Fig. 1

Cells have different radiosensitivities during different cell cycle phases. Cells during M phase have the highest sensitivity, as all chromosomes are condensed and packed in the middle of nucleus to form a bigger target, all the DNA repair mechanisms are shut down. On the contrary, all the chromosomes are very loose, and the DNA repair machineries are activated during S phase, so cells during S phase are most resistant to radiation. HPV+ OPSCC pass G1 and S phases quickly and accumulate at M Phase