Local Failure and Reliability Analysis of Horizontal Struts in Deep Excavation Based on Redundancy Theory

The instability failure of many deep excavations supported by diaphragm walls (retaining piles) and horizontal struts is caused by the local failure of struts and the following large area chain effect. The lack of redundancy of struts is an important reason for the overall failure of supporting structures. In this paper, based on an actual excavation project, the numerical calculation model is established by Flac3D5.0, and the reliability of the supporting structure is analyzed based on the redundancy theory. The main conclusions are as follows: the redundancy of single support is large, and strut (6) (close to the middle of the excavation) is the most important. The redundancy is reduced due to continuous failure, and the redundancy is only 3.50 when strut (1)–(7) are all failed (half of the struts). The second row of the struts has the smallest redundancy, while the third row has the biggest redundancy.

A Prospective Study Assessing the Post-Prostatectomy Detection Rate of a Presumed Local Failure at mpMR with Either 64CuCl2 or 64CuPSMA PET/CT

Background: We aimed assess the detection rate (DR) of positron emission tomography/computed tomography with two novel tracers in patients referred for salvage radiotherapy (sRT) with a presumed local recurrence at multiparametric magnetic resonance (mpMR) after radical prostatectomy (RP). Methods: The present prospective study was conducted at a single institution between August 2017 and June 2020. Eligibility criteria were undetectable PSA after RP; subsequent biochemical recurrence (two consecutive PSA rises to 0.2 ng/mL or greater); a presumed local failure at mpMR; no distant metastases at 18F-fluorocholine PET/CT (CH/PET); no previous history of androgen deprivation therapy. Patients were offered both 64CuCl2 PET/CT (CU/PET) and 64Cu-PSMA PET/CT (PSMA/PET) before sRT. After image co-registration, PET findings were compared to mpMR ones in terms of DR and independent predictors of DR investigated at logistic regression. Results: A total of 62 patients with 72 nodules at mpMR were accrued. Compared to mpMR (DR = 100%, 95%CI: 94.9–100%), DRs were 47.2% (95%CI: 36.1–58.6%) and 54.4% (95%CI: 42.7–65.7%) for CU/PET and PSMA/PET, respectively (p < 0.001 for both). Both experimental PET/CT performed particularly poorly at PSA levels consistent with early sRT. Conclusions: The two novel radiotracers are inferior to mpMR in restaging the prostatic fossa for sRT planning purposes, particularly in the context of early salvage radiotherapy.

RADT-06. RADIOTHERAPY FOR BRAIN METASTASES FROM THYROID CANCER: A RETROSPECTIVE COHORT STUDY

PURPOSE/OBJECTIVE(S) Brain metastases from thyroid carcinoma are rare. Although stereotactic radiosurgery (SRS) is a standard of care for patients with brain metastases across many histologies, the current NCCN guidelines do not support a universal role for this modality in thyroid cancer. MATERIALS AND METHODS Thyroid cancer patients with brain metastases treated with radiotherapy at our institution from 2002-2020 were studied. Cumulative risk of local failure, distant intracranial failure and radiation necrosis were calculated using a competing risk of death analysis and censored at the last imaging follow-up. Overall survival was analyzed using Kaplan-Meier method. Stratified cox regression was used to study per-lesion outcomes. RESULTS We identified 34 patients with 203 treated brain metastases. 179 (88.2%) lesions were of differentiated histology; the remainder were anaplastic histology. Four patients received whole brain radiotherapy (WBRT) while 30 patients received SRS (SFED 22, interquartile (IQ) range 20-22). Of the patients receiving WBRT, one (25%) had anaplastic histology, and the median number of lesions was 15 (as compared to 2 for SRS). Median follow up among survivors was 32.3 months and median survival was 10.8 months. There were no observed failures (local or distant intracranial) observed at 1 year in the 24 metastases with anaplastic histology, although competing risk of death was high (91.7%). The 1 year cumulative incidences of local failure and distant intracranial failures were 9.8% (95CI 5.7%-13.9%) and 35.0% (95CI 29.0%-41.0%), respectively, in differentiated tumors. 6 (10.2%) of the distant intracranial failures were new cases of leptomeningeal disease. The 1 year risk of radiation necrosis was 15.5%. Of these cases, most were Grade 2 (57.1%); 3 (42.9%) were Grade 4 (there were no Grade 1 or 3 events). CONCLUSION In the largest known cohort of thyroid cancer brain metastasis patients, radiotherapy and SRS appear to be safe and effective treatment modalities.

