. Transbronchial lung biopsy from Right lower lobe showed areas of organizing eosinophilic exudate. There was patchy mild fibrosis in other areas with occasional enlarged stromal cells. Focal squamous metaplasia was also noted. Tests for routine infections were negative. A diagnosis of radiation induced Hypersenstivity Pneumonitis was made and patient was started on 40mg prednisone. When followed 6 weeks later, she was on a prednisone taper and back to her baseline functional status and Oxygen requirement.
DISCUSSIONS: Hypersenstivity Pneumonitis is a less common and unpredictable lung injury has also been described that may involve areas of the lung outside the radiation port. Investigators have described a CD4+ lymphocytic alveolitis and increased gallium uptake in both irradiated and nonirradiated lung, consistent with a hypersensitivity pneumonitis-like reaction. In a study of breast cancer patients who received unilateral thoracic radiation, the early development of a bilateral hypersensitivity reaction (as assessed by bronchoalveolar lavage) appeared to be a common phenomenon, but does not predict progression to clinically significant radiation pneumonitis. Stereotactic Body Radiation(SBR)is considered safer because of lower lung volumes exposed. Although, radiation pneumonitis has reported with SBR and typically presents late(median 5 months), Hypersenstivity pneumonitis(HP) presenting as early diffuse interstitial lung disease away from radiation port has not been reported with SBR. HP is diagnosed with a lymphocytic alveolitis and increased CD4/CD8 ratio as seen in our patient. The disease entity is distinct from radiation pneumonits in terms of timing, severity, radiologic appearance, pathogenesis and clinical course. In this case a favorable response to corticosteroids was noticed.
CONCLUSION: Hypersenstivity Pneumonitis is a previously unreported adverse reaction to stereotactic body radiation for lung cancer. It presents early with diffuse interstitial lung disease away from the primary port of radiation. Clinical severity is mild to moderate and there is good response to corticosteroids.
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