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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.

Treatment of meningioma in the posterior cranial fossa represents a formidable challenge for the neurosurgeon. Although surgical resection is the primary treatment option for posterior fossa meningiomas, there is an important risk of injury to neurovascular structures adjacent to the brainstem. Furthermore, residual or recurrent tumours following resection are not rare, in spite of recent advances in microsurgery and anaesthesiology, including intraoperative neurophysiological monitoring.

This work aims to construct a method to objectively evaluate CT image quality when new clinical protocol performances must be compared with a standard reference. We compare iterative reconstruction in the image space with filtered back projection reconstruction and accurately quantify the dose reduction. The comparison strategy accounts for both physical and clinical image qualities that are evaluated using a standard metric. The quasi-ideal observer metric is also explored to verify its reportedly high correlation with perceived image quality. Water or spatial resolution phantom images are used to characterise the physical image quality using the classic metrics in the Fourier domain by calculating the modulation transfer functions and noise power spectra (NPS). The clinical-image quality is evaluated with a 4-alternative forced-choice test. The human observers are asked to detect a positive image that contains a simulated lesion in a background image. Then, the same positive images are characterised with the quasi-ideal observer metric, which calculates the non-prewhitening matched filter signal-to-noise ratio (SNRNPWMF). Iterative reconstruction strongly reduces the image noise, but the NPS are slightly shifted to lower frequencies, which gives the images a coarse graininess. Compared with the reference FBP protocol for abdomen exams, the highest dose reduction is 40% if the standard metric is used and 30% if the SNRNPWMF metric is used. The detectability test results achieve a better correlation with SNRNPWMF than with the standard metric. The identified Fourier metric is a useful descriptor of human quality perception and can be used for future protocol optimisation.

OBJECTIVE To optimize a dual-energy computed tomographic protocol with sinogram-affirmed iterative reconstruction algorithms for improving small nodules detection. METHODS The raw data of a dual-energy computed tomographic arterial acquisition of a cirrhotic patient were reconstructed with a standard filtered back projection (B20f) and 3 iterative (I26, I30, I31) kernels with different strength (S3-S5). The 80-kilovolt (peak) (kVp) and the linear blended (DE_0.5) images (80-140 kVp) were analyzed. For each series, 8-subcentimeter low-contrast lesions were simulated within the liver. Four radiologists performed a detectability test and rated the image quality (5-point scales) in all images. RESULTS The sensitivity increased from 31% (B20f) to 87.5% with sinogram-affirmed iterative reconstruction S5 kernels without a difference between 80-kVp and DE_0.5 series (W test, P = 0.062). The highest image quality rating was 3.8 (B20 DE_0.5), without difference from DE_0.5 I30-S5 and I26-S3. CONCLUSIONS Iterative reconstructions increase the sensitivity for detecting abdominal lesions, even in the 80-kVp series. The kernel I30-S5 was considered the best.