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2010| October-December | Volume 35 | Issue 4
Online since
October 19, 2010
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ORIGINAL ARTICLES
Experimental determination of the weighting factor for the energy window subtraction-based downscatter correction for I-123 in brain SPECT studies
Robin de Nijs, Søren Holm, Gerda Thomsen, Morten Ziebell, Claus Svarer
October-December 2010, 35(4):215-222
DOI
:10.4103/0971-6203.71765
PMID
:21170186
Correction for downscatter in I-123 SPECT can be performed by the subtraction of a secondary energy window from the main window, as in the triple-energy window method. This is potentially noise sensitive. For studies with limited amount of counts (e.g. dynamic studies), a broad subtraction window with identical width is preferred. This secondary window needs to be weighted with a factor higher than one, due to a broad backscatter peak from high-energy photons appearing at 172 keV. Spatial dependency and the numerical value of this weighting factor and the image contrast improvement of this correction were investigated in this study. Energy windows with a width of 32 keV were centered at 159 keV and 200 keV. The weighting factor was measured both with an I-123 point source and in a dopamine transporter brain SPECT study in 10 human subjects (5 healthy subjects and 5 patients) by minimizing the background outside the head. Weighting factors ranged from 1.11 to 1.13 for the point source and from 1.16 to 1.18 for human subjects. Point source measurements revealed no position dependence. After correction, the measured specific binding ratio (image contrast) increased significantly for healthy subjects, typically by more than 20%, while the background counts outside of all subjects were effectively removed. A weighting factor of 1.1-1.2 can be applied in clinical practice. This correction effectively removes downscatter and significantly improves image contrast inside the brain.
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TECHNICAL NOTES
Indoor radon survey in a university campus of Nigeria
RI Obed, HT Lateef, AK Ademola
October-December 2010, 35(4):242-246
DOI
:10.4103/0971-6203.71760
PMID
:21170190
CR-39 tracketch detectors were used for the measurement of
222
Rn concentration in 24 offices in Nigeria's oldest university campus in order to estimate the effective dose to the occupants from
222
Rn and its progeny. The dosimetric measurements were made over a period of 3 months. Questionnaires were distributed and analyzed. The radon concentration ranged from 157 to 495 Bq /m
3
, with an arithmetic mean and standard deviation of 293.3 and 79.6 Bq/ m
3
, respectively. The effective dose to the workers was estimated and this varied from 0.99 to 3.12 mSv/ y, with a mean of 1.85 mSv /y. The radon concentrations were found to be within the reference levels of ICRP.
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ORIGINAL ARTICLES
Automatic and manual image fusion of
111
In-pentetreotide SPECT and diagnostic CT in neuroendocrine tumor imaging - An evaluation
Elisabeth Hedlund, Jan-Erik Karlsson, Sven-Åke Starck
October-December 2010, 35(4):223-228
DOI
:10.4103/0971-6203.71766
PMID
:21170187
In the clinical diagnosis of neuroendocrine tumors (NET), the results of examinations, such as high-resolution computed tomography (CT) and single photon computerized tomography (SPECT), have conventionally been interpreted separately. The aim of the present study was to evaluate Hermes Multimodality™ 5.0 H Image Fusion software-based automatic and manual image fusion of SPECT and CT for the localization of NET lesions. Out of 34 NET patients who were examined by means of somatostatin receptor scintigraphy (SRS) with 111In- pentetreotide along with SPECT, 22 patients had a CT examination of the abdomen, which was used in the fusion analysis. SPECT and CT data were fused using software with a registration algorithm based on normalized mutual information. The criteria for acceptable fusion were established at a maximum cranial or caudal dislocation of 25 mm between the images and at a reasonable consensus (in order of less than 1 cm) between outline of the reference organs. The automatic fusion was acceptable in 13 of the 22 examinations, whereas 9 fusions were not. However all the 22 examinations were acceptable at the manual fusion. The result of automatic fusion was better when the slice thickness of 5 mm was applied at CT examination, when the number of slices was below 100 in CT data and when both examinations included uptakes of pathological lesions. Retrospective manual image fusion of SPECT and CT is a relatively inexpensive but reliable method to be used in NET imaging. Automatic image fusion with specified software of SPECT and CT acts better when the number of CT slices is reduced to the SPECT volume and when corresponding pathological lesions appear at both SPECT and CT examinations.
