X radiation dosimetry in invasive cardiovascular studies

摘要

Invasive cardiovascular procedures use fluoroscopy and video fluoroscopy for long term and withseveral operational conditions that might overexpose patients ’ skin to X-ray causing deleterious damage asdeterministic effect. In invasive cardiologic studies, X-ray exposure time can be up to 150min, which obliges theprofessional to operate the equipment with optimised techniques. The expert must know the radiation dosemagnitude in order to minimize the risks. The objective of this work is to estimate skin surface Kerma distributionin invasive cardiovascular studies using thermoluminescent dosimeters (TLD) at normal and low automaticexposure techniques in different X-ray incidence angles using phantom, and compare the maximum skin entranceKerma with the air Kerma measured at skin level with ionizing chamber. Fifty TLD900 dosimeters were placed onthe surface of the acrylic phantom. Measurements were made using normal and low automatic exposure incineangioscopy equipment Toshiba Infinix at perpendicular to, and at oblique incidences of 45° left and right. TLmeasurements were made with a Harshaw 4000. Values of incident air Kerma at skin level measured in theQuality Control Program (QCP) according to requirements of Brazilian standards were compared to maximumskin entrance Kerma. From the technical data registered in the exams, one of the most frequent exposureconditions was 110kVp; 99mA, 2.3ms, pulse mode, 30fps, and 31cm intensifier diameter and 100cm sourceintensifier distance. Under these conditions we can graphically verify the dose distribution on the phantom surfacein different geometrical conditions. Under the above technical conditions, the skin entrance Kerma was measuredusing the ionizing chamber as protocol used in the routine Quality Control Program. The results with the ionizingchamber showed underestimated values when compared with the TLDs. It was possible to conclude thatthermoluminescent dosimetry, despite intrinsic operational difficulties, allows determining the absorbed dosedistribution on the surface skin with smaller uncertainties.