In conclusion, we found that CTNNB1 rs1880481, CTNNB1 rs3864004, and GSK3B rs375557 were correlative with the curative efficacy of RT, and that GSK3β rs375557 and APC rs454886 were correlative with acute grade 3–4 radiation-induced dermatitis and oral mucositis. The gene discussed is GSK3B; the disease is oral mucositis.