Journal of Medical Physics
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   2016| January-March  | Volume 41 | Issue 1  
    Online since February 23, 2016

 
 
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ORIGINAL ARTICLES
Analysis of small field percent depth dose and profiles: Comparison of measurements with various detectors and effects of detector orientation with different jaw settings
Henry Finlay Godson, M Ravikumar, S Sathiyan, KM Ganesh, Y Retna Ponmalar, C Varatharaj
January-March 2016, 41(1):12-20
DOI:10.4103/0971-6203.177284  PMID:27051165
The advent of modern technologies in radiotherapy poses an increased challenge in the determination of dosimetric parameters of small fields that exhibit a high degree of uncertainty. Percent depth dose and beam profiles were acquired using different detectors in two different orientations. The parameters such as relative surface dose (DS), depth of dose maximum (Dmax), percentage dose at 10 cm (D10), penumbral width, flatness, and symmetry were evaluated with different detectors. The dosimetric data were acquired for fields defined by jaws alone, multileaf collimator (MLC) alone, and by MLC while the jaws were positioned at 0, 0.25, 0.5, and 1.0 cm away from MLC leaf-end using a Varian linear accelerator with 6 MV photon beam. The accuracy in the measurement of dosimetric parameters with various detectors for three different field definitions was evaluated. The relative DS(38.1%) with photon field diode in parallel orientation was higher than electron field diode (EFD) (27.9%) values for 1 cm ×1 cm field. An overestimation of 5.7% and 8.6% in D10depth were observed for 1 cm ×1 cm field with RK ion chamber in parallel and perpendicular orientation, respectively, for the fields defined by MLC while jaw positioned at the edge of the field when compared to EFD values in parallel orientation. For this field definition, the in-plane penumbral widths obtained with ion chamber in parallel and perpendicular orientation were 3.9 mm, 5.6 mm for 1 cm ×1 cm field, respectively. Among all detectors used in the study, the unshielded diodes were found to be an appropriate choice of detector for the measurement of beam parameters in small fields.
  3,172 295 -
REVIEW ARTICLE
Computed tomography imaging parameters for inhomogeneity correction in radiation treatment planning
Indra J Das, Chee-Wai Cheng, Minsong Cao, Peter A.S. Johnstone
January-March 2016, 41(1):3-11
DOI:10.4103/0971-6203.177277  PMID:27051164
Modern treatment planning systems provide accurate dosimetry in heterogeneous media (such as a patient’ body) with the help of tissue characterization based on computed tomography (CT) number. However, CT number depends on the type of scanner, tube voltage, field of view (FOV), reconstruction algorithm including artifact reduction and processing filters. The impact of these parameters on CT to electron density (ED) conversion had been subject of investigation for treatment planning in various clinical situations. This is usually performed with a tissue characterization phantom with various density plugs acquired with different tube voltages (kilovoltage peak), FOV reconstruction and different scanners to generate CT number to ED tables. This article provides an overview of inhomogeneity correction in the context of CT scanning and a new evaluation tool, difference volume dose-volume histogram (DVH), dV-DVH. It has been concluded that scanner and CT parameters are important for tissue characterizations, but changes in ED are minimal and only pronounced for higher density materials. For lungs, changes in CT number are minimal among scanners and CT parameters. Dosimetric differences for lung and prostate cases are usually insignificant (<2%) in three-dimensional conformal radiation therapy and < 5% for intensity-modulated radiation therapy (IMRT) with CT parameters. It could be concluded that CT number variability is dependent on acquisition parameters, but its dosimetric impact is pronounced only in high-density media and possibly in IMRT. In view of such small dosimetric changes in low-density medium, the acquisition of additional CT data for financially difficult clinics and countries may not be warranted.
