A Case of Bilateral Radiation Pneumonitis and Post Radiation Pulmonary Fibrosis One Month After Unilateral Lung Radiation

Introduction: Radiation induced pulmonary fibrosis typically develops between 6-12 months after completion of radiation therapy (RT), and typically affects only the irradiated lung. We present a rare case of bilateral radiation induced pulmonary fibrosis occurring only one month after completion of unilateral RT. Case Presentation: A 75-year-old male with pleural mesothelioma treated with five cycles of neoadjuvant carboplatin and pemetrexed followed by thoracotomy, pleurectomy, decortication and six weeks of RT (28 fractions, total 50.4 Grays) (Figure 1A) presented 33 days after completing RT with five days of dyspnea and dry cough. Vitals were notable for oxygen saturation of 86% on room air with improvement to 97% on 4 L/min via nasal cannula. Review of his pre-RT computed tomography (CT) demonstrated left-sided bronchiectasis and basilar ground glass attenuation representing post-inflammatory changes (Figure 1B). Repeat CT 27 days after completion of RT showed new bilateral diffuse ground-glass opacities with left upper and lower lobe fibrosis (Figure 1C);CT upon current presentation revealed increased ground-glass opacities and bilateral fibrosis (Figure 1D). Blood cultures, SARSCoV-2 PCR, respiratory pathogen panel (including influenza A/B and respiratory syncytial virus), cryptococcal antigen, galactomannan and 1,3-beta-d-glucan were all unrevealing. Transthoracic echocardiogram revealed septal E/e' ratio 12.6 and estimated pulmonary artery systolic pressure 30 mmHg, and serum b-type natriuretic peptide level was 48 pg/ml. Detailed reconciliation confirmed he was not taking any new medications, including statins. Hypersensitivity pneumonitis panel was negative. His working diagnosis was radiation induced lung injury with features of both early pneumonitis and late fibrosis. Therapy with short-acting bronchodilators and systemic corticosteroids was initiated with significant clinical improvement;patient was discharged home on hospital day six off oxygen. Discussion: Radiation induced lung injury can generally be divided into acute and late phases. The former is commonly known as radiation pneumonitis and manifests as ground-glass opacities 4-12 weeks after completion of RT, and the latter presents as bronchiectasis and fibrosis 6-12 months later. Ours is a rare case of pneumonitis and fibrosis that developed within one month of completing RT. Additionally, this patient developed pneumonitis and fibrosis of his right lung, which did not receive any radiation;very few cases of pneumonitis on the nonirradiated lung have been reported. Immunologically mediated lymphocytic alveolitis has been proposed as a mechanism for contralateral spread of radiation fibrosis. Our patient showed significant clinical improvement with initiation of corticosteroids with the plan for a long, slow outpatient taper based on clinical response.