Journal of Medical Physics
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   2007| October-December  | Volume 32 | Issue 4  
    Online since December 28, 2007

 
 
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ORIGINAL ARTICLES
Whole-body PET acceptance test in 2D and 3D using NEMA NU 2-2001 protocol
Shamurailatpam Dayananda Sharma, R Prasad, Bina Shetye, V Rangarajan, D Deshpande, SK Shrivastava, KA Dinshaw
October-December 2007, 32(4):150-155
DOI:10.4103/0971-6203.37479  PMID:21224924
Integrated PET/CT has emerged as an integral component of oncology management because of its unique potential of providing both functional and morphological images in a single imaging session. In this work, performance of the 'bismuth germinate (BGO) crystal'-based PET of a newly installed Discovery ST PET/CT was evaluated in 2D and 3D mode for whole-body scanning using National Electrical Manufacturers Association (NEMA) NU 2-2001 protocol and the recommended phantoms. During the entire measurements, the system operates with an energy window of 375-650 keV and 11.7 ns coincidence time window. The set of tests performed were spatial resolution, sensitivity, scatter fraction (SF) and counting rate performance. The average transaxial and axial spatial resolution measured as full width at half maximum (FWHM) of the point spread function at 1 cm (and 10 cm) off-axis was 0.632 (0.691) and 0.491 (0.653) cm in 2D and 0.646 (0.682) and 0.54 (0.601) cm in 3D respectively. The average sensitivity for the two radial positions ( R = 0 cm and R = 10 cm) was 2.56 (2.63) cps/kBq in 2D and 11.85 (12.14) cps/kBq in 3D. The average scatter fraction was 19.79% in 2D and 46.19% in 3D. The peak noise equivalent counting rate (NECR) evaluated with single random subtraction was 89.41 kcps at 49 kBq/cc in 2D and 60 kcps at 12 kBq/cc in 3D acquisition mode. The NECR with delayed random subtraction was 61.47 kcps at 40.67 kBq/cc in 2D and 45.57 kcps at 16.45 kBq/cc in 3D. The performance of the PET scanner was satisfactory within the manufacturer-specified limits. The test result of PET shows excellent system sensitivity with relatively uniform resolution throughout the FOV, making this scanner highly suitable for whole-body studies.
  6,210 548 1
Assessment of bone mineral density by DXA and the trabecular microarchitecture of the calcaneum by texture analysis in pre- and postmenopausal women in the evaluation of osteoporosis
R Karunanithi, S Ganesan, T.M.R Panicker, M Paul Korath, K Jagadeesan
October-December 2007, 32(4):161-168
DOI:10.4103/0971-6203.37481  PMID:21224926
The in vivo evaluation of trabecular bone structure could be useful in the diagnosis of osteoporosis for the characterization of therapeutic response and understanding the role of parameters other than bone mineral density (BMD) in defining skeletal status. This study was made to evaluate changes taking place in the trabecular architecture of bone with age and menopausal status in women. The findings are compared with the femoral neck bone as well as the trochantar bone mineral density determined by dual energy X-ray absorptiometry (DXA), which is a standard reference test for evaluation of osteoporosis. Seventy females were recruited for the study, 25 pre-menopausal (mean age SD: 39.4 3.8) and 45 postmenopausal (mean age SD: 57.9 7.9) women. The right femoral neck bone mineral density was measured for them by dual energy X-ray absorptiometry (DXA). For the same individuals, lateral view radiographs of the right calcaneum were taken as well. The radiographs were digitized and the region of interest (ROI) of 256 256 pixels was selected, the run-length matrix was computed for calculating seven parameters [Table 1] and the two-dimensional fast Fourier transform of the image was calculated. Using the FFT, the power spectral density (PSD) was derived and the root mean square (RMS) value was determined. Our results confirm that age has a significant influence on the texture of the trabecular bone and bone mineral density.
  5,064 349 2
Dosimetry and verification of 60Co total body irradiation with human phantom and semiconductor diodes
Mahmoud Allahverdi, Ghazale Geraily, Mahbod Esfehani, Aliakbar Sharafi, Peyman Haddad, Alireza Shirazi
October-December 2007, 32(4):169-174
DOI:10.4103/0971-6203.37482  PMID:21224927
Total Body Irradiation (TBI) is a form of radiotherapy used for patients prior to bone marrow or stem cell transplant to destroy any undetectable cancer cells. The dosimetry characteristics of a 60 Co unit for TBI were studied and a simple method for the calculation of the prescribed dose for TBI is presented. Dose homogeneity was verified in a human phantom. Dose measurements were made in water phantom (30 30 30 cm 3 ), using farmer ionization chamber (0.6 cc, TM30010, PTW) and a parallel plate ionization chamber (TM23343, PTW). Point dose measurements for AP/PA irradiation were measured in a human phantom using silicon diodes (T60010L, PTW). The lung dose was measured with an ionization chamber (0.3 cc, TM31013). The validity of the proposed algorithm was checked at TBI distance using the human phantom. The accuracy of the proposed algorithm was within 3.5%. The dose delivered to the mid-lobe of the lung was 14.14 Gy and it has been reduced to 8.16 Gy by applying the proper shield. Dose homogeneity was within 7% for all measured points. The results indicate that a good agreement between the total prescribed and calculated midplane doses can be achieved using this method. Therefore, it could be possible to use calculated data for TBI treatments.
  3,812 384 3
