Enhancing total skin electron therapy: Introducing rotational technique and in-house-built flattening filter

Purpose To implement and commission a rotational Total Skin Electron Therapy (TSET) technique using high-dose-rate electron (HDRE) beams on an Elekta VersaHD linac and a custom-made flattening filter (FF), with the aim of improving delivery efficiency and dose uniformity. Methods Two HDRE beams (6 and 8 MeV) were characterized at an extended source-to-skin distance (SSD = 490 cm) using EBT3 film dosimetry. A customized FF was designed to optimize field uniformity in both vertical and horizontal directions. Percentage depth dose (PDD) and profile measurements were acquired in static and rotational setups. Monte Carlo simulations with EGSnrc/BEAMnrc and DOSXYZnrc were used to model the linac head and validated against measurements. Output ratios (ORs) were measured on a phantom to estimate the monitor units needed for rotational delivery. End-to-end (E2E) testing with an Alderson-Rando phantom and in vivo dosimetry on the first 50 patients were performed to assess dose uniformity and reproducibility. Results The custom FF significantly improved field flatness. Measured surface doses per 1000 MU were 82 cGy (HDRE1) and 106 cGy (HDRE2), with ORs of 0.52 and 0.56, respectively. The rotational technique allowed dose rates of 12.8–17.9 cGy/min and treatment times of 6–8 min. PDDs from Monte Carlo simulations matched measurements. E2E and in vivo dosimetry confirmed high uniformity and <1 % variability. In vivo dosimetry confirmed adequate surface dose coverage and intra-patient consistency. Conclusions The rotational TSET technique using HDRE beams on a VersaHD linac with a custom FF is feasible, reproducible, and dosimetrically robust, representing a valid alternative to conventional dual-field approaches.