1983P - Palliative spatially fractionated stereotactic radiation therapy (Lattice) for large sarcoma

Background

Awareness and respective publication numbers on Spatially Fractionated RT (SFRT) rapidly increased over the past years. Lattice Radiotherapy (LRT) as one form of SFRT is a promising treatment option for patients with large inoperable and/or metastatic tumors. Since first reports on clinical LRT use in ∼2010, all confirm unexpectedly high tumor responses with excellent treatment tolerance. Questions regarding best dose-volume/fractionation/geometrical solutions are unanswered - several approached are in early testing. Similarly, knowledge regarding outcome over time (extent, duration of treatment effects) are hardly known yet. Only few case reports were published on LRT in sarcoma. We aimed to assess early outcome of a multi-center retrospective sarcoma patient cohort treated with LRT.

Methods

This retrospective cohort analysis included 22 palliative patients treated from 08.2020-04.2023 with LRT for 28 large (>10cm) sarcomatous lesions of different subtypes. Data were prospectively collected. LRT was performed at 2 Centers (A: Instituto Oncobio, Minhas Gerais (Brazil), B: LUKS Universitary Teaching Hospital (Switzerland)). Mean/median GTV measured 1029/780cc (74-4778). Center A used 1 single fraction with doses of 15-20Gy to the intra-lesional vertices, followed by 5 (n=6) or 15-16 fractions (n=4) with 25Gy or ∼40Gy respectively, to the entire tumor. Center B applied 5 fractions of 20-25Gy to the entire tumor with a simultaneous integrated boost dose of 60-65Gy to the vertices. Follow up intervals of this palliative cohort had to be adjusted to the individual situation. Primary outcome measure included subjective early clinical effect and objective tumor shrinkage.

Results

Mean/median FU was 7.1/6 mo. (0.5-24). 7/22 pats died after mean 4 mo. (0.5-6). Subjective statements at LRT completion were available in all pats: no change in 2/22, substantial fast relief of symptoms in 20/22; no >G1 side effects. FU imaging was assessable from 20/28 lesions: mean/median shrinkage of 43/25% (0-100%) after mean/median 7/3.5 mo. (0.5-22), including 9 lesions with previous RT.

Conclusions

LRT in sarcoma translated into fast subjective symptom relief and related objective tumor shrinkage. A phase 2 trial is provided to test different LRT schedules.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.