Main Session
Sep 28
PQA 02 - Lung Cancer/Thoracic Malignancies, Patient Reported Outcomes/QoL/Survivorship, Pediatric Cancer

2459 - Secondary Imaging Analysis of a Clinical Trial Combining SABR and PEF Ablation for Central Lung Tumors

04:45pm - 06:00pm PT
Hall F
Screen: 18
POSTER

Presenter(s)

Nicholas Peterson, MD - University of California, Irvine, Orange, CA

N. V. Peterson1, P. Khosravi2, X. Xie3, G. K. Harada1, A. N. Munjal1, J. Park1, K. S. Hanubal1, M. Nagasaka4, and J. P. Harris1; 1Department of Radiation Oncology, University of California - Irvine, Orange, CA, 2Department of Computer Science, University of California Irvine, Orange, CA, 3university of California, Irvine, irvine, CA, 4Division of Hematology and Oncology, University of California - Irvine, Orange, CA

Purpose/Objective(s): Stereotactic ablative radiation (SABR) is an effective treatment for lung tumors, but its safety and efficacy are limited for centrally and ultra-centrally located tumors. To address this, our group conducted a phase I trial combining dose de-escalated SABR (12Gy/1fraction) with pulsed electric field (PEF) ablation (NCT05555342). This secondary analysis seeks to quantify lung fibrosis following PEF ablation combined with SABR, as fibrosis can both hinder oxygen transfer and complicate tumor assessment.

Materials/Methods: The follow up CT at six months post-end of radiation was used for fibrosis analysis. Ipsilateral lung and tumor volumes were delineated. Using a range lock of at least -700 HU, fibrosis was contoured on the follow up scan in the irradiated lung volume by a radiation oncologist. Fibrosis ratio was defined as the ratio of fibrosis volume to residual tumor volume. Contouring and generation of imaging statistics were performed with MIM (version 7.2.3). Statistical analysis was performed using R Studio (version 4.2.1). Wilcoxon signed-rank tests were used to compare groups.

Results: A total of 19 tumors were included in the imaging analysis. The SABR monotherapy cohort contained 10 patients with 11 tumors. The SABR-PEF cohort contained 6 patients with 8 tumors. The mean interval from planning CT to follow up CT was 193 days (IQR 161.5–238.5d). The mean BED10 was 111Gy (IQR 100-106Gy) for the SABR monotherapy cohort and 26.4Gy for the SABR-PEF cohort. Mean fibrosis volume was 44.9cc (IQR 11.3-85.7cc) for the SABR monotherapy cohort and 11.7cc (IQR 6.6-16.0cc) for the SABR-PEF cohort (p=0.14). There was a significant difference in fibrosis ratio between the SABR monotherapy cohort (mean 17.34) and SABR-PEF cohort (mean 1.34, p = 0.03). There was a trend for a decrease in HU intensity with the SABR-PEF cohort (75th percentile HU -65.1 vs 8.9, p=0.057). Linear regression demonstrated that BED10 was significantly associated with increased fibrosis volume (?=0.43, p=0.008). For each increase in 1Gy BED, fibrosis volume increased by approximately 0.48cc.

Conclusion: Our findings demonstrate that the combination of dose de-escalated SABR with PEF ablation results in smaller fibrosis volume, ratio of fibrosis to residual tumor, and may decrease fibrosis intensity compared to high-dose SABR monotherapy. These findings suggest that combination therapy methods with reduced dose SABR may better enable tumor assessment and perhaps reduce pneumonitis risk.