Room: AAPM ePoster Library
To investigate whether spatially-fractionated radiation therapy is superior to uniform radiation in eliciting abscopal effect in an untreated tumor when combined with immune checkpoint inhibitor therapy.
An immune competent dual-tumor model of six-week old female C57BL/6 mice injected on both flanks with murine mammary adenocarcinoma (EQ771) cells. The right tumor is the primary tumor and targeted for radiation while the left tumors is untreated. 10Gy-UniformRT +/- anti-PD-L1, 50Gy-MinibeamRT +/- anti-PD-L1, and a control group were used. Four dose of 200µg anti-PD-L1 was given on day 0,3,6,9 after a single radiation. The 10 or 50Gy are the surface maximum dose. The minibeam width is 0.31mm and c-t-c distance is 1.21mm. Spleen and both the treated and untreated tumors are harvested (~5 animals per group) 14 days post-radiation for flow-cytometry immunophenotypic analysis (Cd45+, CD3+, CD4+, CD8+ cells and additionally B cells and NK cells for the spleen tissues). Tumor growth of both tumors was monitored by tumor volume change measured by digital caliper.
For the treated tumor, 10Gy-UniformRT appears to have superior tumor growth control compared to the 50Gy-MinibeamRT, with or without anti-PD-L1 drug. For the untreated tumor, in the absence of anti-PD-L1 drug both the 10Gy-UniformRT and 50Gy-MinibeamRT showed no difference in tumor growth compared to the control group. When combined with anti-PD-L1 drug only the 50Gy-MinibeamRT showed the abscopal effect, a statistically significant reduction of tumor size for the untreated tumor. When combined with anti-PD-L1 therapy the 50Gy-MinibeamRT group showed elevated CD8+ cell population compared to the 10Gy-UniformRT group, which is consistent with the observed abscopal effect from the 50GyMinibeamRT group.
Our study shows that when combined with anti-PD-L1 therapy spatially-fractionated radiation therapy is superior to uniform radiation in eliciting abscopal effect. However, uniform radiation is superior to minibeam radiation for treated tumor growth control.
Not Applicable / None Entered.