Journal of Medical Physics
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   2008| July-September  | Volume 33 | Issue 3  
    Online since September 4, 2008

 
 
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REVIEW ARTICLE
Recent developments of optically stimulated luminescence materials and techniques for radiation dosimetry and clinical applications
AS Pradhan, JI Lee, JL Kim
July-September 2008, 33(3):85-99
DOI:10.4103/0971-6203.42748  PMID:19893698
During the last 10 years, optically stimulated luminescence (OSL) has emerged as a formidable competitor not only to thermoluminescence dosimetry (TLD) but also to several other dosimetry systems. Though a large number of materials have been synthesized and studied for OSL, Al 2 O 3 :C continues to dominate the dosimetric applications. Re-investigations of OSL in BeOindicate that this material might provide an alternative to Al 2 O 3 :C. Study of OSL of electronic components of mobile phones and ID cards appears to have opened up a feasibility of dosimetry and dose reconstruction using the electronic components of gadgets of everyday use in the events of unforeseen situations of radiological accidents, including the event of a dirty bomb by terrorist groups. Among the newly reported materials, a very recent development of NaMgF 3 :Eu 2+ appears fascinating because of its high OSL sensitivity and tolerable tissue equivalence. In clinical dosimetry, an OSL as a passive dosimeter could do all that TLD can do, much faster with a better or at least the same efficiency; and in addition, it provides a possibility of repeated readout unlike TLD, in which all the dose information is lost in a single readout. Of late, OSL has also emerged as a practical real-time dosimeter for in vivo measurements in radiation therapy (for both external beams and brachytherapy) and in various diagnostic radiological examinations including mammography and CT dosimetry. For in vivo measurements, a probe of Al 2 O 3 :C of size of a fraction of a millimeter provides the information on both the dose rate and the total dose from the readout of radioluminescence and OSL signals respectively, from the same probe. The availability of OSL dosimeters in various sizes and shapes and their performance characteristics as compared to established dosimeters such as plastic scintillation dosimeters, diode detectors, MOSFET detectors, radiochromic films, etc., shows that OSL may soon become the first choice for point dose measurements in clinical applications. A brief review of the recent developments is presented.
  28 8,994 792
ORIGINAL ARTICLES
Segmentation and classification of medical images using texture-primitive features: Application of BAM-type artificial neural network
Neeraj Sharma, Amit K Ray, Shiru Sharma, KK Shukla, Satyajit Pradhan, Lalit M Aggarwal
July-September 2008, 33(3):119-126
DOI:10.4103/0971-6203.42763  PMID:19893702
The objective of developing this software is to achieve auto-segmentation and tissue characterization. Therefore, the present algorithm has been designed and developed for analysis of medical images based on hybridization of syntactic and statistical approaches, using artificial neural network (ANN). This algorithm performs segmentation and classification as is done in human vision system, which recognizes objects; perceives depth; identifies different textures, curved surfaces, or a surface inclination by texture information and brightness. The analysis of medical image is directly based on four steps: 1) image filtering, 2) segmentation, 3) feature extraction, and 4) analysis of extracted features by pattern recognition system or classifier. In this paper, an attempt has been made to present an approach for soft tissue characterization utilizing texture-primitive features with ANN as segmentation and classifier tool. The present approach directly combines second, third, and fourth steps into one algorithm. This is a semisupervised approach in which supervision is involved only at the level of defining texture-primitive cell; afterwards, algorithm itself scans the whole image and performs the segmentation and classification in unsupervised mode. The algorithm was first tested on Markov textures, and the success rate achieved in classification was 100%; further, the algorithm was able to give results on the test images impregnated with distorted Markov texture cell. In addition to this, the output also indicated the level of distortion in distorted Markov texture cell as compared to standard Markov texture cell. Finally, algorithm was applied to selected medical images for segmentation and classification. Results were in agreement with those with manual segmentation and were clinically correlated.
