Organizing pneumonia after stereotactic ablative radiotherapy of the lung

Abstract

Background: Organizing pneumonia (OP), so called bronchiolitis obliterans organizing pneumonia after postoperative irradiation for breast cancer has been often reported. There is little information about OP after other radiation modalities. This cohort study investigated the clinical features and risk factors of OP after stereotactic ablative radiotherapy of the lung (SABR).

Methods: Patients undergoing SABR between 2004 and 2010 in two institutions were investigated. Blood test and chest computed tomography were performed at intervals of 1 to 3 months after SABR. The criteria for diagnosing OP were: 1) mixture of patchy and ground-glass opacity, 2) general and/or respiratory symptoms lasting for at least 2 weeks, 3) radiographic lesion in the lung volume receiving < 0.5 Gy, and 4) no evidence of a specific cause.

Results: Among 189 patients (164 with stage I lung cancer and 25 with single lung metastasis) analyzed, nine developed OP. The incidence at 2 years was 5.2% (95% confidence interval; 2.6-9.3%). Dyspnea were observed in all patients. Four had fever. These symptoms and pulmonary infiltration rapidly improved after corticosteroid therapy. Eight patients had presented with symptomatic radiation pneumonitis (RP) around the tumor 2 to 7 months before OP. The prior RP history was strongly associated with OP (hazard ratio 61.7; p = 0.0028) in multivariate analysis.

Conclusions: This is the first report on OP after SABR. The incidence appeared to be relatively high. The symptoms were sometimes severe, but corticosteroid therapy was effective. When patients after SABR present with unusual pneumonia, OP should be considered as a differential diagnosis, especially in patients with prior symptomatic RP.

Figure 1

Five clinical states and transitions in the multi-state model. The multi-state model was developed with five clinical states: the index SABR, RP, OP, death and other thoracic irradiation. Each arrow denotes the transition between two clinical states. A transition to RP (gray arrow) was considered as an intermediate event.

Figure 2

The incidence of OP after SABR. CI denotes confidence interval.

Figure 3

Chest CT, radiograph and dose distribution of SABR of an 82-year-old patient. Blue represents areas receiving more than 0.5 Gy (Figure 3a, b). The patient presented with RP around the tumor 8 months after SABR (Figure 3c, d arrow). OP occurred 3 months after RP resolution (Figure 3e, f arrow head). Opacity around the tumor did not increase significantly (Figure 3e, f, arrow). After administration of 5 mg prednisone, symptoms and radiological findings improved (Figure 3g, h).

Figure 4

Incidence of OP after SABR in patients with (+) and without (−) prior symptomatic RP in multi-state model. CI denotes confidence interval.