Journal of Medical Physics
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   Table of Contents - Current issue
July-September 2020
Volume 45 | Issue 3
Page Nos. 143-196

Online since Tuesday, October 13, 2020

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Dose calculation comparisons between three modern treatment planning systems p. 143
Courtney Bosse, Ganesh Narayanasamy, Daniel Saenz, Pamela Myers, Neil Kirby, Karl Rasmussen, Panayiotis Mavroidis, Niko Papanikolaou, Sotirios Stathakis
Purpose: Monaco treatment planning system (TPS) version 5.1 uses a Monte-Carlo (MC)-based dose calculation engine. The aim of this study is to verify and compare the Monaco-based dose calculations with both Pinnacle3 collapsed cone convolution superposition (CCCS) and Eclipse anisotropic analytical algorithm (AAA) calculations. Materials and Methods: For this study, 18 previously treated lung and head-and-neck (HN) cancer patients were chosen to compare the dose calculations between Pinnacle, Monaco, and Eclipse. Plans were chosen from those that had been treated using the Elekta VersaHD or a Novalis Tx linac. All of the treated volumetric-modulated arc therapy plans used 6 MV or 10 MV photon beams. The original plans calculated with CCCS or AAA along with the recalculated ones using MC from the three TPS were exported into Velocity software for intercomparison. Results: To compare the dose calculations, Planning target volume (PTV) heterogeneity indexes and conformity indexes were calculated from the dose volume histograms (DVH) of all plans. While mean lung dose (MLD), lung V5 and V20 values were recorded for lung plans, the computed dose to parotids, brainstem, and mandible were documented for HN plans. In plan evaluation, percent differences of the above dosimetric values in Monaco computation were compared against each of the other TPS computations. Conclusion: It could be concluded through this research that there can be differences in the calculation of dose across different TPSs. Although relatively small, these differences could become apparent when compared using DVH. These differences most likely arise from the different dose calculation algorithms used in each TPS. Monaco employs the MC allowing it to have much more detailed calculations that result in it being seen as the most accurate and the gold standard.
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Dosimetric comparison of different planning techniques in left-sided whole-breast irradiation: A planning study p. 148
L Nithya, Vineeta Goel, Deepti Sharma, Karthik Vittal, Nidhi Marjara
Purpose: This planning study compared the various dosimetric parameters of different types of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) techniques for left-sided breast cancer radiotherapy. Materials and Methods: Treatment of 22 left-sided breast cases was planned using two IMRT and VMAT techniques for the prescription of 40 Gy in 15 fractions. For tangential IMRT (Tan_IMRT), five beams were placed as conventional tangential beams. For equally spaced IMRT (Equi_IMRT), six beams were placed equidistantly at 40° interval from 300° to 140°. For tangential VMAT (Tan_VMAT), two arcs were used with the avoidance sector in such a way that the beam covered like tangential fields. For full-arc VMAT (Full_VMAT), similar arcs as Tan_VMAT were used, without avoidance sector. All treatment plans were generated using Eclipse planning system for TrueBeam STx linear accelerator. For planning target volume (PTV), dose parameters including D95%,D99%,V105%,homogeneity index (HI), and conformity index (CI) were analyzed. Different dose parameters for the left lung, heart, left anterior descending artery (LAD), right lung, and right breast were also analyzed. In addition, low-dose spillage in the normal tissues and the number of monitor units (MUs) required for the treatment were compared. Results: IMRT technique exhibited superior D95%and D99%for PTV compared with VMAT techniques. VMAT plans provided more V105%(6%) compared with that of IMRT plans (approximately 1%). HI was better in IMRT plans (Tan_IMRT, 0.085 ± 0.015; Equi_IMRT, 0.094 ± 0.011) than in VMAT plans. CI was better in VMAT plans. The mean lung dose (7.7 Gy ± 1.788 Gy) and V5Gy(34.99% ± 6.799%) were better achieved in Tan_IMRT plan than other plans. Right lung, heart, and right breast sparing were better achieved in Tan_IMRT plan. Moreover, low-dose spillage was very less in the Tan_IMRT compared with all other techniques. Conclusion: Dosimetric comparison in this study showed that tangential IMRT technique is superior in terms of target coverage, sparing of lung, heart, and right breast, and low-dose spillage control in the left-sided breast-only radiotherapy.
