2670 - Esophagitis and Pharyngitis after Re-Irradiation Spine SBRT of 24Gy in 2 Fractions

Purpose/Objective(s): Although pharyngitis and esophagitis are associated with stereotactic body radiation therapy (SBRT) for spinal metastases, their incidence in particularly high-risk, re-irradiation cases is unknown. The present study therefore retrospectively analyzed their incidence and risk factors.

Materials/Methods: Spine SBRT cases including C1 to T10 with a history of conventional irradiation in the overlapping area were included in the study. The SBRT dose was limited to 24 Gy in two fractions. The pharynx and esophagus were contoured by treatment planning CT, no PRV margin was applied, and the following dose constraints were basically used: pharyngeal D_{1 cc} < 20 Gy, esophageal D_max < 24 Gy, and D_{2.5 cc} < 19 Gy. Adverse events were graded using CTCAE ver. 5.0, with grade 2 or higher being defined as an event. Patients receiving irradiation at the pharyngeal level (C1 to C6) and those receiving irradiation at the esophageal level (C7 to T10) were evaluated for pharyngitis and esophagitis, respectively. In patients with irradiation of both C6 and C7, inflammatory symptoms were counted as both pharyngitis and esophagitis.

Results: Ninety-five (62 males and 33 females) patients were included. The median follow-up was 15 (range: 3–111) months; the median age was 66 (range: 34–87) years; the ECOG performance status (PS) was 0, 1, 2, 3, and 4 in 32, 42, 14, 3, and 4 patients, respectively; the previously delivered, median BED3 dose was 62.2 (range: 12–220) Gy; and the median irradiation interval was 17 (range, 10–153) months. The pharyngeal level group contained 17 patients, none of whom had acute or late, grade 2 or higher adverse events. The esophageal level group contained 90 patients, of whom 22 (25.3%), one (1.1%), and four patients (4.6%) had acute grade 2, grade 3, and late grade 2 esophagitis, respectively. No grade 4 or 5 adverse events were observed. On univariate analysis, women had significantly more acute grade 2 or higher esophagitis (odds ratio: 3.30; 95% confidence interval: 1.14–9.87; p=0.023). Age, PS, the number of treated vertebrae, presence of internal fixation metal, previous irradiation dose, and irradiation interval did not differ significantly. The one-year local recurrence rate was 16.8%.

Conclusion: Severe pharyngitis and esophagitis were rare in re-irradiated spine SBRT, suggesting that the dose constraints used at our institution are safe. The present study found female sex to be a significant risk factor of grade 2 or higher esophagitis.