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radiation pneumonitis

A subacute inflammatory pneumonitis which occurs in response to exposure of the lungs to therapeutic doses of ionizing radiation. Etiology: - risk factors a) concurrent chemotherapy b) prior radiation therapy c) recent withdrawal of glucocorticoids Pathology: 1) radiation initially effects pulmonary capillary endothelial cells & type II pneumocytes 2) lymphocytic stimulation can lead to bronchiolitis obliterans with organizing pneumonia (BOOP) Clinical manifestations: 1) symptoms generally begin insidiously 1-3 months (4-12 weeks) [3] after completion of radiation 2) cough 3) dyspnea out of proportion to chest X-ray findings 4) low grade fever 5) non-specific & variable, depending upon a) total dose of radiation b) fractionation schedule c) volume of lung irradiated d) concomitant administration of cytotoxic agent - bleomycin - cyclophosphamide e) withdrawal of steroids Laboratory: - arterial blood gas - impairment of gas exchange in more severe cases Special laboratory: - pulmonary function testing - decreased DLCO in more severe cases Radiology: - chest radiograph: - new infiltrate corresponding to region of radiation exposure - non anatomic straight line demarcating involved vs non-involved lung parenchyma is pathognomonic [3] - CT of thorax - hazy opacities with ground glass attenuation - distribution conforms to radiation port rather than anatomical lobes of the lung or bronchopulmonary segments - air bronchograms with slight dilation of peripheral bronchi Complications: - abnormalities may resolve within 6 months or progress to pulmonary fibrosis, volume loss & bronchiectasis [3] Differential diagnosis: 1) infections 2) recurrent tumor 3) lymphangitic carcinoma Management: 1) mild symptoms a) cough suppressants b) antipyretics c) rest 2) moderate to severe disease a) glucocorticoids [3] - start prednisone 60-100 mg/day for 3-5 days - 20-40 mg prednisone/day for 2-4 weeks - taper prednisone to none after 4 weeks b) only 50-80% will respond to glucocorticoid therapy [3]

Related

radiation therapy (XRT)

General

pneumonitis radiation injury; radiation toxicity

References

  1. Manual of Medical Therapeutics, 28th ed, Ewald & McKenzie (eds), Little, Brown & Co, Boston, 1995, pg 256
  2. Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 762
  3. Medical Knowledge Self Assessment Program (MKSAP) 15, 16, 17, 18, 19. American College of Physicians, Philadelphia 2009, 2012, 2015, 2018, 2022.