Investigation of isotropic radiation of low energy X-ray intra-operative radiotherapy by MAGAT gel dosimeter

Purpose: Isotropy as a quality assurance aspect of intraoperative radiotherapy (IORT) needs to be evaluated accurately. There are some main problems associated with isotropy investigations by two dimensional dosimeters including limited positions and distances in which isotropy can be measured and long irradiation time needed for isotropy evaluation. In this study, isotropic radiation accuracy of spherical applicators of low energy X-ray IORT was estimated by the use of MAGAT gel as a three dimensional gel dosimeter and a specified IORT phantom. Methods: Designed IORT phantom was manufactured by multi-axis computer numerical control machine (CNC) using Plexiglas. To investigate isotropy, methacrylic acid, gelatin and tetrakis phosphonium chloride (MAGAT) gel dosimeters embedded in the phantom holes were irradiated with a 50 kV X-ray IORT device to 18 Gy at the surface of the vials. Then, relative dose deviations of output doses from their average were extracted from MRI images of the gel vials in different positions and distances from the 50-mm spherical applicator. Results: The percentages of relative deviations of output doses from the average value were less than 8% in all positions which are within the 15% acceptance limit of isotropy radiation. Moreover, a Pearson-moment correlation analysis showed a Pearson's r equal to 0.99-1 for different polar and azimuth angles representing isotropic radiation emission of X-ray IORT. Conclusion: Isotropy of IORT can be easily investigated using gel dosimeters by applying the produced phantom which solved the issues facing three-dimensional measurement of isotropic radiation of IORT X-ray source (XRS).

Automated summary

The isotropic radiation accuracy of low energy X-ray IORT spherical applicators was evaluated using a three-dimensional gel dosimeter. The study found that the relative dose deviations from the average were within the acceptance limit of isotropy radiation, demonstrating the isotropic radiation emission of X-ray IORT. The use of gel dosimeters and a specifically designed phantom effectively addressed the challenges in measuring the isotropic radiation of IORT X-ray sources.