Abstract
Purpose: A 4‐Pi non‐coplanar converging (4PiNC) modality has been actively developed in our institution, in which the radiation beams are delivered along conic trajectories and rotate around the midline of a patient. The proposed design eliminates the potential gantry‐couch collision, a major concern of non‐coplanar beam delivery. This study introduces a method to implement the 4PiNC planning in the public‐domain treatment planning system (TPS) PLUNC. Methods: The cone angle of a 4PiNC delivery is defined as the angle between the cone edge and the transverse iso‐plane. The beam angle defines its relative position on the cone. We have mathematically proved that there is a one‐to‐one correspondence between a 4PiNC beam specification (cone and beam angle) and a LINAC beam specification (gantry and couch angle). Therefore, a graphic interface was written in PLUNC to design a 4PiNC RT plan using existing commissioned LINAC machines. The method was validated visually on a spherical phantom of 15cm radius with 12 beams evenly distributed on a cone, and with cone angle 40, ‐ 30, 20, ‐ 10 and 0 degree respectively. A 4PiNC RT plan was made for a prostate SBRT case with the afore‐mentioned 5 cones (20 beams on each cone) and was compared with the conventional five‐beam IMRT plan. Results: In the phantom study, the transverse planes at −3, 0 and 3 cm from the iso‐plane as well as the sagittal iso‐plane were examined; the beam separations and cone angles were consistent with those specified. The prostate study suggested that the OAR mean dose can be reduced by up to 44.5% by the 4PiNC RT plan with comparable PTV coverage. Conclusion: The RT planning for the proposed 4PiNC delivery system can be implemented in a TPS for conventional LINAC beams. This allows dosimetric investigation of the proposed system even before finalizing the hardware design. This work was partially supported by a DoD grant DoD W81XWH1010862
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