Monte Carlo simulation of photons backscattering from various thicknesses of lead layered over concrete for energies 0.25-20 MeV using FLUKA code.

There is an increased interest in determining the photon reflection coefficient for layered systems consisting of lead (Pb) and concrete. The generation of accurate reflection coefficient data has implications for many fields, especially radiation protection, industry, and radiotherapy room design. Therefore, this study aims to calculate the reflection coefficients of photons for various lead thicknesses covering the concrete. This new data for lead, layered over concrete, supports various applications, such as an improved design of the mazes used for radiotherapy rooms, which helps to reduce cost and space requirements. The FLUKA Monte Carlo code was used to calculate photon reflection coefficients for a concrete wall with different energies. The reflection coefficient was also calculated for a concrete wall covered by varying thicknesses of lead to study the effect of lining this metal on the concrete wall. The concrete's reflection coefficient data were compared to internationally published data and showed that Monte Carlo calculations differed significantly from some of the extrapolated data. The absorbed dose of backscattered photons for various thicknesses of lead covering the ordinary concrete has been tabulated as a function of the reflection angle. Also, the reflection coefficient as a function of the Pb thicknesses covering the ordinary concrete has been figured to study the dose reduction factor. The generation of accurate data for reflection coefficients is vital for many fields, especially for radiation protection and radiotherapy room design. The new data have been presented for lead layered over concrete in various applications, such as an improvement in the design of the mazes used for radiotherapy rooms, thereby reducing the cost and space requirements. In addition, the Monte Carlo method enables calculating the energy distribution of reflected photons, and these were shown for a range of angles.

Determination of the photon spectrum of a therapeutic linear accelerator near the maze entrance: Comparison of Monte Carlo modeling and measurements using scintillation detectors corrected for pulse pile-up.

PURPOSE: The determination of x-ray spectra near the maze entrance of linear accelerator (LINAC) rooms is challenging due to the pulsed nature of the LINAC source. Mathematical methods to account for pulse pile-up have been examined. These methods utilize the highly periodic pulsing structure of the LINAC, differing from the effects of high-intensity radioactive sources. METHODS: Sodium iodide (NaI) and plastic scintillation detectors were used to determine the energy spectra at different points near the maze entrance of a medical LINAC. Monte Carlo calculations of the energy distribution of scattered photons were used to simulate the energy spectrum at the maze entrance. The proposed algorithm uses the Monte Carlo code, FLUKA, to calculate a response function for both detectors. To determine the effects of the pile-up in the spectra, the Poisson distribution was used, employing the average number of photons per pulse (µ) interacting with the detector. The quantity, µ, was obtained from the ratio of the number of events detected to the number of pulses delivered. The energy spectra at various distances from the maze entrance were measured using NaI and plastic scintillation detectors. From these measurements, the values of µ were calculated, and the pile-up probability was determined. The FLUKA Monte Carlo code was used to calculate the spectrum at the maze entrance and the response matrices of the NaI and plastic scintillation detectors. The algorithm based on the Poisson distribution was applied to calculate the spectrum. RESULTS: The agreement between the calculated and measured spectra was within the first standard deviation of the variance expected in µ. This agreement confirms that photons at the maze entrance have energies between 30 and 240 keV for a maze with three turns, with an average energy of around 85 keV. After pile-up correction, the range of the pulse height distribution with the plastic scintillation detector, which has a low atomic number, was decreased (0 to 140 keV). In contrast, the range of the pulse height distribution with the NaI scintillation detector was closer to the photon spectrum (0 to 240 keV). CONCLUSIONS: The corrected spectrum demonstrates that using a FLUKA Monte Carlo code and an algorithm based on the Poisson distribution are effective methods in removing the distortion due to the pile-up in LINAC spectra when measuring with NaI and plastic scintillation detectors. The agreement between the corrected and measured spectra indicates that Monte Carlo modeling can accurately determine the spectrum of a LINAC machine at the maze entrance.

Systematic review and meta-analysis to compare outcomes between intermediate- and high-risk patients undergoing transcatheter aortic valve implantation.