  2,701 184 -
ORIGINAL ARTICLES
Investigation of grid performance using simple image quality tests
Dogan Bor, Ozlem Birgul, Umran Onal, Turan Olgar
January-March 2016, 41(1):21-28
DOI:10.4103/0971-6203.177280  PMID:27051166
Antiscatter grids improve the X-ray image contrast at a cost of patient radiation doses. The choice of appropriate grid or its removal requires a good knowledge of grid characteristics, especially for pediatric digital imaging. The aim of this work is to understand the relation between grid performance parameters and some numerical image quality metrics for digital radiological examinations. The grid parameters such as bucky factor (BF), selectivity (Σ), Contrast improvement factor (CIF), and signal-to-noise improvement factor (SIF) were determined following the measurements of primary, scatter, and total radiations with a digital fluoroscopic system for the thicknesses of 5, 10, 15, 20, and 25 cm polymethyl methacrylate blocks at the tube voltages of 70, 90, and 120 kVp. Image contrast for low- and high-contrast objects and high-contrast spatial resolution were measured with simple phantoms using the same scatter thicknesses and tube voltages. BF and SIF values were also calculated from the images obtained with and without grids. The correlation coefficients between BF values obtained using two approaches (grid parameters and image quality metrics) were in good agreement. Proposed approach provides a quick and practical way of estimating grid performance for different digital fluoroscopic examinations.
  2,219 120 -
TECHNICAL NOTES
Respiratory gated radiotherapy-pretreatment patient specific quality assurance
Rajesh Thiyagarajan, Sujit Nath Sinha, Ramamoorthy Ravichandran, Kothandaraman Samuvel, Girigesh Yadav, Ashok Kumar Sigamani, Vikraman Subramani, N Arunai Nambi Raj
January-March 2016, 41(1):65-70
DOI:10.4103/0971-6203.177279  PMID:27051173
Organ motions during inter-fraction and intra-fraction radiotherapy introduce errors in dose delivery, irradiating excess of normal tissue, and missing target volume. Lung and heart involuntary motions cause above inaccuracies and gated dose delivery try to overcome above effects. Present work attempts a novel method to verify dynamic dose delivery using a four-dimensional (4D) phantom. Three patients with mobile target are coached to maintain regular and reproducible breathing pattern. Appropriate intensity projection image set generated from 4D-computed tomography (4D-CT) is used for target delineation. Intensity modulated radiotherapy plans were generated on selected phase using CT simulator (Siemens AG, Germany) in conjunction with "Real-time position management" (Varian, USA) to acquire 4D-CT images. Verification plans were generated for both ion chamber and Gafchromic (EBT) film image sets. Gated verification plans were delivered on the phantom moving with patient respiratory pattern. We developed a MATLAB-based software to generate maximum intensity projection, minimum intensity projections, and average intensity projections, also a program to convert patient breathing pattern to phantom compatible format. Dynamic thorax quality assurance (QA) phantom (Computerized Imaging Reference Systems type) is used to perform the patient specific QA, which holds an ion chamber and film to measure delivered radiation intensity. Exposed EBT films are analyzed and compared with treatment planning system calculated dose. The ion chamber measured dose shows good agreement with planned dose within ± 0.5% (0.203 ± 0.57%). Gamma value evaluated from EBT film shows passing rates 92–99% (96.63 ± 3.84%) for 3% dose and 3 mm distance criteria. Respiratory gated treatment delivery accuracy is found to be within clinically acceptable level.
  2,137 164 -
ORIGINAL ARTICLES
Application of Chang's attenuation correction technique for single-photon emission computed tomography partial angle acquisition of Jaszczak phantom
Krishnendu Saha, Sean C Hoyt, Bryon M Murray
January-March 2016, 41(1):29-33
DOI:10.4103/0971-6203.177278  PMID:27051167
The acquisition and processing of the Jaszczak phantom is a recommended test by the American College of Radiology for evaluation of gamma camera system performance. To produce the reconstructed phantom image for quality evaluation, attenuation correction is applied. The attenuation of counts originating from the center of the phantom is greater than that originating from the periphery of the phantom causing an artifactual appearance of inhomogeneity in the reconstructed image and complicating phantom evaluation. Chang's mathematical formulation is a common method of attenuation correction applied on most gamma cameras that do not require an external transmission source such as computed tomography, radionuclide sources installed within the gantry of the camera or a flood source. Tomographic acquisition can be obtained in two different acquisition modes for dual-detector gamma camera; one where the two detectors are at 180° configuration and acquire projection images for a full 360°, and the other where the two detectors are positioned at a 90° configuration and acquire projections for only 180°. Though Chang's attenuation correction method has been used for 360° angle acquisition, its applicability for 180° angle acquisition remains a question with one vendor's camera software producing artifacts in the images. This work investigates whether Chang's attenuation correction technique can be applied to both acquisition modes by the development of a Chang's formulation-based algorithm that is applicable to both modes. Assessment of attenuation correction performance by phantom uniformity analysis illustrates improved uniformity with the proposed algorithm (22.6%) compared to the camera software (57.6%).
