First clinical implementation of dynamic tumor-tracking volumetric modulated arc therapy with a gimbal-mounted linac: short delivery time and high precision.

Dynamic tumor tracking (DTT) is an effective respiratory motion management strategy for thoracic and abdominal tumors and enables treatment delivery under free breathing using gimbal-mounted linac, without requiring breath-holding. To date, however, clinical implementations have used three-dimensional conformal radiotherapy (3D-CRT) or fixed-field intensity-modulated radiotherapy (IMRT), and integration with volumetric modulated arc therapy (VMAT) has been anticipated to shorten treatment time while improving dose distribution. This short communication reports the first clinical implementation of stereotactic body radiotherapy with DTT-VMAT using a novel gimbal-mounted linac. Planned treatment using DTT-VMAT for liver tumor over five treatment days was delivered successfully, with a mean treatment time of 23.2 min (range, 12-33 min), shorter than previously reported gimbal-based DTT with 3D-CRT or fixed-field IMRT. The average 3D tracking error was 2.4 ± 1.8 mm overall, comprising 0.3 ± 1.0 mm laterally, -1.5 ± 2.2 mm longitudinally and - 0.1 ± 1.0 mm vertically, maintaining tracking performance comparable to earlier systems. No updates to the four-dimensional model were required during beam delivery. This introduction of novel gimbaled-based DTT-VMAT approach is advantageous among available respiratory motion management techniques, as it shortens treatment time, mitigates baseline drift and improves patient compliance.