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134
Electron beam characteristics at extended source-to-surface distances for irregular cut-outs
T Arunkumar, Sanjay S Supe, M Ravikumar, S Sathiyan, M Ganesh
October-December 2010, 35(4):207-214
DOI
:10.4103/0971-6203.71763
PMID
:21170185
Electron beam therapy is widely used in the management of cancers. The rapid dose fall-off and the short range of an electron beam enable the treatment of lesions close to the surface, while sparing the underlying tissues. In an extended source-to-surface (SSD) treatment with irregular field sizes defined by cerrobend cutouts, underdosage of the lateral tissue may occur due to reduced beam flatness and uniformity. To study the changes in the beam characteristics, the depth dose, beam profile, and isodose distributions were measured at different SSDs for regular 10 Χ 10 cm
2
and 15 Χ 15 cm
2
cone, and for irregular cutouts of field size 6.5 Χ 9 cm
2
and 11.5 Χ 15 cm
2
for beam energies ranging from 6 to 20 MeV. The PDD, beam flatness, symmetry and uniformity index were compared. For lower energy (6 MeV), there was no change in the depth of maximum dose (R100) as SSD increased, but for higher energy (20 MeV), the R
100
depth increased from 2 cm to 3 cm as SSD increased. This shows that as SSD increases there is an increase in the depth of the maximum dose for higher energy beams. There is a +7 mm shift in the R
100
depth when compared with regular and irregular field sizes. The symmetry was found to be within limits for all the field sizes as the treatment distance extended as per International Electro technical Commision (IEC) protocol. There was a loss of beam flatness for irregular fields and it was more pronounced for lower energies as compared with higher energies, so that the clinically useful isodose level (80% and 90%) width decreases with increase in SSD. This suggests that target coverage at extended SSD with irregular cut-outs may be inadequate unless relatively large fields are used.
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TECHNICAL NOTES
Spatial distribution of gamma radiation levels in surface soils from Jaduguda uranium mineralization zone, Jharkhand, India, using
γ
-ray spectrometry, and determination of outdoor dose to the population
Mandakini Maharana, Narayani Krishnan, D Sengupta
October-December 2010, 35(4):235-241
DOI
:10.4103/0971-6203.71762
PMID
:21170189
The concentrations of natural radionuclides in surface soil samples around selected villages of Jaduguda were investigated and compared with the radioactivity level in the region. Concentrations of
238
U,
232
Th, and
40
K were determined by a gamma ray spectrometer using the HPGe detector with 50% relative efficiency, and the radiation dose to the local population was estimated. The average estimated activity concentrations of
238
U,
232
Th, and
40
K in the surface soil were 53.8, 44.2 and 464.2 Bq kg
-1
respectively. The average absorbed dose rate in the study area was estimated to be 72.5 nGy h-1, where as the annual effective dose to the population was 0.09 mSv y-1. A correlation analysis was made between measured dose rate and individual radionuclides, in order to delineate the contribution of the respective nuclides towards dose rate. The radio-elemental concentrations of uranium, thorium and potassium estimated for the soils, in the study area, indicated the enrichment of uranium series nuclide. The results of the present study were subsequently compared with international and national recommended values.
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8,015
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EDITORIAL
A concern on in-phantom photon energy response of luminescence dosimeters for clinical applications
AS Pradhan
October-December 2010, 35(4):187-188
DOI
:10.4103/0971-6203.71756
PMID
:21170181
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ORIGINAL ARTICLES
Implementation and validation of a commercial portal dosimetry software for intensity-modulated radiation therapy pre-treatment verification
C Varatharaj, Eugenia Moretti, M Ravikumar, Maria Rosa Malisan, Sanjay S Supe, Renato Padovani
October-December 2010, 35(4):189-196
DOI
:10.4103/0971-6203.71758
PMID
:21170182
Electronic portal imaging devices (EPIDs) are extensively used for obtaining dosimetric information of pre-treatment field verification and
in-vivo
dosimetry for intensity-modulated radiotherapy (IMRT). In the present study, we have implemented the newly developed portal dosimetry software using independent dose prediction algorithm EPIDose
TM
and evaluated this new tool for the pre-treatment IMRT plan quality assurance of Whole Pelvis with Simultaneous Integrated Boost (WP-SIB-IMRT ) of prostate cases by comparing with routine two-dimensional (2D) array detector system (MapCHECK
TM
). We have investigated 104 split fields using g-distributions in terms of predefined g frequency parameters. The mean γ values are found to be 0.42 (SD: 0.06) and 0.44 (SD: 0.06) for the EPIDose and MapCHECK
TM
, respectively. The average g∆ for EPIDose and MapCHECK
TM
are found as 0.51 (SD: 0.06) and 0.53 (SD: 0.07), respectively. Furthermore, the percentage of points with g < 1, γ < 1.5, and γ > 2 are 97.4%, 99.3%, and 0.56%, respectively for EPIDose and 96.4%, 99.0% and 0.62% for MapCHECK
TM
. Based on our results obtained with EPIDose and strong agreement with MapCHECK
TM
, we may conclude that the EPIDose portal dosimetry system has been successfully implemented and validated with our routine 2D array detector
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NEWS
News
October-December 2010, 35(4):247-248
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ORIGINAL ARTICLES
Dose-volume histogram quality assurance for linac-based treatment planning systems
Michael S Gossman, Morris I Bank
October-December 2010, 35(4):197-201
DOI
:10.4103/0971-6203.71759
PMID
:21170183
Dose-volume histograms provide key information to radiation oncologists when they assess the adequacy of a patient treatment plan in radiation therapy. It is important therefore that all clinically relevant data be accurate. In this article we present the first quality assurance routine involving a direct comparison of planning system results with the results obtained from independent hand calculations. Given a known three-dimensional (3-D) structure such as a parallelepiped, a simple beam arrangement, and known physics beam data, a time-efficient and reproducible method for verifying the accuracy of volumetric statistics (DVH) from a radiation therapy treatment planning system (TPS) can be employed rapidly, satisfying the QA requirements for (TPS) commissioning, upgrades, and annual checks. Using this method, the maximum disagreement was only 1.7% for 6 MV and 1.3% for 18 MV photon energies. The average accuracy was within 0.6% for 6 MV and 0.4% for 18 MV for all depth-dose results. A 2% disagreement was observed with the treatment planning system DVH from defined volume comparison to the known structure dimensions.