  1,747 87 -
The modulating effect of royal jelly consumption against radiation-induced apoptosis in human peripheral blood leukocytes
Navid Rafat, Ali Shabestani Monfared, Maryam Shahidi, Tayyeb Allahverdi Pourfallah
January-March 2016, 41(1):52-57
DOI:10.4103/0971-6203.177281  PMID:27051171
The present work was designed to assess the radioprotective effect of royal jelly (RJ) against radiation-induced apoptosis in human peripheral blood leukocytes. In this study, peripheral blood samples were obtained on days 0, 4, 7, and 14 of the study from six healthy male volunteers taking a 1000 mg RJ capsule orally per day for 14 consecutive days. On each sampling day, all collected whole blood samples were divided into control and irradiated groups which were then exposed to the selected dose of 4 Gy X-ray. Percentage of apoptotic cells (Ap %) was evaluated for all samples immediately after irradiation (Ap0) and also after a 24 h postirradiation incubation at 37°C in 5% CO2 (Ap24) by the use of neutral comet assay. Concerning Ap0, collected data demonstrated that the percentage of apoptotic cells in both control and irradiated groups did not significantly change during the study period. However, with respect to Ap24, the percentage of apoptotic cells in irradiated groups gradually reduced during the experiment, according to which a significant decrease was found after 14 days RJ consumption (P = 0.002). In conclusion, the present study revealed the protective role of 14 days RJ consumption against radiation-induced apoptosis in human peripheral blood leukocytes.
  1,552 117 -
Evaluation of various boluses in dose distribution for electron therapy of the chest wall with an inward defect
Hoda Mahdavi, Keyvan Jabbari, Mahnaz Roayaei
January-March 2016, 41(1):38-44
DOI:10.4103/0971-6203.177288  PMID:27051169
Delivering radiotherapy to the postmastectomy chest wall can be achieved using matched electron fields. Surgical defects of the chest wall change the dose distribution of electrons. In this study, the improvement of dose homogeneity using simple, nonconformal techniques of thermoplastic bolus application on a defect is evaluated. The proposed phantom design improves the capability of film dosimetry for obtaining dose profiles of a patient's anatomical condition. A modeled electron field of a patient with a postmastectomy inward surgical defect was planned. High energy electrons were delivered to the phantom in various settings, including no bolus, a bolus that filled the inward defect (PB0), a uniform thickness bolus of 5 mm (PB1), and two 5 mm boluses (PB2). A reduction of mean doses at the base of the defect was observed by any bolus application. PB0 increased the dose at central parts of the defect, reduced hot areas at the base of steep edges, and reduced dose to the lung and heart. Thermoplastic boluses that compensate a defect (PB0) increased the homogeneity of dose in a fixed depth from the surface; adversely, PB2 increased the dose heterogeneity. This study shows that it is practical to investigate dose homogeneity profiles inside a target volume for various techniques of electron therapy.
  1,437 189 -
Analyzing the characteristics of 6 MV photon beam at low monitor unit settings
L Nithya, N Arunai Nambi Raj, Sasikumar Rathinamuthu
January-March 2016, 41(1):34-37
DOI:10.4103/0971-6203.177285  PMID:27051168
Analyzing the characteristics of a low monitor unit (MU) setting is essential, particularly for intensity-modulated techniques. Intensity modulation can be achieved through intensity-modulated radiotherapy (IMRT) or volumetric-modulated arc therapy (VMAT). There is possibility for low MUs in the segments of IMRT and VMAT plans. The minimum MU/segment must be set by the physicist in the treatment planning system at the time of commissioning. In this study, the characteristics such as dose linearity, stability, flatness, and symmetry of 6 MV photon beam of a Synergy linear accelerator at low MU settings were investigated for different dose rates. The measurements were performed for Synergy linear accelerator using a slab phantom with a FC65-G chamber and Profiler 2. The MU linearity was studied for 1–100 MU using a field size of 10 cm ×10 cm. The linearity error for 1 MU was 4.2%. Flatness of the beam was deteriorated in 1 MU condition. The beam stability and symmetry was well within the specification. Using this study, we conclude that the treatment delivered with <3 MU may result in uncertainty in dose delivery. To ensure the correct dose delivery with less uncertainty, it is recommended to use ≥3 MU as the minimum MU per segment in IMRT and VMAT plans.
