Maintaining a sharp lateral dose falloff in pencil beam scanning (PBS) proton therapy is crucial for sparing organs at risk (OARs), especially when they are in close proximity to the target volume. The most common approach to improve lateral dose falloff is through the use of physical beam shaping devices, such as brass apertures or collimator based systems. A recently proposed approach focuses on proton beam spot placements, moving away from traditional grid-based placements to concentric-contours based schemes. This improves lateral dose falloff in two ways: (1) by better conforming all spots to the tumor boundary and (2) allowing for ‘edge enhancement’, where boundary spots deliver higher fluence than more central spots, thereby creating a steeper lateral dose falloff. However, these benefits come at the expense of maintaining uniformity of spot distribution inside the target volume. In this work we have developed a new optimized spot placement scheme that provides robust spot distributions inside the target. This approach achieves the boundary conformity of a concentric-contours based approach and uses a fast-iterative method to distribute the interior spots in a highly uniform fashion in an attempt to improve both the lateral dose falloff and uniformity. Furthermore, we quantified the impact of this new approach through direct comparison with grid, contour, and hybrid spot placements schemes, showing improvements for this new approach. The results were validated in homogeneous medium for two different target shapes having concave and convex geometry.
Objective: To determine the frequency and causes of pericardial effusion in patients presenting to emergency department with dyspnea. Study Design: Prospective/Observational study Place & Duration:Cardiac Centre, Pakistan Institute of Medical Sciences (PIMS),Islamabad for duration of one year from January 2019 to Dec 2019. Methods: A total 220 patients of both genders with ages above 20 years presented with dyspnea were enrolled in this study. Patients detailed medical history was recorded after taking informed consent. All patients had received echocardiography to examine the incidence of pericardial effusion. Causes of pericardial effusion were recorded. Data was analyzed by SPSS 24.0. Results: Out of 220 patients 38 (17.27%) patients had pericardial effusion. Among these 26 (68.42%) were males while rest 31.58% patients were females. 5 (13.16%) patients had ages <40 years while 33 (86.84%) patients had ages >40 years. 20 (52.63%) patients had small size effusion, 15 (39.47%) patients had moderate size and 3 (7.89%) patients had large size effusion. Neoplastic diseases were the commonest cause of pericardial effusion found in 15 (39.47%) patients followed by idiopathic in 10 (26.32%), uremia in 6 (15.79%) patients, 3 (7.89%) patients had bacterial infections, 3 (7.89%) had HIV positive and 1 (2.63%) patient had other. Conclusion: It is concluded that incidence of pericardial effusion is high in patients with unexplained dyspnea. Neoplastic was the commonest cause of pericardial effusion. Keywords: Pericardial Effusion, Frequency, Causes, Dyspnea. Electrocardiogram
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