Method to determine in a quantitative way stored amounts of radiation energy making use therefor from a personal monitor storing absorbed incident radiation energy in a storage phosphor panel storing radiation energy originating from radiation having a wavelength of 350 nm or less, wherein the panel is covered with an optical filter absorbing radiation having a wavelength of 350 nm or more during exposure and present in a housing, and from an apparatus for readout of the storage phosphor panel by the steps of entering the personal monitor in a read-out apparatus, removing optical filter covering the storage phosphor panel, adding stimulating energy to the storage phosphor panel, digitally detecting energy released from the storage phosphor panel by a detector and erasing stored rest energy.