Factors Influencing Long-Term Outcomes of Single-Session Gamma Knife Radiosurgery in Large-Volume Meningiomas >10 cc.

INTRODUCTION: Meningiomas are the most common primary intracranial tumour. Gamma knife radiosurgery (GKRS) is a frequently employed non-invasive method of treatment, with good remission rates and low morbidity in literature. However, the role of GKRS in the management of "large" meningiomas is unclear, with reported outcomes that vary by centre. We aimed to assess the factors that influence long-term outcomes following GKRS in meningiomas >10 cc in volume. METHODS: A retrospectively analysed all patients with meningiomas exceeding 10 cc in volume who underwent GKRS between January 2006 and December 2021 at the National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru. Demographic, clinical, radiological, and follow-up data were acquired, and factors associated with progression following GKRS were assessed. RESULTS: The cohort comprised 76 patients 29 males (38.2%) and 47 females (61.8%) with a mean age of 46.3 ± 11.02 years. Thirty-nine patients had been previously operated (51.3%). Meningiomas were most frequently located in the parasagittal region (26 tumours, 34.2%) and sphenopetroclival region (23 tumours, 30.3%), with mean lesion volume of 12.55 ± 5.22 cc, ranging 10.3 cc-25 cc. The mean dose administered to the tumour margin was 12.5 Gy ± 1.2 Gy (range 6-15 Gy). The median duration of clinical follow-up was 48 months, over which period radiological progression occurred in 14 cases (20%), with unchanged tumour volume in 20 cases (28.6%) and reduction in size of the tumour in 36 cases (51.4%). Progression-free survival after GKRS was 72% at 5 years, was significantly poorer among meningiomas with tumour volume >14 cc (log-rank test p = 0.045), tumours presenting with limb motor deficits (log-rank test p = 0.012), and tumours that underwent prior Simpson grade 3 or 4 excision (log-rank test p = 0.032). CONCLUSIONS: Meningiomas >10 cc in volume appear to display a high rate of progression and subsequent need for surgery following GKRS. Primary surgical resection, when not contraindicated, may be considered with GKRS serving an adjuvant role, especially in tumours exceeding 14 cc in volume, and presenting with limb motor deficits. Long-term clinical and radiological follow-up is essential following GKRS as the response of large meningiomas may be unpredictable.

Determination of Collimator Helmet Factors for Leksell Gamma Knife 4C Unit Using GAF Chromic EBT3 Film and ImageJ Software.

BACKGROUND: Measurement of Collimator helmet factors (CHF) is an important quality assurance procedure to be performed on Leksell Gamma Knife unit at regular interval to make sure that the interchangeable collimator helmet fit into the source channels without any positional inaccuracy which leads to major treatment error. The primary aim of this study is to measure the CHFs for Elekta Leksell Gamma knife 4C helmets using GafChromic EBT3 film and Image J software. METHODS: GafChromic EBT3 film, EPSON expression 10000 XL scanner and Image J analysis software was used for this study. The calibration curve of GafChromic EBT3 film was generated with known dose values for 14 mm collimator helmet using ImageJ software. The collimator helmet factor (CHF) for 4mm, 8mm and 14 mm collimator helmets were measured by normalizing dose rates of 4mm, 8mm and 14 mm to the dose rate of 18 mm collimator helmet using the previously generated calibration curve. The measured CHF was compared to Elekta reference value and previously published mean values. RESULTS: The measured CHFs were 0.896, 0.958, and 0.986 for 4mm, 8mm and 14mm collimators respectively. The percentage difference obtained was 1.7 %, 0.21 %, 0.1 % between measured values and reference values. CONCLUSION: The measurement of CHFs in LGK 4C unit using GafChromic EBT3 film and ImageJ software is a reliable method to verify the manufacturer quoted CHFs in routine quality assurance procedures.