Preliminary experience of fractionated stereotactic radiosurgery with extend system of Gamma Knife

Raj Bisht, Shashank Kale, Gopishankar Nathanasabapathi, Pratik Kumar, Manmohan Singh, Deepak Agarwal, Sanjay Thulkar, Ajay Garg, Pramod Julka, Gaura Rath, Bhawani Sharma


Purpose: The purpose of this study is to present multisession stereotactic radiosurgery with initial experience using custom made extend system (ES) of Gamma Knife.

Methods: The ES is comprised of a carbon fiber frame also called extend frame, vacuum head rest cushion, patient surveillance unit and a configurable front piece with dental impression tray. The extend frame is a rigid connection between patient's head and patient positioning system (PPS) of Gamma Knife. A dental impression of patient was created and attached to the frontal piece of extend system. The treatment setup involves positioning the patient within the extend frame using patient specific headrest cushion and front piece. The reference patient’s head position was recorded through measurements of repositioning check tool (RCT) apertures using a high precision digital probe before computed tomography (CT) scan. The RCT measurements taken before treatment were compared with recorded reference position to ensure appropriate patient treatment position. Volumetric magnetic resonance (MR) scan was co-registered with stereotactic CT scan on Leksell Gamma plan. Fused MR to CT images on Gamma Plan was utilized to delineate regions of interest and prepare a precise treatment plan. The presented study includes positional reproducibility check and dosimetric evaluation of ten patients treated with ES.

Results: Forty-three fractions on ten patients with prescribed treatment format were delivered successfully. An average tumor volume of 11.26 cm3 (range, 340 mm3 to 59.12 cm3) was treated with ES. The mean tumor coverage of 91.91% (range, 90% to 95%) was able to achieve at 50% prescription isodose without compromising adjacent normal structure radiation dose tolerances. The mean inter-fraction positional variation of 0.69 mm influences an inherent strength of immobilization technique. Follow-up of seven patients at a median interval of 16 months (range, 9 months to 26 months) showed evidence of 100% radiographic control with improved clinical results.

Conclusion: Conjugative clinical outcome shows the efficacy of fractionation in various clinical indications.


Gamma Knife, Stereotactic Radiosurgery, Positional Accuracy

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