Dosimetric investigation of a rotating gamma ray system.

Background. Radiosurgery has become an important treatment alternative to surgery for a variety of intracranial lesions. All commercially available systems use convergent beam techniques, but they differ in their treatment delivery methods depending on the machine design and workspace.Purpose. The aim of this work is to investigate a new design for a gamma ray system developed for both intra and extra-cranial stereotactic body radiation therapy (SBRT).Methods. Monte Carlo simulations have been conducted to evaluate rotational radiation delivery using Cobalt-60 gamma beams as compared to linac beams with higher energies. A rotating gamma ray system (RGS), has been modeled using the MCBEAM Monte Carlo code. Treatment plans have been generated utilizing MCPLAN, which is an in-house Monte Carlo treatment planning system. Dosimetric differences between RGS Cobalt-60 beams and Robotic arm linac (RAL) 6 MV beams have been compared in a lung phantom and for previously treated SBRT patients.Results. Results showed that the need for high-energy photon beams decreases with rotational delivery treatments. Cobalt-60 beams could provide a reasonable compromise between beam penetration and penumbra characteristics for lung SBRT applications. The proper combination of available collimator cone sizes and various oblique beam angles allows RGS to shape the isodose lines effectively to match the target volume. The treatment plan quality for RGS has been comparable to that of RAL for both intra- and extra cranial cases. Intensity modulated arcs are feasible with RGS and can add more planning capabilities.Conclusions. The rotating design of the RGS can be of clinical benefit for stereotactic radiation therapy treating cranial cases plus the added ability of treating extra-cranial cases.