Hydrogenated amorphous silicon (a-Si:H) is a well known material for its radiation resistance and for the possibility of deposition on flexible substrates like Polyimide (PI), polyethylene terephthalate (PET) or polyethylene naphthalate (PEN). Due to the properties of a-Si:H its usage for dosimetry, beam monitoring for particle physics and nuclear medicine, as well as, radiation flux measurement for space applications and neutron flux measurement can be foreseen. In this paper the dosimetric X-ray response of p-i-n diodes deposited on Polyimide will be studied. In particular we will study the linearity of the photocurrent response to X-rays versus dose-rate from which we will extract the dosimetric sensitivity at various bias voltages. We will repeat this study for devices having two different areas ( 2 mm x 2 mm and 5 mm x 5 mm) also a measurement of stability of X-ray response versus time will be shown.