Abstract
Background: Conventional electron beam radiotherapy used for treating superficial cancer tumors suffers from the disadvantage of low skin sparing effect. Furthermore, increasing electron energy for treating deeper-seated tumors leads to significant increase of skin dose. To overcome this, various grids are recommended for electron beam radiotherapy of subcutaneous tumors. However, appropriate grids are required to be designed for decreasing skin dose while delivering uniform high doses to deep-seated superficial tumors. Our goal was to design, examine and propose appropriate grid(s) for optimum electron beam radiotherapy of subcutaneous tumors with the best skin sparing with 6 and 18 MeV energies.Materials and Methods: Relevant dosimetric characteristics were determined and analyzed for five grids manufactured from dry lead having various cavity diameters (1.5, 2.0, 2.5, 3.0, 3.5 cm) and shielded areas (0.3, 0.4, 0.5, 0.6, 0.7 cm) among the cavities but the same fraction of cavity/open (68%) and shielded/closed (38%) areas under the grid plates. Isodose distributions and dose profiles resulted from the grids were investigated using EDR2 films and MATLAB software. Results: The grids with 2 and 2.5 cm diameter cavities and 0.4 and 0.5 cm shielded areas were the most appropriate grids for 6 and 18 MeV radiotherapy, respectively. With these grids, the 100% PDDs (percentage depth doses) located at 1.25 and 2.5 cm for an open filed (without the grids) were moved down to 1.87 and 5.4 cm for 6 and 18 MeV energies, respectively. Furthermore, the proposed grids provided the least peak to valley dose variations hence the most uniform doses delivered at their relevant depths of treatment. Conclusions: To decrease the skin dose in 6 and 18 MeV electron beam radiotherapy of superficial subcutaneous tumors, various home-made grids were designed and investigated. The most appropriate grids (having 2 and 2.5 cm cavity diameters for 6 and 18 MeV, respectively) provided the optimum dose delivery for superficial subcutaneous tumors locating around 1.5 and 5 cm depth for 6 and 18 MeV energies. Our comprehensive study provides reliable results that could be considered and developed more for a wider range of MeV electron grid therapies in routine clinical practices.