The Spectral Measurement of Scattered Radiation From a Clinical Linear Accelerator Using a CZT Detector

The study of the induced radioactivity following radiotherapy with high energy X-rays from medical linear accelerator. Patient equivalent phantom made of Polymethyl methacrylate (PMMA) of 30x30x27 cm size irradiated with 15 MV X-rays from Versa HD medical linear accelerator form Elekta. Induced radioactive and ambient dose rates were measured at 0.25, 0.5 and 1 m from beam center using GR1® spectrometry with Cadmium Zinc Telluride (CZT) detectors having energy resolution less than 2%. Spectrum analysis was performed using MultiSpect software. The measured spectrum showed 511 keV annihilation photons possibly as a result of positron emitter of which most likely candidates are 62Cu(T1/2: 9.7 min), 64Cu (T1/2: 12.7 h )  and 57Ni  (T1/2:  35.6 h) and a  peak at ≈ 1780 keV that could be attributed 28Al and 214Bi radioisotope. Ambient photon dose rates post radiotherapy treatment ranged 660 µGyh-1at o.5 m to 41 µGyh-1at 1 m. These values agree well with the results presented in the literature. Keywords: Radiotherapy; Activation Products; Gamma spectrometry; Occupational exposure; Medical Linear Accelerator. DOI: 10.7176/ALST/83-05 Publication date: November 30th 2020

An evolutionary inspection game with labour unions on small-world networks

We study an evolutionary inspection game where agents can chose between working and shirking. The evolutionary process is staged on a small-world network, through which agents compare their incomes and, based on the outcome, decide which strategy to adopt. Moreover, we introduce union members that have certain privileges, of which the extent depends on the bargaining power of the union. We determine how the union affects the overall performance of the firm that employs the agents, and what are its influences on the employees. We find that, depending on its bargaining power, the union has significant leverage to deteriorate the productivity of a firm, and consequently also to lower the long-run benefits of the employees

Production of actinium-225 from a (n,p) reaction: Feasibility and pre-design studies

Actinium-225 is used in nuclear medicine for the treatment of malignant tumours. It can be applied to produce Bi-213 in a reusable generator or can be used alone as an agent for radiation therapy, in particular for targeted alpha therapy. However, the availability of Ac-225 for worldwide use, particularly in low- and middle-income countries, is limited. We present a feasibility study employing GATE, an open-source Monte Carlo simulation toolkit, on the production of Ac-225 from a neutron generator. This work suggests that a design consisting of three concentric cylinders, the innermost a Cf-252 neutron source, the middle nickel cylinder acting as a proton-producing target and the outer cylinder a RaCl2 target may provide a feasible design outline for an Ac-225 generator

Radiation dose homogeneity and critical organs in radiotherapy treatment of prostate cancer

Present study compares two different 3D radiotherapy techniques: three-dimensional conformal radiotherapy (3D-CRT) and 3D external-beam radiation dose fields from computerized treatment plans, produced for 30 prostate cancer patients. All of the patients were the subject of treatment at the National Cancer Institute in Egypt. Evaluation was made of dose homogeneity within the target volume and the dose to critical organs (organs at risk, OAR). The plans were based on CT scans, all for cases of localized prostate cancer (all stage T2N0M0), with the CT scans transferred to the treatment planning systems. Comparison of the two different 3D radiation techniques was made in terms of isodose distributions and dose-volume histograms. The percentage of the planning target volume receiving 95% (V95) and 107% (V107) of the prescribed dose were obtained. For the 3D-CRT technique, the mean values for these were respectively 90.6% and 5.7% while for the other 3D technique they were 94.9% and 3.8%. In examining the dose received by the OAR, use of the 3D-CRT technique was found to provide the preferred dose distribution, with much greater sparing of the bladder, rectum and head of both femora. For the rectum the mean V70, V75 and D95 values (the latter referring to doses to 95% of the treatment volume) for the 3D-CRT technique were 35.5%, 32.2% and 34% while for the other 3D technique these were 8.4%, 0.2% and 12% respectively. For the bladder, the mean V40 and V65 values obtained using the 3D-CRT technique were 80.8% and 74.9% while for the alternative 3D technique they were 20.4% and 17% respectively. Thus for the particular cohort, the 3D-CRT technique provided superior target coverage and reduction of dose to the OAR

Sensing mammographic density using single-sided portable Nuclear Magnetic Resonance

This research paper presents a quantitative approach to sensing mammographic density (MD) using single-sided portable Nuclear Magnetic Resonance (NMR). It focuses on three main techniques: spin–lattice relaxation (recovery) time (T1), spin–spin relaxation (decay) time (T2), and Diffusion (D) techniques by testing whether or not the aforementioned techniques are in agreement with the gold standard and with each other when used for scanning breast tissue specimens with a variety of mammographic densities (MDs). The high mammographic density (HMD), intermediate MD, and low mammographic density (LMD) regions of each slice were identified according to the mammogram images. Subsequently, the grayscale values for these regions were quantified. One region was measured from the first sample while the remaining ones were measured from the second sample. The same areas were then exposed to portable NMR, and the sequences used as following: the stimulated echo sequence for diffusion (D), the Carr-Purcell-Meiboom-Gill (CPMG) sequence for T2, and saturation recovery sequence for T1. The correlations between the grayscale values and NMR techniques were strongly correlated. The Pearson correlation coefficient, R, of T1 (%) versus grayscale value, D (%) versus grayscale value, and T2 (%) versus grayscale value, was 0.91, 0.91, and 0.93, respectively. Furthermore, the relative water content of the breast slices based on T1, T2, and diffusion (D) measurements were strongly in agreement with each other. The Pearson correlation coefficient, R, of D (%) versus T1 (%), D (%) versus T2 (%), and T1 (%) versus T2 (%), was 0.984, 0.966, and 0.9868, respectively. The three pulse sequences can be employed in a portable NMR device to deliver continuous quantitative measurements of MD in breast tissue samples. As a result, the method demonstrated to be acceptable for determining the distribution of MDs among breast tissue samples without the need for additional qualitative analysis.</p