An area integrated fluence monitoring sensor (20, 60, 70, 80) for measuring a radiation dose from an ionizing radiation beam, wherein the sensor comprises: at least one Gradient Ion Chamber (30, 62, 64, 72, 74, 82, 84, 86, 88) comprising: an ion chamber having a volume gradient across a length or width thereof; a pair of polarizing electrodes (32, 34) defining upper and lower portions of the ion chamber and providing a portion of a housing for the at least one GIC, the pair of polarizing electrodes being oriented with respect to one another to provide the volume gradient; a pair of insulator regions (46, 50) separating end portions of the polarizing electrodes from one another at opposite ends of the ion chamber; a pair of guard electrodes (40, 42) located within the insulator regions and configured to reduce the effect of leakage current on radiation dose measurement; a gas or liquid located within the ion chamber; and an electrode to detect ions generated within the gas or liquid when the at least one GIC is subjected to an ionizing radiation beam, the electrode to detect ions being a collector plate disposed between the pair of polarizing electrodes, each of the ends of the collector plate being located within one of the guard electrodes and the sensor further comprising an additional pair of insulator regions (44, 48) located within the guard electrodes to insulate the collector electrode from the guard electrodes, wherein the ion chamber has a surface area larger than a cross-sectional area of the ionizing radiation beam at the at least one GIC and the sensor encodes a location and amount of ionizing radiation provided by the radiation beam at the at least one GIC. at least one Gradient Ion Chamber (30, 62, 64, 72, 74, 82, 84, 86, 88) comprising: an ion chamber having a volume gradient across a length or width thereof; a pair of polarizing electrodes (32, 34) defining upper and lower portions of the ion chamber and providing a portion of a housing for the at least one GIC, the pair of polarizing electrodes being oriented with respect to one another to provide the volume gradient; a pair of insulator regions (46, 50) separating end portions of the polarizing electrodes from one another at opposite ends of the ion chamber; a pair of guard electrodes (40, 42) located within the insulator regions and configured to reduce the effect of leakage current on radiation dose measurement; a gas or liquid located within the ion chamber; and an electrode to detect ions generated within the gas or liquid when the at least one GIC is subjected to an ionizing radiation beam, the electrode to detect ions being a collector plate disposed between the pair of polarizing electrodes, each of the ends of the collector plate being located within one of the guard electrodes and the sensor further comprising an additional pair of insulator regions (44, 48) located within the guard electrodes to insulate the collector electrode from the guard electrodes, an ion chamber having a volume gradient across a length or width thereof; a pair of polarizing electrodes (32, 34) defining upper and lower portions of the ion chamber and providing a portion of a housing for the at least one GIC, the pair of polarizing electrodes being oriented with respect to one another to provide the volume gradient; a pair of insulator regions (46, 50) separating end portions of the polarizing electrodes from one another at opposite ends of the ion chamber; a pair of guard electrodes (40, 42) located within the insulator regions and configured to reduce the effect of leakage current on radiation dose measurement; a gas or liquid located within the ion chamber; and an electrode to detect ions generated within the gas or liquid when the at least one GIC is subjected to an ionizing radiation beam, the electrode to detect ions being a collector plate disposed between the pair of polarizing electrodes, each of the ends of the collector plate being located within one of the guard electrodes and the sensor further comprising an additional pair of insulator regions (44, 48) located within the guard electrodes to insulate the collector electrode from the guard electrodes, wherein the ion chamber has a surface area larger than a cross-sectional area of the ionizing radiation beam at the at least one GIC and the sensor encodes a location and amount of ionizing radiation provided by the radiation beam at the at least one GIC.