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Objective assessment of the quality and accuracy of deformable image registration p. 156
Ines-Ana Jurkovic, Nikos Papanikolaou, Sotirios Stathakis, Neil Kirby, Panayiotis Mavroidis
Background: The increased use of deformable registration algorithms in clinical practice has also increased the need for their validation. Aims and Objectives: The purpose of the study was to investigate the quality, accuracy, and plausibility of three commercial image registration algorithms for 4-dimensional computed tomography (4DCT) datasets using various similarity measures. Materials and Methods: 4DCT datasets were acquired for 10 lung cancer patients. 23 similarity measures were used to evaluate image registration quality. To ensure selected method's invertibility and assess resultant mechanical stress, the determinant of the Jacobian for the displacement field and 3-D Eulerian strain tensor were calculated. All the measures and calculations were applied on to extended deformable multi pass (EXDMP) and deformable multi pass (DMP) methods. Results: The results indicate the same trend for several of the studied measures. The Jacobian determinant values were always positive for the DMP method. The Eulerian strain tensor had smaller values for the DMP method than EXDMP in all of the studied cases. The negative values of the Jacobian determinant point to non-physical behavior of the EXDMP method. The Eulerian strain tensor values indicate less tissue strain for the DMP method. Large differences were also observed in the results between complete and cropped datasets (coefficient of determination: 0.55 vs. 0.93). Conclusion: A number of error and distance measures showed the best performance among the tested measures. The evaluated measures might detect CT dataset differences with higher precision if the analysis is restricted to a smaller volume.
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Gradient based elastic property reconstruction in digital image correlation elastography p. 168
Alexandre Brazy, Elijah Van Houten
Aim: A Conjugate Gradient implementation of the Digital Image Correlation Elastography method is presented. Method: The gradient is calculated using the adjoint method, requiring only two forward solutions regardless of the number of mechanical properties to reconstruct. A power-law based multi-frequency viscoelastic model is used to relate the reconstructed mechanical properties and the Digital Image Correlation surface displacement measurements. Result: The method is tested against harmonic surface motion fields generated through numerical simulation and measured on a silicon phantom. Conclusion: Reconstruction results show the ability of the gradient reconstruction method to detect stiff internal inclusions in simulated and phantom data.
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Influence of air gap under bolus in the dosimetry of a clinical 6 MV photon beam p. 175
Dilson Lobo, Sourjya Banerjee, Challapalli Srinivas, Ramamoorthy Ravichandran, Suman Kumar Putha, PU Prakash Saxena, Shreyas Reddy, Johan Sunny
Aim: In some situations of radiotherapy treatments requiring application of tissue-equivalent bolus material (e.g., gel bolus), due to material's rigid/semi-rigid nature, undesirable air gaps may occur beneath it because of irregularity of body surface. The purpose of this study was to evaluate the dosimetric parameters such as surface dose (Ds), depth of dose maximum (dmax), and depth dose along central axis derived from the percentage depth dose (PDD) curve of a 6 MV clinical photon beam in the presence of air gaps between the gel bolus and the treatment surface. Materials and Methods: A bolus holder was designed to hold the gel bolus sheet to create an air gap between the bolus and the radiation field analyzer's (RFA-300) water surface. PDD curves were taken for field sizes of 5 cm × 5 cm, 10 cm × 10 cm, 15 cm × 15 cm, 20 cm × 20 cm, and 25 cm × 25 cm, with different thicknesses of gel bolus (0.5, 1.0, and 1.5 cm) and air gap (from 0.0 to 3.0 cm), using a compact ionization chamber (CC13) with RFA-300 keeping 100 cm source-to-surface (water) distance. The dosimetric parameters, for example, "Ds," "dmax," and difference of PDD (maximum air gap vs. nil air gap), were analyzed from the obtained PDD curves. Results: Compared to ideal conditions of full contact of bolus with water surface, it has been found that there is a reduction in "Ds" ranging from 14.8% to 3.2%, 14.9% to 1.1%, and 12.6% to 0.7% with the increase of field size for 0.5, 1.0, and 1.5 cm thickness of gel boluses, respectively, for maximum air gap. The "dmax" shows a trend of moving away from the treatment surface, and the maximum shift was observed for smaller field size with thicker bolus and greater air gap. The effect of air gap on PDD is minimal (≤1%) beyond 0.4 cm depth for all bolus thicknesses and field sizes except for 5 cm × 5 cm with 1.5 cm bolus thickness. Conclusions: The measured data can be used to predict the probable effect on therapeutic outcome due to the presence of inevitable air gaps between the bolus and the treatment surface.