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Effect of various physical parameters on surface and build-up dose for 15-MV X-rays
Girigesh Yadav, RS Yadav, Alok Kumar
October-December 2010, 35(4):202-206
DOI
:10.4103/0971-6203.71761
PMID
:21170184
The purpose of this study was to find out the effect of various physical parameters on the skin and build-up doses of 15-MV photon beams. The effects of field dimensions, acrylic shadow tray, focus to-skin distance (FSD) on surface and buildup dose were determined for open, motorized 60° wedge (MW) and blocked fields. A 'Markus' plane parallel plate chamber was used for these measurements in an Elekta (6-15MV) linear accelerator. The surface dose for MW fields was lower than the dose for an open field, but the trend reversed for large fields and higher degree wedges. With the use of an acrylic shadow tray, the surface dose increased for all field sizes, but the increase was dominant for large fields. The surface dose for blocked fields was lower than the dose for open fields. The percentage depth dose of 10 Χ 10 cm
2
field at surface (PDD
0
) for open beam were 13.89%, 11.71%, and 10.74% at 80 cm, 100 cm, and 120 cm FSD, respectively. The blocking tray increased PDD
0
of 10 Χ 10 cm
2
field to 26.29%, 14.01%, and 11.53%, while the motorized 60° wedge decreased PDD
0
to 11.32%, 9.7%, and 8.9 % at these FSDs. The maximum PDD difference seen at surface (i.e., skin) for 5 Χ 5 cm
2
, 15 Χ 15 cm
2
, and 30 Χ 30 cm
2
are 0.5%, 4.6%, and 5.6% for open field and 0.9%, 4.7%, and 7.2% for motorized 60 wedge field, when FSDs varied from 80 cm to 120 cm. The maximum PDD difference seen at surface for 5 Χ 5 cm
2
, 15 Χ 15 cm
2
, and 30 Χ 30 cm
2
fields are 5.6%, 22.8%, and 29.6%, respectively, for a 1.0-cm perspex-blocking tray as the FSD is changed. The maximum PDD difference was seen at the surface (i.e., skin) and this decreased with increasing depth.
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Radiological safety status and quality assurance audit of medical X-ray diagnostic installations in India
AU Sonawane, Meghraj Singh, J. V. K. Sunil Kumar, Arti Kulkarni, VK Shirva, AS Pradhan
October-December 2010, 35(4):229-234
DOI
:10.4103/0971-6203.71764
PMID
:21170188
We conducted a radiological safety and quality assurance (QA) audit of 118 medical X-ray diagnostic machines installed in 45 major hospitals in India. The main objective of the audit was to verify compliance with the regulatory requirements stipulated by the national regulatory body. The audit mainly covered accuracy check of accelerating potential (kVp), linearity of tube current (mA station) and timer, congruence of radiation and optical field, and total filtration; in addition, we also reviewed medical X-ray diagnostic installations with reference to room layout of X-ray machines and conduct of radiological protection survey. A QA kit consisting of a kVp Test-O-Meter (ToM) (Model RAD/FLU-9001), dose Test-O-Meter (ToM) (Model 6001), ionization chamber-based radiation survey meter model Gun Monitor and other standard accessories were used for the required measurements. The important areas where there was noncompliance with the national safety code were: inaccuracy of kVp calibration (23%), lack of congruence of radiation and optical field (23%), nonlinearity of mA station (16%) and timer (9%), improper collimator/diaphragm (19.6%), faulty adjustor knob for alignment of field size (4%), nonavailability of warning light (red light) at the entrance of the X-ray room (29%), and use of mobile protective barriers without lead glass viewing window (14%). The present study on the radiological safety status of diagnostic X-ray installations may be a reasonably good representation of the situation in the country as a whole. The study contributes significantly to the improvement of radiological safety by the way of the steps already taken and by providing a vital feed back to the national regulatory body.
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