Lost in rotation.

One of the big advantages of LINAC-based SRS is the option to use a single isocenter to treat multiple intracranial lesions. While this cuts treatment time dramatically, it introduces rotational error where targets farther from the isocenter are susceptible to higher chances of geographic miss. This error has been notoriously difficult to quantify, but after reading this paper...it’s still difficult to quantify. In this rare solo publication (complete with first person plural pronouns), we get an in-depth statistical analysis of the PTV margin necessary to account for rotational error as you get farther from isocenter. The conceptual takeaway is that potential rotational error  increases very slowly at small distances from isocenter but increases rapidly as you get to the far reaches of the brain. TBL: Generic PTV margins for single-iso, multi-target SRS may overestimate error at close distances and underestimate it at large distances, though we'll hold out for real-life clinical outcomes. | Chang, Pract Radiat Oncol 2018