  1,380 174 -
Comparison of computed tomography dose index in polymethyl methacrylate and nylon dosimetry phantoms
Supawitoo Sookpeng, Patsuree Cheebsumon, Thanyawee Pengpan, Colin Martin
January-March 2016, 41(1):45-51
DOI:10.4103/0971-6203.177287  PMID:27051170
The use of computed tomography (CT) scanning has been growing steadily. Therefore, CT dose measurement is becoming increasingly important for patient protection and optimization. A phantom is an important tool for dose measurement. This paper focuses on the evaluation of a CT dosimetry phantom made from nylon, instead of the standard polymethyl methacrylate (PMMA), which is not readily available or is too expensive in some countries. Comparison between phantoms made from the two materials is made in terms of measurements of the CT dose indices (CTDI). These were measured for four different beam widths and kVp settings at the center and periphery in head and body phantoms made from both materials and weighted CTDIs (CTDIw) were calculated. CT numbers along the z-axis of the phantom were also measured at the center and four peripheral positions of each scanned slice to check phantom homogeneity. Results showed that values for the CTDIw measured in the nylon phantoms were slightly higher than those from the PMMA while CT numbers for nylon were lower than those of PMMA. This is because the mass attenuation coefficient of the nylon is higher. Nylon could be used as a substitute material for CT dosimetry phantom to enable measurements and adjustment factors are given which could be used to estimate PMMA values for making comparisons with displayed values.
  1,451 85 -
TECHNICAL NOTES
Comparison of two programs in calculating electron output factors at extended source-surface distances
Yunfei Hu, Jonathan Andrew Lambert, Yang Wang
January-March 2016, 41(1):58-64
DOI:10.4103/0971-6203.177283  PMID:27051172
Monitor units (MUs) calculated by radiotherapy treatment planning systems need to be verified independently. At extended source-surface distances (SSDs), different output factors (OFs) can be given by different independent MU checking packages due to the calculation methods used and assumptions made within them. The accuracy of two software packages - RadCalc® (LifeLine Software Inc., Austin, USA) and eDatabook (Y. Wang, Radiation Oncology Institute, Sydney, AUS) - was determined by comparing the calculated OFs directly to measured OFs for a series of standard electron cutouts on an Elekta Synergy linear accelerator at standard and extended SSDs (100 cm and above). For the majority of the measurements made, eDatabook provided OFs closer to the measured value than RadCalc; however, in two cases, eDatabook was unable to provide a factor. RadCalc failed to calculate the OFs accurately at extended SSDs as its calculation is based on the assumption that the established effective-SSD curve can accurately predict the data where there are no measurements available. The accuracy of eDatabook is due to its use of a linear interpolation to determine the OF at an extended SSD when there are no measurement data available.
  1,284 127 -
EDITORIAL
Ten years of online publication of Journal of Medical Physics
Ambika Sahai Pradhan
January-March 2016, 41(1):1-2
DOI:10.4103/0971-6203.177276  PMID:27051163
  1,155 156 -
LETTERS TO EDITOR
In regard to “Setup error analysis in helical tomotherapy based image-guided radiation therapy treatments”
Slav Yartsev
January-March 2016, 41(1):71-71
DOI:10.4103/0971-6203.177275  PMID:27051174
  868 98 -
Reply to the comments on “Setup error analysis in helical tomotherapy based image-guided radiation therapy treatments” by Slav Yartsev
Bhagyalakshmi Akkavil Thondykandy, Jamema V Swamidas, Jay Prakash Agarwal, Tejpal Gupta, Sarbani G Laskar, Umesh Mahantshetty, Shrinivasan S Iyer, Indrani U Mukherjee, Shyam K Shrivastava, Deepak D Deshpande
January-March 2016, 41(1):72-72
DOI:10.4103/0971-6203.177282  PMID:27051175
  829 97 -
BOOK REVIEW
Basic radiotherapy physics and biology
Hamid Abdollahi
January-March 2016, 41(1):77-79
  790 135 -
NEWS
”Observations in medical physics” - Excerpts from oration of Prof. I J Das on Ramaiah Naidu Memorial Oration Award* 2015

January-March 2016, 41(1):73-76
  505 97 -
ACKNOWLEDGMENT
Acknowledgment

January-March 2016, 41(1):80-80
  433 112 -
 
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