Many scientists and colleagues from abroad and Iran (listed below) voluntarily helped us very much in review and evaluation process of manuscripts being accepted for publication in 2020 issues of IJRR (Volume 18, numbers 1-4) and those not suitable for publication. Indeed their careful and critically reading the manuscripts and their valuable comments and suggestions greatly improved the quality of papers. On behalf of the executive and editorial board of the International Journal of Radiation Research (IJRR), I sincerely thank all of them for their efforts and support throughout the past years and we hope to have their continued support and help in the future.