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Assessment of regional pediatric diagnostic reference levels for panoramic radiography using dose area product p. 182
Amal Jose, A Saravana Kumar, KN Govindarajan, P Manimaran
Aim: The current work aims to calculate dose area product (DAP) and to determine regional diagnostic reference level (DRL) for pediatric panoramic radiography in Tamil Nadu. Materials and Methods: In this study, DAP was calculated after finding the product of air kerma on the detector side of scanner with the corresponding exposed area. The obtained DAP values were further analyzed, and DRL was calculated using Microsoft Excel. The study was carried out with routine pediatric exposure parameters. Results: The obtained mean, range, and third quartile values for pediatric panoramic radiography are found to be 65 mGycm2, 11–148 mGycm2, and 82 mGycm2, respectively. The proposed DRL is comparable with the other countries' DRL. Conclusion: Based on the results of the present study, it was observed that there exists a wide difference in mean doses among the panoramic scanners. The variation in radiation doses between the clinics/hospitals and similar scanners suggests a large potential for optimization of panoramic procedures.
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Effect of smartphone light fluxes on cornea: A biophysical study Highly accessed article p. 187
PM Dongre, Vinod D Jaiswal, Suraj Singh
Objective: Biophysical study to investigate (a) the effects of smartphone light fluxes (SPLF) on isolated mammalian cornea and model protein (insulin), (b) to predict the possible visual interference of SPLF. Materials and Methods: Fresh goat cornea and insulin protein were used as an experimental model system. The energy of absorbed SPLF was measured using chemical dosimeter. The effect of SPLF on the aggregation of model protein was studied using fluorescence spectroscopy and dynamic light scattering (DLS). Fluorescence microscopy, scanning electron microscopy (SEM), DLS, were used for cornea imaging. Results: The spectral emission peak of SPLF was observed at 380 nm and 420 nm. Absorbed radiation of SPLF was found to be 2.82 mWm-2 and 1.92 mWm-2 for collimated (focussed) and noncollimated (nonfocussed) condition, respectively. Secondary structural changes of insulin were observed by fluorescence and zeta potential after SPLF exposure. SEM study revealed the disorganization of the epithelial cell surface, increase in intercellular space, disorganization of primary epithelium layer, and exposure of the second layer is seen in depth. Differential Interference Microscopy showed an optical gradient in images that appears to be changed in specimen structure. Fluorescence microscopy showed disorganization in epithelial cell pattern. A significant difference in bio-molecular permeation was observed in the exposed cornea. Ultraviolet UV-visible spectroscopy study indicated a reduction in light transmission through the cornea. Conclusions: The obtained results indicate changes in physicochemical and morphological modifications in the cornea and insulin modifications after exposed to SPLF.
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Proton therapy physics (Second Edition) p. 195
Dayananda Shamurailatpam Sharma
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