Achieving high-resolution spatial mapping of dose and linear energy transfer in ion-beam therapy

Objective: We present a novel detector system capable of simultaneously obtaining two-dimensional (2D) dose and linear energy transfer (LET) maps from Al 2 O 3 films of sizes up to 190x190 mm 2 using optically stimulated luminescence (OSL). Approach: The system is based on the OSL from doped Al 2 O 3 films measured using pulsed stimulation and time-resolved OSL detection. The system was calibrated in proton, 4 He-, and 12 C-ion beams. The minimal detectable dose, response homogeneity, pixel cross-stimulation, and precision were also investigated. To demonstrate the system's performance, 2D maps of dose and LET of a proton Bragg curve were measured. Main results: The system was demonstrated to be capable of obtaining absorbed dose and LET 2D maps with a spatial resolution set to 1.0x1.0 mm 2 . The system was calibrated over a clinically relevant range of LET values and characterized through assessment of minimal detectable dose (<25 mGy), readout protocols, response homogeneity, precision, and relative detector efficiency. Dose and LET were found to be measurable with precisions of 3.2% and 10%, respectively. Significance: To our knowledge, this is the first passive detector system capable of measuring LET and dose simultaneously in 2D with a 1.0 mm 2 spatial resolution and no prior dose knowledge. Such properties are required to experimentally validate simulated dose and LET distributions in ion-beam therapy, paving the way for sub-mm mapping of radiation-induced relative biological effectiveness.