Aims: Recent studies have reported non-inferior outcomes for transcatheter aortic valve implantation (TAVI) compared with surgical aortic valve replacement (SAVR) in intermediate-risk patients. However, a comparison of outcomes among TAVI patients depending upon the surgical risk score has not been performed in a large study. Our aim was to compare the outcomes of TAVI in low-, intermediate-, and high-risk patients, to ascertain if the morbidity and mortality is related to the patient's risk profile or the procedure itself. Methods and results: A thorough computer-based search was performed using Ovid MEDLINE, EMBASE, Google Scholar, and PubMed databases. We included original research studies reporting data on TAVI in the low-, intermediate-, and high-risk groups. Patients in intermediate-risk group were compared to the high-risk cohort for device success, mortality, and complications. A total of 2414 patients in the intermediate-risk group were compared with 1597 high-risk patients. On meta-analysis, intermediate-risk group demonstrated similar device success [odds ratio (OR) 1.29, 95% confidence interval (CI) 0.87-1.90, I2 = 0%, P = 0.2) but a lower 30-day mortality OR 0.54, 95% CI 0.34-0.86, I2 = 49%, P = 0.009). There was no difference in the incidence of stroke (OR 1.17, 95% CI 0.80-1.71, I2 = 36%, P = 0.42) or permanent pacemaker implantation between the two groups (OR 1.04, 95% CI 0.82-1.32, I2 = 41%, P = 0.74). Conclusion: Transcatheter aortic valve implantation in intermediate-risk patients carries a low mortality and high success. Incidence of pacemaker and stroke remains high in the lower risk group.

A meta analysis of current status of alcohol septal ablation and surgical myectomy for obstructive hypertrophic cardiomyopathy.

OBJECTIVE: Our objective was to perform an updated systematic review to compare the efficacy and short- and long-term mortality of surgical myectomy (SM) and alcohol septal ablation (ASA) by including most recent and largest cohort studies published in last few years. BACKGROUND: SM and ASA are the two invasive strategies used to relieve left ventricular outflow tract obstruction (LVOTO) in patients with drug refractory symptomatic hypertrophic cardiomyopathy (HCM). In the absence of a randomized trial, we tried to compare the pros and cons of the two procedures using a systematic review and meta-analysis. METHOD: A comprehensive search of three major databases was performed. We included original research studies comparing data on ASA and SM. Of 1,143 citations, 10 studies were included in the analysis. RESULTS: A total of 805 patients underwent ASA and 1,019 underwent SM. Patients undergoing SM were younger (MD 6.3, P = 0.0001) and had higher reduction in the LVOT gradient (MD -9.56, P = 0.05). However, there was similar resolution of class III and IV symptoms between the two groups (P = 0.56). There was no difference in sudden cardiac death (SCD) (P = 0.93), short-term (P = 0.36), long-term all cause (P = 0.27), and long-term cardiac mortality (P = 0.58). Patients undergoing ASA had higher incidence of post procedure device implantation (OR 3.09, P < 0.00001). CONCLUSION: No significant difference in symptom relief was noted between the two approaches. ASA was as safe a myectomy with regards to SCD, short-term, and long-term mortality. © 2015 Wiley Periodicals, Inc.

Rapid RBE-Weighted Proton Radiation Dosimetry Risk Assessment.

Proton therapy dose is affected by relative biological effectiveness differently than X-ray therapies. The current clinically accepted weighting factor is 1.1 at all positions along the depth-dose profile. However, the relative biological effectiveness correlates with the linear energy transfer, cell or tissue type, and the dose per fraction causing variation of relative biological effectiveness along the depth-dose profile. In this article, we present a simple relative biological effectiveness-weighted treatment planning risk assessment algorithm in 2-dimensions and compare the results with those derived using the standard relative biological effectiveness of 1.1. The isodose distribution profiles for beams were accomplished using matrices that represent coplanar intersecting beams. These matrices were combined and contoured using MATLAB to achieve the distribution of dose. There are some important differences in dose distribution between the dose profiles resulting from the use of relative biological effectiveness = 1.1 and the empirically derived depth-dependent values of relative biological effectiveness. Significant hot spots of up to twice the intended dose are indicated in some beam configurations. This simple and rapid risk analysis could quickly evaluate the safety of various dose delivery schema.