Stereotactic Ablative Radiation Therapy (SABR) for Adolescent and Young Adult Malignancies.

Background: There are limited studies examining local control (LC) and overall survival (OS) following stereotactic ablative radiation therapy (SABR) for adolescent and young adult (AYA) populations/histologies with local recurrences or metastatic disease.

Methods: The RSSearch® Patient Registry, an international SABR registry, was evaluated for AYA patients treated with SABR. AYA patients with adult histologies/primaries were excluded. Kaplan-Meier analyses were employed to characterize LC and OS following SABR. Potential prognostic factors were assessed with log-rank tests for initial univariate analysis (UVA). For multivariate analyses (MVA), a Cox proportional hazards multivariate model was utilized.

Results: A total of 19 AYA patients with 39 lesions treated with SABR were identified and included in the analysis. Four lesions (10.3%) were treated with SABR for primary tumor recurrence and 35 lesions were treated for metastatic disease. The median patient age was 34 years (range: 16-39 years). Common lesion locations included lung (11 lesions; 28.2%), non-spinal bone (nine lesions; 23.1%), and spine (six lesions; 15.4%). The median biological effective dose (BED) was 61.5 Gy (range: 26.4-180). One-year LC and OS following SABR were 77.7% (95% CI: 58.5-88.7) and 72.7% (95% CI: 46.3-87.6), respectively. On UVA, BED ≥ 60 Gy was associated with superior one-year LC (94.4% vs. 47.6%; p<0.0001) as were sarcoma primaries (two-year LC: 92.3% vs. 42.2%;p = 0.0002). Central nervous system (CNS) primaries had significantly poorer one-year LC (20% vs 87.5%; p<0.0001) as well as spinal metastases (33.3% vs. 87.0%; p<0.0001). On MVA, BED < 60 Gy was associated with inferior LC (hazard ratio (HR) = 5.51;p = 0.01) with sarcoma primaries associated with superior LC (HR = 0.04;p = 0.008).

Conclusion: SABR with BED ≥ 60 Gy resulted in durable LC for AYA patients, particularly those with sarcoma primaries, though poor outcomes were noted in metastatic CNS malignancies.