Stereotactic Radiosurgery with Gamma Knife in Recurrent Rathke's Cleft Cyst: Case Report and Literature Analysis.

Background: Rathke's cleft cyst is a benign expansive lesion of the sella turcica. If related to clinical disorders, the patient needs surgical treatment. Objective: To demonstrate the efficacy of radiosurgery in the treatment of relapse of Rathke's cleft cyst as an alternative to surgery. Methods and Material: The stereotactic radiosurgical treatment was performed at the Gamma Knife Center of the Niguarda Hospital in a patient with Rathke's cleft cyst subjected to two subsequent neurosurgical resections with early regrowth of the cyst. The cyst underwent radiosurgery with a prescription dose of 12 Gy at 50% (minimum dose 9.8, mean 17.3 and maximum 24.4). Results: Three years after stereotactic radiosurgical treatment the patient is asymptomatic and does not present disorders of the hypothalamic-pituitary axis or further visual alterations. The control MRI shows a reduction of the cyst's volume. Conclusions: Stereotactic radiosurgery resulted in a reduction of the cyst's volume and avoided further recourse to surgery.

Gamma Knife Radiosurgery for Treatment of Brain Metastases during the COVID-19 Outbreak.

INTRODUCTION: The WHO declared 2019 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) a public health emergency of international concern. The National and Regional Health System has been reorganized, and many oncological patients died during this period or had to interrupt their therapies. This study summarizes a single-centre experience, during the COVID-19 period in Italy, in the treatment of brain metastases with Gamma Knife stereotactic radiosurgery (GKRS). METHODS: We retrospectively analysed our series of patients with brain metastases who underwent GKRS at the Niguarda Hospital from February 24 to April 24, 2020. RESULTS: We treated 30 patients with 66 brain metastases. A total of 22 patients came from home and 8 patients were admitted to the emergency room for urgent neurological symptoms. Duration of stay was limited to 0-1 day in 17 patients. We chose to treat a cluster of 9 patients, whose greater lesion exceeded 10 cm3, with 2-stage modality GKRS to minimize tumour recurrence and radiation necrosis. CONCLUSION: Due to the COVID-19 pandemic, the whole world is at a critical crossroads about the use of health care resources. During the COVID-19 outbreak, the deferral of diagnostic and therapeutic procedures and a work backlog in every medical specialty are the natural consequences of reservation of resources for COVID-19 patients. GKRS improved symptoms and reduced the need for open surgeries, allowing many patients to continue their therapeutic path and sparing beds in ICUs. Neurosurgeons have to take into account the availability of stereotactic radiosurgery to reduce hospital stay, conciliating safety for patients and operators with the request for health care coming from the oncological patients and their families.

FLUKA Monte Carlo simulation for the Leksell Gamma Knife Perfexion radiosurgery system: homogeneous media.

The purpose of this work is to investigate the capability of the FLUKA Monte Carlo (MC) code to simulate the Elekta Leksell Gamma Knife Perfexion (LGK-PFX) and reproduce the Treatment Planning System (TPS) Leksell GammaPlan version 8.2 (LGP) dose calculations for the case of a water equivalent phantom target. Thanks to the collaboration with Elekta Instruments AB, the collimation system geometry, the source positions and all the involved material have been simulated in detail. The relative linear dose distribution along the three coordinate axes, for each collimator size, and the Relative Output Factors (ROF) have been investigated. The simulation has been validated comparing simulated linear dose profiles with measurements performed with EBT radiochromic films. The acceptance criterion between experimental data and FLUKA results is based on the gamma index (GI) method. The FLUKA MC calculation for the ROF provided the values of 0.920 for the 8 mm collimators and 0.800 for the 4 mm collimators. These values are in good agreement with the Elekta reference data of 0.924 and 0.805 respectively. The percentage difference between calculated and reference values for the ROF is under 1% and within the FLUKA uncertainty. Also the simulated relative dose profiles show a good agreement with the LGP calculation expressed by means of the gamma index method. This established accuracy proves that FLUKA is a suitable and powerful tool in order to reproduce successfully the LGP calculations for the homogeneous media.

Preparation of "high specific activity" radiochemical forms of vanadium, manganese and thallium for metallo-toxicological studies.

In this paper are presented the production methods for very "high specific activity" radionuclides (HSA-RN) of vanadium, manganese and thallium which have been developed in our laboratories for labelling different chemical forms of these elements present in the echo-systems in ultra-trace amounts, for metallo-toxicological and bio-kinetic studies. Use was made of both cyclotron and thermal nuclear reactor. If the nuclear reaction product has atomic number different from irradiated target, it is possible separating the radioactive nuclide from irradiated target, without addition of isotopic carrier. This kind of radionuclide is named No Carrier Added, NCA, and his specific activity, As is very high and can reach values close to the theoretical Carrier Free one, CF. The experimental determination of specific activity, chemical and radiochemical purities is mandatory for all these kinds of applications.