Technical note: Enhanced radiosurgical planning for cavernous sinus tumors using T1 SPACE sequences with Motion-Sensitized Driven Equilibrium (MSDE)

Background and Objective: Radiosurgery can serve as a primary, adjuvant, or salvage treatment modality for cavernous sinus tumors (CST), providing high tumor control. However, particularly with cavernous sinus expansion, there may be insufficient distance from the optic apparatus to perform radiosurgery safely. The internal carotid artery adjacent to the distal dural ring (ICAddr), when enhancing similarly to the CST, can be difficult to delineate, and can lead to over-contouring of target volume near the optic nerve and therefore increasing the risk of radiation-induced optic toxicity. To evaluate the efficacy and safety of 3D T1-weighted Turbo Spin-Echo (TSE) MR sequence with the Motion-Sensitized Driven Equilibrium (MSDE) technique in accurately delineating the internal carotid artery adjacent to the distal dural ring (ICAddr) to minimize the risk of radiation-induced optic toxicity during radiosurgery for cavernous sinus tumors (CST). Methods: Nine patients were treated for CST with Gamma Knife radiosurgery from 2021 to 2023, utilizing a 3D T1-weighted Turbo Spin-Echo (TSE) MR sequence with the Motion-Sensitized Driven Equilibrium (MSDE) technique. Improved delineation of the ICAddr from the lesion facilitated precise dosimetry near the optic nerve. Results: At a median follow-up of 15 months, all patients demonstrated stable disease with no reported tumor progression. The use of the T1-weighted TSE MR sequence with MSDE significantly improved the delineation of the ICAddr from the cavernous sinus tumors. Only one patient experienced a transient episode of diplopia. No additional visual deficits were reported. Conclusion: The use of T1 SPACE sequence has enhanced the radiosurgical planning process for CST, allowing for more precise contouring of the lesion near the ICAddr and optic nerve and reducing radiation dose to the ipsilateral optic nerve. Integration of these techniques into standard practice may offer significant benefits for the radiosurgical management of CST.