Radiation therapy (RT) is an essential component in the therapeutic treatment of patients with localized prostate cancer (LPCa). Besides its local effects, ionizing radiation has been linked to mechanisms leading to systemic immune activation. The present study explored the effect of RT on the T‑cell receptor variable β (TCR Vβ) chain repertoire of peripheral blood T cells in patients with LPCa. High‑throughput TCR Vβ sequencing was performed on 20 blood samples collected from patients with LPCa at baseline and 3 months post‑RT. The diversity index was altered, as were TCR Vβ clonal evenness and convergence before and post‑RT; however, these findings were not significant. Notably, marked changes in the frequencies among the top 10 TCR Vβ clonotypes were detected and some patients developed new clonotypes of high abundance. These data provided initial evidence that RT in patients with LPCa may induce systemic immune changes, which could be exploited by future therapies for improved clinical results.