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The official journal of AMPI, IOMP and AFOMP
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2011| July-September | Volume 36 | Issue 3
Online since
August 4, 2011
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EDITORIAL
Unflattened photon beams from the standard flattening filter free accelerators for radiotherapy: Advantages, limitations and challenges
Sunil Dutt Sharma
July-September 2011, 36(3):123-125
DOI
:10.4103/0971-6203.83464
PMID
:21897556
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710
12
ORIGINAL ARTICLES
Development of image-processing software for automatic segmentation of brain tumors in MR images
C Vijayakumar, Damayanti Chandrashekhar Gharpure
July-September 2011, 36(3):147-158
DOI
:10.4103/0971-6203.83481
PMID
:21897560
Most of the commercially available software for brain tumor segmentation have limited functionality and frequently lack the careful validation that is required for clinical studies. We have developed an image-analysis software package called 'Prometheus,' which performs neural system-based segmentation operations on MR images using pre-trained information. The software also has the capability to improve its segmentation performance by using the training module of the neural system. The aim of this article is to present the design and modules of this software. The segmentation module of Prometheus can be used primarily for image analysis in MR images. Prometheus was validated against manual segmentation by a radiologist and its mean sensitivity and specificity was found to be 85.71±4.89% and 93.2±2.87%, respectively. Similarly, the mean segmentation accuracy and mean correspondence ratio was found to be 92.35±3.37% and 0.78±0.046, respectively.
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5
Variation of beam characteristics between three different wedges from a dual-energy accelerator
C Varatharaj, M Ravikumar, S Sathiyan, Sanjay S Supe
July-September 2011, 36(3):133-137
DOI
:10.4103/0971-6203.83475
PMID
:21897558
The use of megavoltage X-ray sources of radiation, with their skin-sparing qualities in radiation therapy, has been proved useful in relieving patient discomfort and allowing higher tumor doses to be given with fewer restrictions due to radiation effects in the skin. The purpose of this study was to compare the dosimetric characteristics of a physical and enhanced dynamic wedge from a dual-energy (6 and 18 MV) linear accelerator such as surfaces doses with different source to surface distances (SSD), half value layer (HVL) in water and peripheral doses for both available energies. At short SSD such as 85 cm, higher surface doses are produced by the lower wedges by the short wedge-to-skin distance. For physical wedged field, at heel edge side HVL value was high (17 cm) compared with the measured that of EDW (15.1 cm). It was noticed that, the HVL variation across the beam was significantly higher for 6 MV X-rays than for 18 MV X-rays. The lower wedge has the maximum variation of peripheral dose compared to other wedges. The three wedge systems discussed in this work possess vastly different dosimetric characteristics. These differences will have a direct impact on the choice of the wedge system to be used for a particular treatment. Complete knowledge of the dosimetric characterisitics, including the surface and peripheral doses, is crucial in proper choice of particular wedge systems in clinical use.
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1
Performance evaluation of three computed radiography systems using methods recommended in American Association of Physicists in Medicine Report 93
Wilbroad Muhogora, Renato Padovani, Faustino Bonutti, Peter Msaki, R Kazema
July-September 2011, 36(3):138-146
DOI
:10.4103/0971-6203.83478
PMID
:21897559
The performances of three clinical computed radiography (CR) systems, (Agfa CR 75 (with CRMD 4.0 image plates), Kodak CR 850 (with Kodak GP plates) and Kodak CR 850A (with Kodak GP plates)) were evaluated using six tests recommended in American Association of Physicists in Medicine Report 93. The results indicated variable performances with majority being within acceptable limits. The variations were mainly attributed to differences in detector formulations, plate readers' characteristics, and aging effects. The differences of the mean low contrast scores between the imaging systems for three observers were statistically significant for Agfa and Kodak CR 850A (
P
=0.009) and for Kodak CR systems (
P
=0.006) probably because of the differences in ages. However, the differences were not statistically significant between Agfa and Kodak CR 850 (
P
=0.284) suggesting similar perceived image quality. The study demonstrates the need to implement quality control program regularly.
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2
Comparison of no-prior and soft-prior regularization in biomedical microwave imaging
Amir H Golnabi, Paul M Meaney, Shireen D Geimer, Keith D Paulsen
July-September 2011, 36(3):159-170
DOI
:10.4103/0971-6203.83482
PMID
:21897561
Microwave imaging for medical applications is attractive because the range of dielectric properties of different soft tissues can be substantial. Breast cancer detection and monitoring of treatment response are areas where this technology could be important because of the contrast between normal and malignant tissue. Unfortunately, the technique is unable to achieve the high spatial resolution at depth in tissue which is available from other conventional modalities such as x-ray computed tomography (CT) or magnetic resonance imaging (MRI). We have incorporated a soft-prior regularization strategy within our microwave reconstruction algorithm and compared it with the images obtained with traditional no-prior (Levenberg-Marquardt) regularization. Initial simulation and phantom results show a significant improvement of the recovered electrical properties. Specifically, errors in the microwave property estimates were improved by as much as 95%. The effects of a false-inclusion region were also evaluated and the results show that a small residual property bias of 6% in permittivity and 15% in conductivity can occur that does not otherwise degrade the property recovery accuracy of inclusions that actually exist. The work sets the stage for integrating microwave imaging with MR for improved resolution and functional imaging of the breast in the future.
