PPIA and head and neck cancer: After irradiating the ten CRC cell lines, we evaluated the expression stabilities of 14 candidate RGs including the 6 genes used in the 22 studies (Fig. 1) and 8 genes (B2M, G6PD, HMBS, IPO8, PGK1, PPIA, TFRC, and YWHAZ) recently studied for radiation stability in 6 different cancer cell lines, which included head and neck cancer, non-small cell lung cancer, and pancreatic cancer cell lines26.