Case Study: Radiation-Induced Pneumonitis Following SBRT

Case Study: Radiation-Induced Pneumonitis Following SBRT

A 67-year-old male with a history of prostate cancer and chronic obstructive pulmonary disease (COPD) was diagnosed with left upper lobe (LUL) squamous cell carcinoma after a chest CT scan revealed a 2.5-cm suprahilar mass. The patient, a former smoker with a 40 pack-year history, was asymptomatic at the time. Bronchoscopy confirmed an endobronchial LUL mass, which was diagnosed as squamous cell carcinoma (PD-L1 expression 0%). Mediastinal lymph node biopsy (station 7) was negative for malignancy. Due to significant comorbidities, including COPD and cardiovascular disease, the patient was deemed inoperable. No significant autoimmune issue was noted. Approximately one month after presentation, the LUL mass was treated with SBRT, 45 Gy in five fractions (BED₁₀ = 85.5 Gy). This slightly conservative schedule was chosen to spare the proximal airway and residual lung in a patient with COPD and a heavy smoking history, a risk-adapted approach used for central or high-risk lesions when a BED₁₀ ≥ 100 Gy cannot be delivered safely. CT performed two months later showed reduction in mass size. Six months post-treatment, he developed shortness of breath (SOB) and later experienced a cerebrovascular accident (CVA), leading to a diagnosis of left lung collapse with post-obstructive volume loss. Imaging and bronchoscopy indicated radiation pneumonitis rather than recurrent malignancy, with symptoms stabilized after prednisone therapy.

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Context of NSCLC Treatment and SBRT

Non-small cell lung cancer (NSCLC), accounting for 85% of lung cancer cases, often requires treatment options like SBRT for inoperable patients. Estimated new cases and deaths from lung cancer (NSCLC and SCLC combined) in the United States in are 226,650 new cases and 124,730 deaths. Lung cancer is the leading cause of cancer-related mortality in the United States. The 5-year relative survival rate from 2014 to 2020 for patients with lung cancer was 27%, varying by stage: 64% for local, 36% for regional, and 9% for distant. NSCLC arises from epithelial cells of the lung, with squamous cell carcinoma typically originating near central bronchi. SBRT, a high-dose radiation therapy, is a standard treatment for early-stage NSCLC in patients unsuitable for surgery. In this case, the patient’s COPD and smoking history influenced the decision to use a conservative SBRT schedule, balancing tumor control with minimizing lung injury. Despite the treatment’s success in reducing the mass, the development of pneumonitis underscores the trade-offs in managing complex cases.

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Mechanisms of Radiation-Induced Fibrosis and Pneumonitis

Radiation-induced fibrosis (RIF) is a late effect of radiotherapy, driven by inflammation and fibroblast transdifferentiation into myofibroblasts, which produce excess collagen and reduce tissue compliance. A review highlights that RIF severity correlates with radiation dose, fraction size, and treatment volume. In this case, the patient’s pneumonitis likely resulted from radiation-induced fibrosis and tumor regression causing bronchial obstruction. The study also notes that genetic factors, such as variants in the ATM gene, may predispose individuals to RIF, though this was not explicitly evaluated in the case report. Radiation injury triggers inflammation, leading to fibroblast activation and excessive collagen deposition, which compromises tissue function. In head and neck cancer patients, RIF can cause significant cosmetic and functional impairment, though its impact on lung tissue is less well characterized.

Implications for Future Treatment Approaches

The case underscores the need for personalized treatment strategies in NSCLC patients with comorbidities. While SBRT is effective, its risks—such as pneumonitis and fibrosis—must be carefully managed. Radiation injury triggers inflammation and ultimately stimulates transdifferentiation of fibroblasts into myofibroblasts. In addition to their excessive proliferation, these myofibroblasts produce excess collagen and other extracellular matrix (ECM) components, which is compounded by a reduction in remodeling enzymes. Subsequent fibrosis reduces tissue compliance and—in a majority of cancer patients and particularly those with head and neck cancer—causes cosmetic and functional impairment that significantly impacts quality of life. However, the lack of standardized protocols for managing RIF highlights the need for further research into preventive and therapeutic strategies. Clinicians should continue to weigh the benefits of SBRT against its risks, particularly in patients with preexisting lung conditions.

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Practical Next Steps

Patients experiencing symptoms such as shortness of breath or chest pain after radiation therapy should consult qualified professionals for evaluation. While this case illustrates the challenges of radiation-induced pneumonitis, individual outcomes depend on factors such as treatment details, comorbidities, and genetic predispositions. Readers are advised to seek personalized medical advice rather than relying on generalizations from case reports or studies.