2529 - Prognostic Factors for Early Demise Following Palliative Spatially Fractionated Radiotherapy

J. N. Hobson¹, D. K. Ebner¹, M. Grams¹, R. W. Mutter¹, S. S. Park¹, D. J. Ma¹, M. G. Haddock¹, I. A. Petersen¹, S. K. Ahmed², S. C. Lester¹, A. W. Rajkumar³, M. E. Gamez¹, D. Owen¹, and K. S. Corbin¹; ¹Department of Radiation Oncology, Mayo Clinic, Rochester, MN, ²Department of Radiation Oncology, Mayo Clinic AZ, Phoenix, AZ, ³Department of Radiation Oncology, Vanderbilt University Medical Center, Nashville, TN

Purpose/Objective(s): Spatially fractionated radiotherapy (SFRT) offers a palliative approach to managing bulky tumors by delivering alternating regions of high and low dose radiation. Reports of rapid symptom relief, tumor regression, and durable local control have been reported. Patients with limited life expectancy may have a shorter-term benefit from SFRT effects. To better inform patient selection for SFRT, those who died within 120 and 30 days of SFRT were retrospectively evaluated for prognostic factors. Materials/

Methods: A retrospective review of patients treated with SFRT, including brass and lattice, between 2019 and 2023 was performed, with analysis of those who died within 120 and 30 days of treatment. Primary histology, treatment site, ECOG status at time of SFRT, prior and concurrent systemic therapy, and 30-day hospitalization rates were assessed. As rapid tumor regression carries risk for tumor lysis, available lab values including CBC, BMP, calcium, albumin, CRP, and uric acid within two weeks before and after treatment were compared. Additionally, rates of atrial fibrillation (AFib) before and after SFRT were reviewed. Student t-test and Kaplan-Meier were employed for analysis.
Results: Of 306 patients treated with SFRT, 97 (32%) and 30 (10%) died within 120 and 30 days of treatment respectively. Of the 97 patients, 80% had metastatic disease at treatment, with ECOG 0 (12; 12.5%), 1 (33; 34.4%), 2 (28; 29.2%), 3 (21; 22.9%), and 4 (2; 2.1%). Higher ECOG status was associated with 30-day hospitalization (p<0.001), overall death (p<0.001), and death within 30 days (p=0.003). 30-day hospitalization, including those who received SFRT as inpatients (29) and those admitted within 30 days of treatment (32), was associated with overall death (p<0.001). 63 (64.9%) received chemotherapy prior to SFRT (6 concurrently) and 54 received immunotherapy (55.7%; 12 concurrently). Although changes between pre- and post-SFRT Na (p=0.019) and Cl (p=0.019) levels were observed in patients who died within 30 days, lab values did not reflect changes expected with tumor lysis. Experiencing AFib post-SFRT was not associated with survival time (p=0.128), however history of AFib was (p=0.01). 14 patients experienced AFib post-SFRT, 8 dying within 30 days, of whom 7 had a prior history of AFib.
Conclusion: Higher baseline ECOG status and hospitalization during or within 30 days of SFRT were predictive of death within 120 days of treatment. No lab indications of tumor lysis contributing to decline were seen. The impact of AFib history on survival time likely reflects pre-treatment comorbidities. While SFRT appears to be safe, baseline functional status should be considered in evaluating which patients will derive benefit from SFRT over alternative palliative measures. Further work is warranted to optimize patient selection.