Determination of patient-specific trajectory for biaxially rotational dynamic-radiation therapy using a new O-ring-shaped image guided radiotherapy system

Background and purpose

This study developed a trajectory search method for biaxially rotational dynamic-radiation therapy (BROAD-RT) using a new O-ring-shaped linac, aimed at identifying a patient-specific trajectory in a commercial treatment planning system. Subsequently, its efficacy in the treatment of pancreatic cancer was assessed.

Materials and methods

BROAD-RT is a beam delivery technique in which the gantry and O-ring are simultaneously rotated around two axes. A beam’s eye view-based structure map was generated, and the Dijkstra algorithm was then applied to explore the BROAD-RT for minimizing radiation doses to critical organs in RayStation. This procedure was evaluated in 10 patients with pancreatic cancer. For each patient, two different plans were created: volumetric modulated arc therapy (VMAT) plan with coplanar and BROAD-RT trajectory. The effects of different trajectories on the plan and dosimetric indices were assessed for each delivery technique.

Results

The mean modulation complexity score for VMAT (MCS_v) and aperture area (AA) (×10³ cm²) were 0.3 ± 0.0 and 24.8 ± 3.9 for the coplanar trajectory and 0.4 ± 0.1 and 35.2 ± 7.1 for the BROAD-RT trajectory, respectively, with both MCS_v (p = 5 × ${10}^{-5}$) and AA (p = 0.0002) values significantly higher for the BROAD-RT trajectory. Dose difference between the coplanar and BROAD-RT trajectories reduced the dose to the stomach and duodenum.

Conclusions

Our study conducted an automated search for patient-specific BROAD-RT trajectory using a new O-ring-shaped linac and implemented these trajectories in RayStation. Dose distributions were reduced in the intermediate-dose regions with BROAD-RT trajectory.