Single-crystal diamond detector for flattening-filter-free and small-field dosimetry: Toward transparent beam imaging in clinical radiotherapy

Accurate dosimetry in small-field and flattening-filter-free (FFF) photon beams is essential for quality assurance in modern radiotherapy, but conventional detectors often face trade-offs in spatial resolution, stability, and response linearity. Diamond offers an attractive alternative due to its wide bandgap, tissue equivalence, and radiation hardness. In this work, we characterize high-purity single-crystal chemical vapor deposition (SC-CVD) diamond detectors under clinical 6 MV and 10 MV LINAC beams. We evaluate current–voltage behavior, dose linearity, temporal stability, and output factor performance in a water phantom. The detector exhibits excellent linearity across clinically relevant dose rates (Fowler exponent ≈ 0.997), submillimeter resolution, and <0.1 % signal drift over 60 s. The device provides stable response and sub-millimeter resolution, supporting its use in small-field dosimetry. These results establish a quantitative baseline for high-purity diamond sensors in clinical dosimetry and support their integration into future transparent x-ray beam imagers with sub 50 μm spatial resolution.