Outcomes of Spatially Fractionated Radiotherapy (GRID) for Bulky Soft Tissue Sarcomas in a Large Animal Model

Area of Science:

• Radiation Oncology
• Veterinary Medicine
• Radiobiology

Background:

• Spatially fractionated radiotherapy, like GRID, requires large animal models for human treatment simulation.
• Pet dogs with spontaneous tumors offer a translational model for studying radiotherapy effects.

Purpose of the Study:

• To assess the safety and efficacy of GRID therapy in dogs with soft tissue sarcomas.
• To characterize the biological response to GRID, including serum marker changes.

Main Methods:

• Pilot study involving 6 pet dogs with soft tissue sarcomas treated with 20 Gy or 25 Gy GRID therapy.
• Tumor response and acute toxicity were evaluated over 6 weeks.
• Serum levels of vascular endothelial growth factor, tumor necrosis factor α, and secretory sphingomyelinase were measured at various time points.

Main Results:

• No measurable tumor volume reduction was observed following GRID therapy.
• Grade I skin toxicity occurred in 3 dogs; no significant acute toxicity was noted.
• Trends showed decreased vascular endothelial growth factor and tumor necrosis factor α, with a significant decrease in secretory sphingomyelinase at 48 hours post-25 Gy GRID.

Conclusions:

• GRID therapy at high doses is safe in canine soft tissue sarcomas but does not induce tumor shrinkage.
• GRID therapy may transiently alter serum biomarkers, suggesting its potential as a preclinical model.
• Pet dogs with sarcomas provide a valuable platform for investigating spatially fractionated radiotherapy radiobiology.