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11
TECHNICAL NOTES
Relative dosimetrical verification in high dose rate brachytherapy using two-dimensional detector array IMatriXX
A Manikandan, Sarkar Biplab, David A Perianayagam, R Holla, TR Vivek, N Sujatha
July-September 2011, 36(3):171-175
DOI
:10.4103/0971-6203.83491
PMID
:21897562
For high dose rate (HDR) brachytherapy, independent treatment verification is needed to ensure that the treatment is performed as per prescription. This study demonstrates dosimetric quality assurance of the HDR brachytherapy using a commercially available two-dimensional ion chamber array called IMatriXX, which has a detector separation of 0.7619 cm. The reference isodose length, step size, and source dwell positional accuracy were verified. A total of 24 dwell positions, which were verified for positional accuracy gave a total error (systematic and random) of −0.45 mm, with a standard deviation of 1.01 mm and maximum error of 1.8 mm. Using a step size of 5 mm, reference isodose length (the length of 100% isodose line) was verified for single and multiple catheters of same and different source loadings. An error ≤1 mm was measured in 57% of tests analyzed. Step size verification for 2, 3, 4, and 5 cm was performed and 70% of the step size errors were below 1 mm, with maximum of 1.2 mm. The step size ≤1 cm could not be verified by the IMatriXX as it could not resolve the peaks in dose profile.
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Dosimetric analysis of beam-matching procedure of two similar linear accelerators
Janhavi R Bhangle, VK Sathiya Narayanan, Namitha K Kumar, R Vaitheeswaran
July-September 2011, 36(3):176-180
DOI
:10.4103/0971-6203.83497
PMID
:21897563
Linear accelerators from the same vendor in a radiation therapy center are usually beam-matched following Vendor's acceptance criteria. This protocol is limited to check the difference at particular points on the ionization curve for depth dose or beam profiles. This article describes different tests done after commissioning to evaluate the level of agreement between matched beams of two ONCOR Impression plus linear accelerators from Siemens. Total scatter factors, collimator scatter factors, wedge transmission factors were measured in water for 6-MV photon. All these factors for ONCOR2 were within ±1% of those values for ONCOR1. Along with these point dose measurements we have essentially used γ-index to compare the planar dose distribution from two beam-matched accelerators. For this study a set of ready packed EDR2 films was exposed on both accelerators. The set consisted of films for percentage depth dose, beam profiles, a pyramid shape, multileaf collimator's positional and dose delivery accuracy, and a film to compare head scatter at tray level. To include treatment planning system calculations, a film kept in axial plane was exposed to 3DCRT and IMRT plans with actual gantry angles and monitor units. These films were analyzed for γ in OmniPro IMRT software using different combinations of ∆dose and - ∆distances. All these films have shown good agreement for - ∆distance of 3 mm and ∆dose of 3 %.
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ORIGINAL ARTICLES
A quality index for equivalent uniform dose
Francisco Cutanda Henríquez, Silvia Vargas Castrillón
July-September 2011, 36(3):126-132
DOI
:10.4103/0971-6203.83466
PMID
:21897557
Equivalent uniform dose (
EUD
) is the absorbed dose that, when homogeneously given to a tumor, yields the same mean surviving clonogen number as the given non-homogeneous irradiation.
EUD
is used as an evaluation tool under the assumption that two plans with the same value of
EUD
are equivalent, and their biological effect on the tumor (clonogen survival) would be the same as the one of a homogeneous irradiation of absorbed dose
EUD.
In this work, this assumption has been studied, and a figure of merit of its applicability has been obtained. Distributions of surviving clonogen number for homogeneous and non-homogeneous irradiations are found to be different even if their mean values are the same, the figure of merit being greater when there is a wider difference, and the equivalence assumption being less valid. Therefore,
EUD
can be closer to a uniform dose for some cases than for other ones (high α values, extreme heterogeneity), and the accuracy of the radiobiological indices obtained for evaluation, could be affected. Results show that the equivalence is very sensitive to the choice of radiobiological parameters, and this conclusion has been derived from mathematical properties of
EUD
.
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LETTER TO EDITOR
Need of patient-specific quality assurance and pre-treatment verification program for special plans in radiotherapy
Ramamoorthy Ravichandran, Saju Bhasi, JP Binukumar, CA Davis
July-September 2011, 36(3):181-183
DOI
:10.4103/0971-6203.83501
PMID
:21897564
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BOOK REVIEW
Review of Ph.D Thesis ''Dosimetric monitoring methods for megavoltage photon and electron beams in clinical radiotherapy''
R Ravichandran
July-September 2011, 36(3):184-185
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NEWS AND EVENTS
News and Events
T Ganesh
July-September 2011, 36(3):186-188
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th
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