Hydrogenated amorphous silicon (a-Si:H) is a material having an intrinsically high radiation hardness that can be deposited on flexible substrates such as polyimide (PI). For these properties, a-Si:H can be used for the production of flexible sensors. a-Si:H sensors can be successfully utilized in dosimetry, beam monitoring for particle physics (X-ray, electron, gamma ray, and proton detection) and radiotherapy, radiation flux measurement for space applications (study of solar energetic particles and stellar events), and neutron flux measurements. In this article, we have studied the dosimetric X-ray response of n-i-p diodes deposited on PI. We measured the linearity of the photocurrent response to X-rays versus dose rate from which we have extracted the dosimetric X-ray sensitivity at various bias voltages. In particular, low bias voltage operation has been studied to assess the high energy efficiency of these kinds of sensors. A measurement of stability of X-ray response versus time has been shown. The effect of detectors annealing has been studied. Operation under bending at various bending radii is also shown.