1. A therapy system comprising: at least one processor programmed to: receive a planning image of a region of a subject, the subject including a target and/or an organ at risk (OAR), and the subject being associated with at least one surrogate acting as a surrogate for the target and/or the OAR, wherein the subject surrogate includes an implanted optical fiber which defines an optical fiber structure (OFS), the surrogate being the implanted optical fiber; determine a reference location and shape in the planning image for one or more of the target and/or the OAR; determine a reference location and/or shape from the planning image of each of the surrogate; determine deviations between: the reference location and/or shape of the surrogate and a current location and/or shape of the surrogate.