The present invention relates to a method enabling quantification of dose delivery in radiotherapy treatment during patient-specific treatment of the patient utilizing measurements in predefined time-intervals with information means positioned in the radiation beam, between the patient and the source and converting the readings to corresponding measures in a phantom. The invention additionally covers the method to obtain the said calibration factors for the detectors. The said calibration factors are obtained for each information means, field and said definable time-interval simultaneously irradiating the information means and said phantom including detectors to measure the absorbed dose using the said patient-specific treatment without patient.