Sweeping-beam technique with electrons for large treatment areas as total skin irradiation : Dosimetric and technical aspects of a modified Stanford technique.

PURPOSE: Total skin electron beam therapy (TSEBT) is still a technical and therapeutic challenge today. Thus, we developed TSEBT using a sweeping-beam technique. METHODS: For treatment delivery, a linear accelerator Versa HD (ELEKTA, Stockholm, Sweden) with high-dose-rate electrons (HDRE) was used with a dose rate of 9000 MU/min. Dosimetry quality assurance was performed by multiple measurements with film dosimetry, 2D array, and Roos chamber. RESULTS: Clinical experience shows that treatment durations of 75 to 90 min are usual for the Stanford technique without using HDRE. With this new sweeping-beam irradiation technique, the total treatment time of a daily fraction could be reduced to 20 min while keeping over- and underdosing low. The treatment area is about 60 cmâ€¯× 200 cm and the dose distribution is uniform within 2% and 5% in vertical and horizontal directions, respectively. Initially, the electron energy of 6 MeV is reduced to 3.2 MeV by 1­cm polymethylmethacrylat (PMMA) scatter and the irradiation conditions of a source-surface distance (SSD) of 350 cm. The photon contamination drops to under 1%. CONCLUSION: These results show that the mean dose to total skin varies between 1.3 and 1.8 Gy. The sweeping-beam technique with electrons has a homogeneous dose distribution in connection with a short treatment time.