Quality assurance and quality control
Damian Tolan, Rachel Hyland, Christopher Taylor, Arnold Cowen in Get Through, 2020
False – an electronic penetrameter is normally used to measure the penetration of x-rays when placed in the primary beam from an x-ray tube and estimates the kVp from this. A potential divider is an invasive kV measurement device that is not normally used for quality assurance (QA) checks.True – after a series of exposures a film test strip can be analysed with a densitometer and a characteristic film curve can be plotted. This can then be used to calculate film gamma.True – for conventional x-ray work, this is regarded as an acceptable tolerance. In mammography, the tube voltage is expected to be correct to within ± 1 kV.True – each edge of the x-ray field should be within 1 cm of the edge of the light field for a 20 × 20 field at 1 m. This means an error of up to 10% is possible.True – 25–50% variation is allowed from the manufacturer’s specification.
Quantifying Differences in Dose Distributions
Ben Mijnheer in Clinical 3D Dosimetry in Modern Radiation Therapy, 2017
Since its introduction, gamma has become one of the more commonly used tools to quantitatively assess differences in dose distributions. This is especially true when comparing measured versus calculated dose distributions, as is commonly done for IMRT QA. Figure 14.4 shows an example gamma calculation for a TomoTherapy plan delivered to a cylindrical solid water phantom containing a sheet of radiographic film. In this case, the reference dose was taken to be the dose measured by the film, whereas the evaluated distribution is the dose distribution resulting from calculation of the treatment plan on the phantom geometry. Values for and are 3% of the maximum reference dose and 3 mm, respectively. The color map indicates regions with different values of gamma. Regions that are not colored fall below the lowest color band .
Dictionary
Mario P. Iturralde in Dictionary and Handbook of Nuclear Medicine and Clinical Imaging, 1990
Gamma camera. An imaging apparatus used to visualize the distribution of radionuclides within the body. The majority of gamma cameras in clinical use operate on the principle devised originally by H. O. Anger at the Donner Laboratory in Berkeley in 1956. Radiation emanating from the patient is detected by a single, large, circular NaI(Tl) scintillation crystal. An array of (37, 61, or 91) photomultiplier tubes detects the light quanta emitted by the crystal and converts their energies into electrical pulses. Associated electronic circuitry determines the x, y coordinates of each scintillation event, the outputs of all the tubes being summed to provide a z pulse, the amplitude of which corresponds to the total energy of the scintillation event. The distribution of radioactivity is usually displayed on an oscilloscope. For quantitative analysis, the gamma camera is connected to a dedicated microcomputer, radioactive distributions being displayed either on a monochrome TV monitor as a gray scale range of tones or on a color TV monitor as a color scale.
Comparing the DNA-damage RBE of intraoperative and conventional electron beams using a hybrid simulation approach
Published in International Journal of Radiation Biology, 2023
Hamid Reza Baghani, Ali Shiri, Hamid Gholamhosseinian
Gamma analysis was performed using a validated hand-written program that is released by GitHub and is developed by MATLAB programming software (Geurts 2018). The dose difference (DD) and distance to agreement (DTA) values were respectively set to 2% and 2 mm during the gamma index calculations. Gamma values lower than unity are scored as an accordance between the measurement and Monte Carlo results, while greater gamma index values mean the failure of comparison. The fidelity of the introduced Monte Carlo models of LIAC and Varian Linacs was also evaluated by the R-squared statistical test. In this regard, the simulation results were plotted against the measurement data and the correlation between the results was evaluated through fitting a linear curve (with the fixed slope of unity) to the drawn scatter data. Then, the adjusted R-square value (R2) of the fitted linear curve was reported for all considered PDD and TDP validation data.
Modeling dragonfly population data with a Bayesian bivariate geometric mixed-effects model
Published in Journal of Applied Statistics, 2023
Yulan B. van Oppen, Gabi Milder-Mulderij, Christophe Brochard, Rink Wiggers, Saskia de Vries, Wim P. Krijnen, Marco A. Grzegorczyk
For the random effect covariance matrix 12), we follow [3] and impose a Multivariate Generalized Hyperbolic t prior distribution on its inverse: d = 2 is the dimension of 17], the MGH-t distribution is less informative than an inverse-Wishart distribution in a marginal sense. The v + d−1 degrees of freedom, where rate parameter of the Gamma distribution. For the density of the joint posterior distribution of the model parameters, we obtain j (7) but parameterized through its continuitized medians from (9). The relationship between 11). A graphical representation of the model is given in Figure 1. To generate parameter samples from the posterior distribution, we use a Metropolis-Hastings Markov Chain Monte Carlo (MCMC) sampling scheme. We refer to Section 3 for more technical details.
Interaction between astrocytes and neurons in simulated space radiation-induced CNS injury
Published in International Journal of Radiation Biology, 2023
Mengjin Liu, Yu Lan, Yuhan Qin, Yanan Gao, Yulin Deng, Nuomin Li, Chen Zhang, Hong Ma
Gamma radiation is often used as a model of ionizing radiation in space (Fu et al. 2020). Here, we treated astrocytes (U87 MG) and neuronal cells (SH-SY5Y) with different doses of γ-ray, and cell survival rate were measured. The result showed that 0.5 Gy and 1 Gy γ-ray treatment did not significant influenced the cell survival rate (Figure S1). However, the survival rate of both U87 MG and SH-SY5Y cells was significantly decreased after 2 Gy γ-ray treatment (approximately 75% of the control group). So, we chose 2 Gy γ-ray for further study. Next, we detected the levels of oxidative stress and inflammation markers. We found that the levels of H2O2 were increased in U87 MG and SH-SY5Y cells after γ-ray treatment (Figure 1(B)). Moreover, the results of real-time PCR analysis showed that the expression levels of IL-6 and TNF-α were significantly upregulated in U87 MG and SH-SY5Y cells treated with γ-ray (Figure 1(C,D)). To further confirm that γ-ray radiation caused oxidative and inflammatory damage in CNS cells. We incubated γ-ray treated cells with Dragon’s Blood extract (DBE), a traditional Chinese medicine that alleviated the nerve damage induced by irradiation in rat via its anti-inflammatory and antioxidant effects in our previous study (Xin et al. 2012). The results showed that DBE restored cell survival rate and inhibited the increase of H2O2 levels and upregulation of TNF-α and IL-6 induced by γ-ray radiation in U87 MG and SH-SY5Y cells (Figure S2). Together, these results demonstrated that γ-ray induce oxidative and inflammatory damage in U87 MG and SH-SY5Y cells.
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