title: Radiobiological mechanisms of stereotactic body radiation therapy and stereotactic radiation surgery.
abstract: Despite the increasing use of stereotactic body radiation therapy (SBRT) and stereotactic radiation surgery (SRS) in recent years, the biological base of these high-dose hypo-fractionated radiotherapy modalities has been elusive. Given that most human tumors contain radioresistant hypoxic tumor cells, the radiobiological principles for the conventional multiple-fractionated radiotherapy cannot account for the high efficacy of SBRT and SRS. Recent emerging evidence strongly indicates that SBRT and SRS not only directly kill tumor cells, but also destroy the tumor vascular beds, thereby deteriorating intratumor microenvironment leading to indirect tumor cell death. Furthermore, indications are that the massive release of tumor antigens from the tumor cells directly and indirectly killed by SBRT and SRS stimulate anti-tumor immunity, thereby suppressing recurrence and metastatic tumor growth. The reoxygenation, repair, repopulation, and redistribution, which are important components in the response of tumors to conventional fractionated radiotherapy, play relatively little role in SBRT and SRS. The linear-quadratic model, which accounts for only direct cell death has been suggested to overestimate the cell death by high dose per fraction irradiation. However, the model may in some clinical cases incidentally do not overestimate total cell death because high-dose irradiation causes additional cell death through indirect mechanisms. For the improvement of the efficacy of SBRT and SRS, further investigation is warranted to gain detailed insights into the mechanisms underlying the SBRT and SRS.
authors.affiliation: Research Center for Radiotherapy, Korea Institute of Radiological and Medical Sciences, Seoul, Korea.
authors.forename: Mi-Sook
authors.initials: MS
authors.lastname: Kim
authors.affiliation: Research Center for Radiotherapy, Korea Institute of Radiological and Medical Sciences, Seoul, Korea.
authors.forename: Wonwoo
authors.initials: W
authors.lastname: Kim
authors.affiliation: Research Center for Radiotherapy, Korea Institute of Radiological and Medical Sciences, Seoul, Korea.
authors.forename: In Hwan
authors.initials: IH
authors.lastname: Park
authors.affiliation: Research Center for Radiotherapy, Korea Institute of Radiological and Medical Sciences, Seoul, Korea.
authors.forename: Hee Jong
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Research Center for Radiotherapy, Korea Institute of Radiological and Medical Sciences, Seoul, Korea.
authors.forename: Eunjin
authors.initials: E
authors.lastname: Lee
authors.affiliation: Research Center for Radiotherapy, Korea Institute of Radiological and Medical Sciences, Seoul, Korea.
authors.forename: Jae-Hoon
authors.initials: JH
authors.lastname: Jung
authors.affiliation: Department of Radiation Oncology, University of Minnesota Medical School, Minneapolis, MN, USA.
authors.forename: Lawrence Chinsoo
authors.initials: LC
authors.lastname: Cho
authors.affiliation: Department of Radiation Oncology, University of Minnesota Medical School, Minneapolis, MN, USA.
authors.forename: Chang W
authors.initials: CW
authors.lastname: Song
keywords: Radiobiology; Stereotactic body radiation therapy; Stereotactic radiation surgery