1097 - Response Rate and Local Control of Response-Adapted Very Low Dose Radiotherapy (RA-VLDRT) with 4 Gy for Indolent Non-Hodgkin Lymphoma
Presenter(s)
N. P. Mankuzhy1, B. S. Imber1, J. Lee2, P. Pammer3, B. Fregonese1, A. Cajo1, G. Cederquist1, A. Dreyfuss1, K. Lapen1, R. R. Patel1, Z. R. Moore1, C. Hajj4, A. Zelenetz5, Z. Zhang2, G. Salles5, and J. Yahalom1; 1Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, 2Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York, NY, 3Drexel University College of Medicine, Philadelphia, PA, 4Radiation Oncology, Oncology Institute, Cleveland Clinic Abu Dhabi, Abu Dhabi, United Arab Emirates, 5Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, NY
Purpose/Objective(s): Radiotherapy (RT) is highly effective in indolent non-Hodgkin lymphomas (iNHL) for palliation and potentially for cure in early-stage disease. Very low dose RT (VLDRT) of 4 Gy has gained overall enthusiasm for iNHL, but 24 Gy remains the NCCN standard for potentially curable disease. Given VLDRT’s advantages, our institution uses a response-adapted (RA-VLDRT) approach for both palliative and curative intent. Early response assessment (ERA) is completed around 12 weeks after VLDRT to assess response to 4 Gy and need for additional RT. We analyzed a large series of RA-VLDRT in iNHL comparing outcomes of curable and non-curable cases using 4 Gy in 1 or 2 fractions (fx).
Materials/Methods: We identified patients (pts) with iNHL treated at our center with 4 Gy in 1 or 2 fx who underwent ERA for the treated lesions. Pts were considered curable if they had untreated stage I-II or localized (skin) disease treated comprehensively with RA-VLDRT. Overall response rate (ORR) was determined at ERA (clinically or Lugano criteria) and compared via Chi-squared test. Cumulative incidence of local progression (LP; progression in the RT field) was estimated on a lesion level from RT date with death as a competing risk and compared via Gray’s test.
Results: From 2005-2024, 1025 lesions were irradiated in 813 pts; 311 lesions (30%) were in curable pts. VLDRT was given in 2 fx (772, 75%) or 1 fx (253, 25%) and 93% were PET staged. iNHL subtypes were predominantly follicular lymphoma (FL, 54%), marginal zone lymphoma (MZL, 34%), and iNHL not specified (7%). 641 (63%) lesions were extranodal (EN), 354 (35%) nodal, and 30 (3%) mixed. ERA included PET (67%), clinical exam (22%), and CT/MRI (7%). 21 lesions were excluded from ORR due to lack of evaluable residual lesion pre-RT. At ERA, ORR was 91% (65% complete response; 26% partial response) and 6% were recommended additional RT due to insufficient early response. 2- and 5-year (yr) LP were 17% (95% CI 15-20%) and 26% (95% CI 22-29%). Curable lesions (vs. non-curable) had superior ORR (p=0.003) and lower LP probability (p<0.001). There was insufficient evidence to suggest ORR (p>0.9) and LP (p=0.11) differed between 2 vs 1 fx (Table 1).
Conclusion: In this large experience of RA-VLDRT for iNHL, we observe a very high response rate to only 4 Gy with no difference in local control whether given in 1 or 2 fx. Superior outcomes in curable lesions are reassuring that an adaptive approach is safe and feasible beyond palliation. Our ongoing research is investigating genomic features influencing response to allow further personalization. These results support investigating RA-VLDRT in potentially curable pts in the upcoming ILROG Phase 3 randomized trial.
Abstract 1097 - Table 1| Curable | Non-curable | 2 Gy x 2 | 4 Gy x 1 | |
| ORR % (95% CI) | 95% (92%, 97%) | 89% (87%, 91%) | 91% (89%, 93%) | 91% (86%, 94%) |
| 2-yr LP (95% CI) | 7% (4%, 10%) | 21% (18%, 24%) | 18% (15%, 21%) | 14% (9%, 19%) |
| 5-yr LP (95% CI) | 16% (10%, 23%) | 29% (25%, 33%) | 27% (23%, 30%) | 20% (14%, 27%) |