CTICasesRadiation-Induced Organizing Pneumonia (from low-dose chest wall radiation)
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Imaging findings
This patient, treated for a lung cancer recurrence in the chest wall with tangential radiation, developed cough and dyspnea. Imaging shows well-defined, round ground-glass opacities, some exhibiting classic 'Atoll signs' (reversed halos). These opacities are distributed throughout the lung, notably in areas that received low-dose radiation, outside the high-dose primary lung treatment field (which showed stable fibrosis). Serial scans over several months demonstrate a waxing and waning course, with some areas clearing and others worsening.
Key takeaways
Radiation-induced organizing pneumonia can occur remotely from the primary high-dose radiation field, manifesting as a hypersensitivity reaction in areas of the lung that received incidental low-dose radiation (e.g., during tangential chest wall irradiation for breast or lung cancer). It typically presents with organizing pneumonia patterns, such as the 'Atoll sign', within the first year post-radiation. This entity is often under-recognized and usually responds well to corticosteroids, differentiating it from infectious pneumonia or direct high-dose radiation pneumonitis.
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