J. P. Harris1, N. Abi-Jaoudeh2, C. Boyd2, M. Shi1, M. P. Reilly1, A. B. Simon1, S. N. Seyedin1, E. Healy1, C. McLaren3, M. Nagasaka4, R. Banker4, and A. M. Chen1; 1Department of Radiation Oncology, University of California - Irvine, Orange, CA, 2Division of Vascular and Interventional Radiology, Department of Radiological Sciences, University of California - Irvine, Orange, CA, 3Department of Medicine, University of California - Irvine, Orange, CA, 4Division of Hematology and Oncology, University of California - Irvine, Orange, CA
Purpose/Objective(s): Although stereotactic body radiation therapy (SBRT) is widely utilized for lung metastases, achieving local control while minimizing adverse events is challenging in certain settings. Pulsed electric field (PEF) ablation was proposed as a potentially safe approach to treating lung tumors near critical normal tissues, but there are little data on outcomes. We set out to determine the feasibility of combining electric ablation with PEF and single-fraction 12 Gy delivered with SBRT technique within 15 days. Materials/
Methods: A prospective pilot study of combined SBRT and PEF for patients with primary or metastatic lung tumors of any histology was done at a single institution. Adult patients with 1-3 target tumors up to 6 cm in size were included. Following PEF on day 1, SBRT (12 Gy in 1 fraction) was done between day 8 and 15. The primary objective was feasibility. Results: From March 2023 to September 2023, 6 patients with 8 tumors were enrolled. Histology included NSCLC (n=2), head and neck SCC (n=2), colorectal adenocarcinoma (n=1), and acinic cell carcinoma (n=1). There were 3 ultracentral (<1 cm from proximal bronchial tree), 2 central (<5 mm from heart), and 3 peripheral tumors. A median of 2 probes were used at a depth of 9.9 cm (range 6-15.5 cm) with 500 pulse cycles (range 400-1400). All patients completed the treatment course, with SBRT occurring a median of 9 days after PEF ablation (range 8-10 days). The median gross tumor volume (GTV) was 4.3 mL (range 2.9-16.7 mL), dose maximum 134% (range 132-143%), and proximal bronchial tree maximum 8.8 Gy (range 1.5-15.1 Gy). At 3 months, there were no significant changes in FVC (p=0.68), FEV1 (p=0.16), or DLCO (p=0.30). One patient had a DLCO decline of 7.2 mL/mmHg/min, which was associated with development of widespread off-target lung progression. Treatment-related adverse events included one case of grade 3 surgical procedure complication, where a patient with a history of chemoradiation for hypopharyngeal carcinoma experienced laryngeal edema preventing extubation until 1 day post-procedure. Other treatment-related adverse events were grade 1 non-cardiac chest pain (n=1) and grade 1 pneumothorax (n=2, intercostal catheter not required). There were no observations of esophagitis, pneumonitis, or any grade 4-5 event. With a median follow up of 7 months (range 6-10 months), the 6-month PFS was 67% (95% CI 19%-90%), and there were no deaths. One patient with colorectal metastases experienced distant progression at 1 month and local progression at two treated sites at 5 months. The cumulative local failure at 6 months was 25% (95% CI 31%-93%). Conclusion: In this prospective trial, treatment of predominantly central lung metastases with PEF ablation and single-fraction SBRT within 15 days was feasible and well-tolerated. A higher dose of SBRT may be required when combined with electric ablation. Longer follow up for local control is anticipated.
