Dosimetric characteristics of a thin bolus made with real time variable shape tungsten rubber for photon radiotherapy
Abstract In this study, we aim to clarify the dosimetric characteristics of a real time variable shape rubber containing tungsten (STR) as a thin bolus in 6-MV photon radiotherapy. The percentage depth doses (PDDs) and lateral dose profiles (irradiation field = 10 × 10 cm2) in the water-equivalent phantom were measured and compared between no bolus, a conventional 5-mm gel bolus, and 1-, 2-, and 3-mm STR boluses. The characteristics of the PDDs were evaluated according to relative doses at 1 mm depth (D1mm) and depth of maximum dose (dmax). The water-equivalent thicknesses of the STR boluses were determined by shifting the distance of the PDD’s build-up curve until it overlaid that with no bolus. The penumbra size and width of the 50% dose were evaluated using lateral dose profiles. The D1mm with no bolus, 5-mm gel bolus, and 1-, 2-, and 3-mm STR boluses were 47.6%, 91.5%, 86.6%, 89.3%, and 89.4%, respectively, and the respective dmax values were 15, 10, 12, 11, and 10 mm. The water-equivalent thicknesses of the 1-, 2-, and 3-mm STR boluses were 4.4, 4.9, and 5.1 mm, respectively. There were no differences for those in lateral dose profiles. The 1-mm-thick STR thin bolus shifted the depth dose profile by 4.4 mm and could be used as a customized bolus for photon radiotherapy.
