Fig. 3
Clonogenic cell survival of A549. Clonogenic cell survival of sham treated A549 cells irradiated with each of the investigated radiation modalities (A) and the corresponding dose to achieve SF50, SF25, and SF10 (B). Importantly, no statistical significant difference can be observed in sham treated A549 cells. Similar clonogenic data obtained in A549 cells treated with 2 nM ganetespib (C) highlights a proton-exclusive radiosensitizing effect. This sensitization by 2 nM ganetespib significantly reduces the dose required to reach SF50, SF25, and SF10 in A549 cells irradiated with proximal and distal SOBP protons compared to reference photon IR (D). Consequently, the RBE of both proton modalities is significantly higher by 10–40% in A549 cells upon ganetespib treatment compared to sham treatment (E–G). Proximal and distal SOBP corresponds to a LET of 2.1 respectively 4.5 keV/μm and statistical testing was performed by unpaired, two-tailed t-test with Welch’s Correction with error bars indicating the standard deviation