On the stability of Leksell Vantage stereotactic head frame fixation in Gamma Knife radiosurgery: a study based on cone-beam computed tomography imaging and the High Definition Motion Management system.

OBJECTIVE: The authors' objective was to investigate the stability of the newly introduced Vantage stereotactic frame fixation in single-fraction Gamma Knife radiosurgery. METHODS: A total of 255 patients were included in this work and treated with the Vantage frame and Leksell Gamma Knife (LGK) Icon equipped with cone-beam computed tomography (CBCT) imaging. After the frame was mounted on the patient's head, a CT scan was acquired. After the patient was positioned on the couch of LGK, CBCT was acquired to verify the target position before treatment delivery. A second CBCT examination was acquired after treatment delivery to assess intrafractional motion. During treatment delivery, the High Definition Motion Management (HDMM) system was enabled to track a marker on the nose tip of the patient as a surrogate of intracranial motion. The stability of the Vantage frame was deconstructed into two parts: 1) motion between CT and the first CBCT prior to treatment delivery (CT-CBCT1), and 2) motion between CBCT procedures during treatment delivery (CBCT1-CBCT2). Transformation between CT and CBCT1 was given by Leksell GammaPlan, whereas transformation between CBCT1 and CBCT2 required mathematical processing of the transformation and coregistration matrices in the source files. RESULTS: The average CT-CBCT1 displacement vector was 0.31 mm, with a range as great as 1.09 mm, and 89% and 97% of cases were within 0.5 mm and 0.7 mm, respectively. The CBCT1-CBCT2 displacement vectors averaged at 0.09 mm, with 97% of cases being within 0.2 mm. Spatial shift in the posterior direction was evident, with 94% of cases demonstrating this trend and averaging 0.05 mm. This was attributed to increased pressure on the posterior fixation pins. The HDMM displacement vectors presented larger values with an average of 0.4 mm and a range as great as 1.6 mm, and 98% of cases were within 1.0 mm. The correlation between CBCT1-CBCT2 and HDMM displacements was weak, which was attributed to the high stability of the Vantage frame and consequently small target displacements coupled with the sensitivity of HDMM to face mimics. CONCLUSIONS: This work demonstrated that the Vantage frame possess the same degree of submillimeter stability as the well-established Leksell Coordinate Frame G (G-frame). Displacements between CT and CBCT1 were 3 times higher than between CBCT1 and CBCT2. A suggested HDMM threshold of 1.2 mm ensures a target accuracy within 0.2 mm in Vantage frame treatments.

Adaptive hypofractionated gamma knife radiosurgery in the acute management of large thymic carcinoma brain metastases.

BACKGROUND: Brain metastases often lead to serious neurological impairment and life threatening states. Their acute management remains complex, particularly in the case of rare malignancies with aggressive evolution. In large single lesions, open surgery followed by radiation to the surgical cavity is widely regarded as the best approach; yet in many cases, microsurgery is not feasible due to the lesion's critical location and/or the number of brain metastases present. We report the effects of adaptive hypofractionated gamma knife radiosurgery in the acute management of critically located thymic carcinoma metastases. CASE DESCRIPTION: A 50-year-old male with metastatic thymic carcinoma was treated with radiosurgery for two large supratentorial brain metastases (M3 and M4) adjacent to eloquent areas and one smaller cerebellar metastasis (M2). M3 and M4 were treated with adaptive hypofractionated gamma knife radiosurgery, showing a dramatic volume reduction 4 weeks after treatment completion without radiation-induced side effects. Thirteen months later, two new small, threatening supratentorial lesions (M5-M6) were treated with the same technique. Interestingly, M2 (treated with standard single fraction) and M5-M6 developed local adverse radiation events. The patient's general and neurological status remained next to normal by the time of paper submission. CONCLUSION: The application of adaptive hypofractionated radiosurgery in this acute setting proved effective in terms of rapid tumor ablation, with salvage of neurological functionality and limited toxicity. We have called the overall procedure rapid rescue radiosurgery (RRR). A systematic study of past and ongoing RRR-treatments is warranted and in progress.

Salvage gamma knife radiosurgery in the management of dysembryoplastic neuroepithelial tumors: Long-term outcome in a single-institution case series.

BACKGROUND: Dysembryoplastic neuroepithelial tumors (DNT/DNET) are rare epileptogenic tumors. Microsurgery remains the best treatment option, although case reports exist on the use of gamma knife radiosurgery (GKRS) in selected cases. We investigated the long-term outcome of GKRS-treated DNTs at our institution in the context of current diagnostic and treatment options. CASE DESCRIPTIONS: We conducted a retrospective review of three consecutive adult patients (≥18 years) treated with salvage GKRS between 2002 and 2010 at Karolinska University Hospital, Stockholm, Sweden. The case series was supplemented by a review of current literature. A 20-year-old male underwent subtotal resection (STR) in 1997 and 2002 of DNT resulting in temporary control of intractable epilepsy despite antiepileptic drug treatment (AED). Long-term seizure control was obtained after GKRS of two separate residual DNT components along the surgical margin (2005 and 2010). A 27-year-old male undergoing gross total resection of the contrast-enhancing portion of a DNT (1999) resulted in temporary control of intractable epilepsy despite AEDs; lasting clinical control of seizures was achieved in 2002 after GKRS of a small, recurrent DNT component. A 28-year-old male underwent STR of DNT (1994 and 2004) resulting in temporary control of intractable epilepsy. Lasting seizure control was gained after GKRS of a residual tumor (2005). CONCLUSION: GKRS as performed in our series was effective in terms of tumor and seizure control. No adverse radiation effects were recorded. Prospective studies are warranted to establish the role of GKRS in the treatment of DNTs.