Optimization and audit of radiation dose during percutaneous transluminal coronary angioplasty
Roshan S Livingstone, BS Timothy Peace, Sunil Chandy, Paul V George, Purendra Pati
October-December 2007, 32(4):145-149
DOI:10.4103/0971-6203.37478  PMID:21224923
The percutaneous transluminal coronary angioplasty (PTCA) is one of the interventional procedures which impart high radiation doses to patients compared to the other cardiologic procedures. This study intends to audit and optimize radiation dose imparted to patients undergoing PTCA. Forty-four patients who underwent PTCA involving single or multiple stent placement guided under cardiovascular X-ray machine were included in the study. Radiation doses were measured using dose area product (DAP) meter for patients undergoing single and multiple stent placements during PTCA. A dose reduction of 27-47% was achieved using copper filters and optimal exposure parameters. The mean DAP values before optimization were 66.16 and 122.68 Gy cm 2 for single and multiple stent placement respectively. These values were 48.67 and 65.44 Gy cm 2 respectively after optimization. In the present scenario, due to the increase in the number of PTCAs performed and the associated risk from radiation, periodical audit of radiation doses for interventional procedures are recommended.
  3,821 293 4
Optimized point dose measurement: An effective tool for QA in intensity-modulated radiotherapy
Alok Kumar, Gautam Mukherjee, Girigesh Yadav, Vinod Pandey, Kalyan Bhattacharya
October-December 2007, 32(4):156-160
DOI:10.4103/0971-6203.37480  PMID:21224925
In some cases of Intensity-modulated radiotherapy (IMRT) point dose measurement, there exists significant deviation between calculated and measured dose at isocenter, sometimes greater than 3%. This may be because IMRT fields generate complex profiles at the reference point. The deviation arises due to lack of lateral electronic equilibrium for small fields, and other factors such as leakage and scatter contribution. Measurements were done using 0.125-cc ion chamber and Universal IMRT phantom (both from PTW-Freiburg). The aim is to find a suitable point of measurement for the chamber to avoid discrepancy between calculated and measured dose. Various beam profiles were generated in the plane of the chamber for each field by implementing patient plan on the IMRT phantom. The profiles show that for the fields which are showing deviation, the ion chamber lies in the steep-gradient region. To rectify the problem, the TPS (Treatment Planning System) calculated dose is found out at various points in the measurement plane of the chamber at isocenter. The necessary displacement to the chamber, as noted from the TPS, was given to obtain the optimum result. Twenty cases were studied for optimization, whose percentage deviation was more than 3%. The results were well within tolerance criteria of 3% after optimization. The mean percentage deviation value for the 20 cases studied, with standard deviation of 2.33 under 95% confidence interval, was found out to be 2.10% 1.14. Those cases that have significant variation even after optimization are further studied with film dosimetry.
  3,485 517 1
GUEST EDITORIAL
A concern about plagiarism
William R Hendee
October-December 2007, 32(4):143-144
DOI:10.4103/0971-6203.37477  PMID:21224922
  3,573 292 4
ORIGINAL ARTICLES
Computer simulations and models for the performance characteristics of spectrally equivalent X-ray beams in medical diagnostic radiology
Akintunde A Okunade
October-December 2007, 32(4):175-184
DOI:10.4103/0971-6203.37483  PMID:21224928
In order to achieve uniformity in radiological imaging, it is recommended that the concept of equivalence in shape (quality) and size (quantity) of clinical X-ray beams should be used for carrying out the comparative evaluation of image and patient dose. When used under the same irradiation geometry, X-ray beams that are strictly or relatively equivalent in terms of shape and size will produce identical or relatively identical image quality and patient dose. Simple mathematical models and software program EQSPECT.FOR were developed for the comparative evaluation of the performance characteristics in terms of contrast (C), contrast-to-noise ratio (CNR) and figure-of-merit (FOM = CNR 2 /DOSE) for spectrally equivalent beams transmitted through filter materials referred to as conventional and k-edged. At the same value of operating potential (kVp), results show that spectrally equivalent beam transmitted through conventional filter with higher atomic number ( Z -value) in comparison with that transmitted through conventional filter with lower Z -value resulted in the same value of C and FOM. However, in comparison with the spectrally equivalent beam transmitted through filter of lower Z -value, the beam through filter of higher Z -value produced higher value of CNR and DOSE at equal tube loading (mAs) and kVp. Under the condition of equivalence of spectrum, at scaled (or reduced) tube loading and same kVp, filter materials of higher Z -values can produce the same values of C, CNR, DOSE and FOM as filter materials of lower Z -value. Unlike the case of comparison of spectrally equivalent beam transmitted through one conventional filter and that through another conventional filter, it is not possible to derive simple mathematical formulations for the relative performance of spectrally equivalent beam transmitted through a given conventional filter material and that through k-edge filter material.
  3,342 227 -
NEWS
News
T Ganesh
October-December 2007, 32(4):185-188
  2,188 208 -
 
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