Implementation of Linac-based VMAT total body irradiation technique on Elekta platform using surface-guided radiation...

To present an optimal workflow using a rotatable tabletop and a surface guided radiation therapy (SGRT) system for volumetric modulated arc therapy (VMAT) based total-body irradiation (TBI).

Twenty patients having received either 2 Gy, 8 Gy, or 12 Gy in 2 Gy per fraction were included. They were immobilized using a vacuum cushion and a three-points mask and positioned on a rotatable tabletop. VMAT treatment plans were performed on Monaco 6.1 (Elekta LTD, Stockholm) treatment planning system and then perturbed by applying shifts of 5mm on the isocenters coordinates to evaluate the robustness. Patients were treated on a Synergy or a VersaHD (Elekta LTD, Stockholm) Linac. Pretreatment positioning was performed either with cone-beam CT images combined with surface guided radiation therapy (SGRT) or with SGRT only. During treatment, intra-fraction motion was controlled with SGRT. Dosimetric data, robustness results and sessions duration were collected.

In terms of PTV coverage and lung-sparing, all plans met the requirements of the most recent recommendations. The use of 20-30 cm distances between isocenters, and a 90° collimator rotation, enabled to obtain a linear dose gradient between two consecutive beams, which ensured sufficient robustness against 5 mm shifts in isocenter coordinates in all directions. With an average duration of 1 h ± 12 min between the first and last beams, the first sessions were comparable in length to the extended source-to-skin distance technique.

Thanks to the rotatable tabletop and to the SGRT system, accurate and secured VMAT-based TBI treatments were performed within a reasonable timeframe, while ensuring patient comfort.