LITE SABR M1: a Phase I Trial of Lattice Stereotactic Body Radiotherapy for Large Tumors

Abstract

Purpose: Stereotactic body radiotherapy (SBRT) is an attractive treatment option for patients with metastatic and/or unresectable tumors, however its use is limited to smaller tumors. Lattice is a form of spatially fractionated radiotherapy that may offer safe delivery of SBRT for bulky tumors. We previously described Lattice SBRT, which delivers 20 Gy in 5 fractions with a simultaneous Lattice boost to 66.7 Gy. The goal of this study was to prospectively evaluate the acute toxicity and quality of life (QoL) of patients with large tumors (> 5 cm) treated with Lattice SBRT. Methods: This was a single-arm phase I trial conducted between October 2019 and August 2020. Patients with tumors >4.5 cm were eligible. Lattice SBRT was delivered every other day then patients were evaluated for 90 days. The primary outcome was the rate of treatment-associated grade 3+ acute toxicity by Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 criteria. Other outcomes included patient reported toxicity and QoL inventories, and GTV changes following Lattice SBRT. Results: Twenty patients (22 tumors) were enrolled. Median gross tumor volume (GTV) was 783 cc (range: 64-3713 cc). Fifty percent of tumors were in the thorax, 45% abdomen/pelvis, and 5% extremity. There was no grade 3+ toxicity probably or definitely attributable to Lattice SBRT. There was one case of grade 4 toxicity possibly associated with Lattice SBRT. Conclusions: This phase I study met its primary endpoint of physician reported safety, confirmed with secondary PRO-CTCAE outcomes. Early efficacy, as demonstrated by PROMIS QoL and imaging, is encouraging. An ongoing phase II clinical trial of Lattice SBRT is evaluating the safety and efficacy of this novel technique.