Proton irradiation tends to be more effective in reducing pancreatic ductal adenocarcinoma (PDAC) tumoroid growth than photon irradiation. (A) Experimental set-up for examining 3D PDAC tumoroid growth; (B) Representative bright-field images of unirradiated, 6-Gy photon and 6-Gy proton irradiated 3D PDAC tumoroids, scale bar: 100 µm; (C) 3D tumoroid formation capacity without irradiation; (D) 3D PDAC tumoroid growth after irradiation with 2, 4 or 6 Gy of photons and protons. Cell lines are ordered by increasing resistance to photon irradiation. Results show mean ± SD (n = 3; two-sided t-test; *, p < 0.05; **, p < 0.01).