Multilevel security and concurrency control for distributed computer systems

Multilevel security deals with the problem of controlling the flow of classified information. We present multilevel information flow control mechanisms for distributed systems that allow concurrent accesses to shared data. In a distributed computing environment, the different sites communicate through message passing. Our security mechanisms check the security of information flows caused by computations within individual sites as well as ones caused by communications among the sites. The correct behavior of the security mechanisms cannot be guaranteed if the allowed concurrency is left uncontrolled in the system. We present concurrency control mechanisms for the security mechanisms. In the presence of such concurrency control mechanisms, the consistency of the security data, which the security mechanisms rely upon, is preserved. Finally, we also present schemes to increase the efficiency and the precision of the security mechanisms

Multilevel security and concurrency control for distributed computer systems

Multilevel security deals with the problem of controlling the flow of classified information. We present multilevel information flow control mechanisms for distributed systems that allow concurrent accesses to shared data. In a distributed computing environment, the different sites communicate through message passing. Our security mechanisms check the security of information flows caused by computations within individual sites as well as ones caused by communications among the sites. The correct behavior of the security mechanisms cannot be guaranteed if the allowed concurrency is left uncontrolled in the system. We present concurrency control mechanisms for the security mechanisms. In the presence of such concurrency control mechanisms, the consistency of the security data, which the security mechanisms rely upon, is preserved. Finally, we also present schemes to increase the efficiency and the precision of the security mechanisms.</p

68Ga-PSMA PET/CT in early relapsed prostate cancer patients after radical therapy

Abstract Biochemical recurrence (BCR) of prostate cancer (PCa) occurs in about 25% of patients treated with radical prostatectomy (RP) and up to 45% in patients who receive external beam radiotherapy (RT). Early diagnosis of PCa recurrence is of high importance for successful salvage therapy. The aim of the present study is to analyze the efficacy of 68 Ga-PSMA PET/CT in detecting the presence of local and/or systemic disease in patients with a history of PCa who have BCR. A total of 52 PCa patients with BCR referred for 68 Ga-PSMA PET/CT were recruited from the American University of Beirut Medical Center between November 2017 and December 2019. We compared the performance of PSMA PET/CT to the results and clinical factors based on follow up: PSA, PSA kinetics, primary treatment, and Gleason score. The relationship between the PET/CT findings and clinical indicators of disease were assessed by univariate and multivariate logistic regression. From a total of 52 patients, 34 (65.4%) had positive PSMA-PET/CT scans. Among those, 8/34 (23.5%) received primary RT. For all patients with a positive PSMA-PET: the detection rate was 2/4 (50%) for PSA < 0.2, 5/10 (50%) for PSA 0.2–0.49, 3/6 (50%) for PSA 0.5–0.99, 6/12 (50%) for PSA 1–1.99, 8/9 (88.9%) for PSA 2–3.99, and 10/11 (90.9%) for PSA 4–10. PSMA-PET/CT positivity was significantly associated with PSA level at time of PET scan, PSA doubling time, Gleason score and TNM staging. However, it did not show a significant correlation with radiotherapy as primary treatment, ongoing androgen deprivation therapy (ADT), time to relapse, and initial PSA before therapy. In our single center prospective trial, 68 Ga-PSMA PET/CT successfully detected the recurrence of PCa in patients with BCR. Scan positivity was significantly associated with PSA level at time of PET scan, PSA doubling time, Gleason score, and TNM staging. PSMA- PET/CT is a highly promising modality in the work up of patients with PCa in the setting of BCR for earlier detection of disease recurrence