C. C. Huang1, Z. Wan2, D. Niedzwiecki2, and C. R. Kelsey3; 1Department of Radiation Oncology, Duke University Medical Center, Durham, NC, 2Department of Biostatistics and Bioinformatics, Duke University Medical Center, Durham, NC, 3Duke University Medical Center, Department of Radiation Oncology, Durham, NC
Purpose/Objective(s): Long-term results from SWOG S8736 and S0014 (included rituximab) demonstrated late systemic relapses after CHOPx3 + RT (40-55 Gy) in patients with aggressive non-Hodgkin lymphoma. This analysis provides a long-term update of a phase 2 trial which evaluated a lower dose of RT (20 Gy) to assess the risk of late local relapses with a lower RT dose in diffuse large B-cell lymphoma (DLBCL) and primary mediastinal B-cell lymphoma (PMBL). Materials/
Methods: Patients with DLBCL or PMBL achieving a complete response by PET-CT (Deauville 1-3) after =4 cycles of R-CHOP or R-EPOCH were eligible. Consolidation RT dose was 19.5-20 Gy. The primary endpoint of the original study was 5-year freedom from local recurrence (FFLR). Long-term outcomes were assessed including late toxicities. Results: Patients (n=62) were enrolled between 2010 and 2016. Stage distribution was: I-II (n=49, 79%) and III-IV (n=13, 21%). Bulky disease (=7.5 cm) was present in 23 patients (40%). Most (n=58, 94%) received R-CHOP. Four cycles were administered to 34% of patients while 66% received 5-6 cycles. With a median follow-up of 9 years, 8 patients progressed (1 within the RT field and 7 outside the RT field). FFLR at 5 and 10 years was 98% (95% CI 87-99%) and 98% (95% CI 87-99%). Progression-free survival at 5 and 10 years was 88% (95% CI 77-94%) and 77% (95% CI 62-87%). Overall survival at 5 and 10 years was 94% (95% CI 85-98%) and 80% (95% CI 64-89%). Secondary malignancies developed in 10 patients with one second cancer attributed to RT (basal cell carcinoma developing within RT field 10 years after treatment). Major cardiac events developed in 12 patients after chemoimmunotherapy/RT but in only two was the heart in the RT field—atrial fibrillation (mean heart dose 8 Gy) and atrial fibrillation/CHF (mean heart dose 1.5 Gy). Hypothyroidism developed in 4 (6.5%), all attributed to RT. Conclusion: Long-term results of this phase II study, with a median follow-up of 9 years, did not demonstrate late local failures when the dose of RT was reduced to 20 Gy. A larger (n=240) study from the International Lymphoma Radiation Oncology Group evaluating 20 Gy of RT after = 3 cycles of chemoimmunotherapy completed accrual in 2023.
