Author: Deepak Agrawal, Subhash Gupta, Shashanksharad Kale, Gopishankar Natanasabapathi, Manoj Phalak, Dhanabalan Rajasekaran, Surendra Kumar Saini, Subramani Vellaiyan 👨🔬
Affiliation: All India Institute of Medical Sciences (AIIMS), All India Institute of Medical Sciences 🌍
Purpose:
To evaluate planning strategy for uveal melanoma tumor (UM) in gamma knife stereotactic radiosurgery (GKSRS) using Lightning inverse planning software for treatment planning.
Methods:
Twenty uveal melanoma (UM) patients planned for Gamma Knife Stereotactic Radiosurgery (GKSRS) with the Leksell Gamma Knife Icon system were retrospectively analyzed. Ten had right-sided UM, and ten had left-sided UM. Eye fixation was achieved through chemical ophthalmoplegia (peribulbar injection of 5 mL 2% lignocaine, 5 mL 0.5% bupivacaine, and sodium hyaluronidase) and mechanical ophthalmoplegia (tying the three rectus muscles to the GK frame with 4-0 sutures). Temporary tarsorrhaphy was performed to prevent corneal exposure. MR imaging using the MP-RAGE sequence was done, and images were imported into Gamma Plan 11.1 for treatment planning and dose distribution. The Lightning Inverse Planning Software (LIPS) optimizer generated inverse plans based on user-defined objectives. The dose prescription aimed to maximize target coverage, while optimizing planning parameters like coverage (C), selectivity (S), gradient index (GI), beam-on time (BOT), and dose to organs at risk (OARs) such as the lens and optic nerve.
Results:
The target volume ranged from 2.12 cc. The average values for coverage (C), selectivity (S), and gradient index (GI) were 0.943, 0.77, and 3.28, respectively. For 16 cases, the dose prescription was 35 Gy, while the remaining 4 cases received doses between 28 Gy and 25 Gy. LIPS predicted the optimal isodose line for target coverage, improving upon the standard 50% isodose line. In earlier GK models, escalating the dose for UM was challenging due to factors like OAR dose limits, optimizing BOT, increased planning time, and maintaining eye apparatus integrity preventing deformation, which could lead to target displacement.
Conclusion:
In our UM cases, with the advent of LIPS in GKSRS, the efficiency in dose delivery to target has been significantly maximized.