Intraoperative radiotherapy using low-energy X rays：dosimetric characteristics and potential limitations in clinical application / 中华放射肿瘤学杂志

ABSTRACT

Objective To test intraoperative radiotherapy with mobile photon beam using the INTRABEAM system ( Germany) , and to analyze the dosimetric characteristics of low?energy photon beam using X?ray source and spherical applicators and explore its potential limitations in clinical application. Methods A special water phantom, a parallel?plate ionization chamber, and an electrometer were used to measure the depth dose rates and isotropy of dose distribution in x/y plane of X?ray source and different spherical applicators in the INTRABEAM system. Those data were then compared with the system data. Results For the X?ray source, the deviation of observed depth dose rate and isotropy in the x/y plane from the system data were-2.16%± 1. 36% and-1.9%~ 2. 1%, respectively. For applicators with different diameters, the deviation of observed depth dose rate, transfer coefficient, and isotropy in x/y plane from the system data were-10.0%~2. 3%,-8.9%~4. 2%, and-1.6%~2. 6%, respectively. Surface dose rate and dose gradient became larger with the decrease in the diameter of the spherical applicator. The measurement of depth dose rate and isotropy of X?ray source and spherical applicators showed good repeatability. The influencing factors for measurement accuracy included the positioning error of ionization chamber, energy response, noise current, and correction factor f ’ ( R ) . Conclusions This study reveals the dosimetric characteristics of the INTRABEAM system, verifies the accuracy of the system data, and obtains the data for clinical application and routine quality assurance. However, large dose gradient and small therapeutic range may limit its wide clinical application.