Red emission phosphor for real-time skin dosimeter for fluoroscopy and interventional radiology

There are no effective real-time direct skin dosimeters for interventional radiology. Such a scintillation dosimeter would be available if there was a suitable red emission phosphor in the medical x-ray range, since the silicon photodiode is a highly efficient device for red light. However, it is unknown whether there is a suitable red emission phosphor. The purpose of this study is to find a suitable red emission phosphor that can be used in x-ray dosimeters.

Five kinds of phosphors which emit red light when irradiated with electron beams or ultraviolet rays in practical devices were chosen. For the brightness measurement, phosphor was put into transparent plastic cells or coated onto plastic sheets. The phosphors were irradiated with medical range x-rays [60-120 kV(peak), maximum dose rate of 160 mGymin-1], and the emission was measured by a luminance meter. Several characteristics, such as brightness, dose rate dependence, tube voltage dependence, and brightness stability, were investigated.

The luminescence of Y V O₄:Eu, (Y,Gd,Eu) BO₃, and Y₂O₃:Eu significantly deteriorated by 5%-10% when irradiated with continuous 2 Gy x-rays. The 0.5MgF₂⋅3.5MgO⋅GeO₂:Mn phosphor did not emit enough. Only the Y₂O₂S:Eu,Sm phosphor had hardly any brightness deterioration, and it had a linear relationship so that the x-ray dose rate could be determined from the brightness with sufficient accuracy. For the tube voltage dependence of the Y₂O₂S:Eu,Sm phosphor, the brightness per unit dose rate with 120 kV(peak) x-rays was 30% higher than that with 60 kV(peak) x-rays.

Five kinds of phosphors were chosen as an x-ray scintillator for a real-time direct skin dosimeter. The Y V O₄:Eu, (Y,Gd,Eu)BO₃, and Y₂O₃:Eu phosphors had brightness deterioration caused by the x-rays. Only the Y₂O₂S:Eu,Sm phosphor had hardly any brightness deterioration, and it is a candidate for an x-ray scintillator for such a skin dosimeter.