%0 Journal Article %T Distance to Isocenter Directly Affects Margin and Inappropriate Margin Increases the Risk of Local Control Failure in LINAC-Based Single-Isocenter SRS or SRT for Multiple Brain Metastases %A Junfang Gao %J International Journal of Medical Physics,Clinical Engineering and Radiation Oncology %P 113-123 %@ 2168-5444 %D 2022 %I Scientific Research Publishing %R 10.4236/ijmpcero.2022.112010 %X =In the advancement of single-isocenter multiple target treatment in the LINAC-based SRS or SRT, the target distance to the isocenter and grouping of multiple targets are the highly concerned and debatable topics in the SRS/SRT field at present. Three failure and success cases of local control in our early practices are presented in this study and it indicated that the target distance to the isocenter directly affects the margin and an inappropriate margin increase the risk of local control failure. The GTV expansion margin should be LINAC-specific and institute-specific. Within the physics and dosimetry scope, the AHARA (as high as reasonably achievable) principle is the first time proposed to the radiation oncology field. Radiobiology and tumor response complexity is beyond this study. %K Single-Isocenter Multiple Target %K SRS/SRT %K AHARA %K Winston-Lutz-Gao Test %U http://www.scirp.org/journal/PaperInformation.aspx?PaperID=117287