RADT-01. COMPARATIVE STUDY OF LOCAL CONTROL FOR BRAIN METASTASIS BETWEEN PRE-FRAME AND POST-FRAME MRI METHODS OF GAMMA KNIFE STEREOTACTIC RADIOSURGERY

INTRODUCTION Gamma Knife radiosurgery (GKRS) is an established treatment modality in the management of brain metastasis (BM). The standard treatment flow includes frame placement followed by obtaining a post-frame MRI for planning. However, there has been a shift in practice towards using the pre-frame MRI method. It shortens the frame-wearing time while improving quality of imaging/targeting by decreasing artifacts by screws. However, no previous studies have compared the GKRS outcome between the pre- and post-frame MRI methods. METHODS 134 patients (61 pre-frame and 73 post-frame) with 307 BMs treated with first time GKRS were reviewed retrospectively. We defined local failure (LF) as ≥ 20% increase in maximum diameter (RECIST criteria). Kaplan-Meier and Gray’s method were used to estimate and compare cumulative incidence rate of LF between the groups; multivariable analysis for time-to-local failure (TTLF) was performed using Cox frailty model. The number of lesions was intrinsically modeled in frailty model. RESULTS There was no significant difference between the groups for background variables including age, gender, primary cancer, performance status, and number of lesions. Post-frame group had significantly smaller tumors at baseline (p=0.004). The cumulative incidence rates of LF for pre- vs post-frame groups were 1.6% vs 5.5% at 6 month, 6.9% vs 9.9% at 12 month, and 10.4% vs 17.4% at 24 month, respectively, without significant differences (p=0.84). Using multivariate frailty Cox model adjusting for age, gender, and lesion size, extracranial metastasis (HR 4.13, 95%CI 1.48‒11.57, p=0.007) was the significant prognostic factor for TTLF, while the frame type was not significant (p=0.46). CONCLUSIONS This is the first report comparing the GKRS outcome of pre- and post-frame MRI methods. The results indicated that pre-frame MRI method conveys a comparable local control for BM while maintaining practical benefits such as shortened frame-wearing time, less-artifact imaging, and longer preparation time available for planning.

Dynamical Recovery of Complex Networks under a Localised Attack

In real systems, some damaged nodes can spontaneously become active again when recovered from themselves or their active neighbours. However, the spontaneous dynamical recovery of complex networks that suffer a local failure has not yet been taken into consideration. To model this recovery process, we develop a framework to study the resilience behaviours of the network under a localised attack (LA). Since the nodes’ state within the network affects the subsequent dynamic evolution, we study the dynamic behaviours of local failure propagation and node recoveries based on this memory characteristic. It can be found that the fraction of active nodes switches back and forth between high network activity and low network activity, which leads to the spontaneous emergence of phase-flipping phenomena. These behaviours can be found in a random regular network, Erdős-Rényi network and Scale-free network, which shows that these three types of networks have the same or different resilience behaviours under an LA and random attack. These results will be helpful for studying the spontaneous recovery real systems under an LA. Our work provides insight into understanding the recovery process and a protection strategy of various complex systems from the perspective of damaged memory.

Gamma Knife versus Frameless Linear Accelerator Based Stereotactic Radiosurgery for Brain Metastases: Clinical Outcomes and Factors Associated with Local Failure and Radiation Necrosis

BackgroundSingle-fraction stereotactic radiosurgery (SF-SRS) for the treatment of brain metastases can be delivered with either a Gamma-Knife platform (GK-SRS) or with a frameless linear accelerator (LA-SRS) which vary based on patterns of prescribing, patient setup and radiation delivery. Whether these differences affect clinical outcomes is unknown. MethodsPatients treated for metastatic brain cancer treated with SF-SRS from 2014-2020 were retrospectively reviewed and clinical outcomes were recorded on a per lesion basis. Covariates between groups were compared using a Chi-square analysis for dichotomous variables and t-test for continuous variables. Median follow up was calculated using the reverse Kaplan Meier (KM) method. Primary endpoints of local failure (LF) and symptomatic radiation necrosis (RN) were estimated using the KM method with salvage WBRT used as a censoring event. Outcome estimates were compared using the log-rank test. Multivariate analysis (MVA) and Cox proportional hazards modeling were used for statistical analyses. Propensity score (PS) adjustments were used to reduce the effects confounding variables.ResultsOverall, 119 patients with 287 lesions were included for analysis which included 57 patients (127 lesions) treated with LA-SRS compared to 62 patients (160 lesions) treated with GK-SRS. On both multivariate and univariate analysis, there was no statistically significant differences between GK-SRS and LA-SRS for LF, RN, or the combined endpoint of either LF or RN (multivariate p-value=0.17).ConclusionsIn our retrospective cohort, we found no statistically significant differences in the incidence of RN or LF in patients treated with GK-SRS when compared to LA-SRS.Trial Registration: Retrospectively registered