  26 13,123 721
TECHNICAL NOTE
A method for estimation of accuracy of dose delivery with dynamic slit windows in medical linear accelerators
R Ravichandran, JP Binukumar, SS Sivakumar, K Krishnamurthy, CA Davis
July-September 2008, 33(3):127-129
DOI:10.4103/0971-6203.42768  PMID:19893703
Intensity-modulated radiotherapy (IMRT) clinical dose delivery is based on computer-controlled multileaf movements at different velocities. To test the accuracy of modulation of the beam periodically, quality assurance (QA) methods are necessary. Using a cylindrical phantom, dose delivery was checked at a constant geometry for sweeping fields. Repeated measurements with an in-house designed methodology over a period of 1 year indicate that the method is very sensitive to check the proper functioning of such dose delivery in medical linacs. A cylindrical perspex phantom with facility to accurately position a 0.6-cc (FC 65) ion chamber at constant depth at isocenter, (SA 24 constancy check tool phantom for MU check, Scanditronix Wellhofer) was used. Dosimeter readings were integrated for 4-mm, 10-mm, 20-mm sweeping fields and for 3 angular positions of the gantry periodically. Consistency of standard sweeping field output (10-mm slit width) and the ratios of outputs against other slit widths over a long period were reported. A 10-mm sweeping field output was found reproducible within an accuracy of 0.03% (n = 25) over 1 year. Four-millimeter, 20-mm outputs expressed as ratio with respect to 10-mm sweep output remained within a mean deviation of 0.2% and 0.03% respectively. Outputs at 3 gantry angles remained within 0.5%, showing that the effect of dynamic movements of multileaf collimator (MLC) on the output is minimal for angular positions of gantry. This method of QA is very simple and is recommended in addition to individual patient QA measurements, which reflect the accuracy of dose planning system. In addition to standard output and energy checks of linacs, the above measurements can be complemented so as to check proper functioning of multileaf collimator for dynamic field dose delivery.
  3 2,142 230
ORIGINAL ARTICLES
Design of mini phantom and measurement of cobalt-60 beam data parameters
S Senthilkumar, V Ramakrishnan
July-September 2008, 33(3):100-107
DOI:10.4103/0971-6203.42750  PMID:19893699
Low cost mini phantoms were fabricated indigenously with different water equivalent material such as polymethyl methacrylate and Bee's wax of different shapes (with dome top surface and flat top surface). The beam parameters of the Co-60 machine, such as head scatter correction factor (S h ), phantom scatter correction factor (S P ), total scatter correction factor (S C,P ), collimator exchange effect were measured. Output ratio measurements were taken for both mini phantom and water phantom for different square and rectangular field sizes. Normalized output ratios were compared with ESTRO published values and (Storchi and Van Gasteren) S and G data. The percentage of variation between the measured and the literature values is about 0.7%. Collimator exchange effect were measured for water and mini phantom for different field size, were compared with ESTRO value. This was found to be 0.5% and 1.0% respectively. Phantom scatter correction factors were calculated for square and rectangular filed sizes; this was compared with ESTRO values, found to be 0.7% for square and 1.0% for rectangular filed size. It was also noted that there were no appreciable variation observed in ion chamber readings of different materials of mini phantoms for dome and flat surfaces. Mini phantom measurements were done for all types of phantoms and the measured values were compared with the existing data and they were in good agreement with the published values.
  2 3,889 505
Dosimetric evaluation of 120-leaf multileaf collimator in a Varian linear accelerator with 6-MV and 18-MV photon beams
R Mohan, K Jayesh, RC Joshi, Maha Al-idrisi, P Narayanamurthy, Saroj Kumar Das Majumdar
July-September 2008, 33(3):114-118
DOI:10.4103/0971-6203.42757  PMID:19893701
In this study the dosimetric characteristics of 120-leaf multileaf collimators (MLCs) were evaluated for 6-MV and 18-MV photon beams. The dose rate, percentage depth dose, surface dose, dose in the build-up region, beam profile, flatness, symmetry, and penumbra width were measured using three field-defining methods: (i) 'Jaw only', (ii) 'MLC only', and (iii) 'MLC+Jaw'. Analysis of dose rate shows that the dose rate for 'MLC only' field was higher than that for 'Jaw only'' and 'MLC+Jaw' fields in both the energies. The 'percentage of difference' of dose rates between 'MLC only' and 'MLC+Jaw' was (0.9% to 4.4%) and (1.14% to 7%) for 6 MV and 18 MV respectively. The surface dose and dose in the build-up region were more pronounced for 'MLC only' fields for both energies, and no significant difference was found in percentage depth dose beyond dmax for both energies. Beam profiles show that flatness and symmetry for both the energies were less than the 3%. The penumbra width for 'MLC only' field was more than that for the other two field-defining methods by (1 to 2 mm) and (0.8 to 1.3 mm) for 6-MV and 18-MV photon beams respectively. Analysis of 'width of 50% dose level' of the beam profiles at dmax to reflect the field size shows 1 to 2 mm more for 6-MV photons and 2.2 to 2.4 mm morefor 18-MV photons for 'MLC only' fields. The results of this study suggest that the characteristics of 120-leaf MLC system with 6 MV and 18 MV are same in all aspects except the surface dose, penumbra, dose in the build-up region, and width of 50% dose levels.
  2 4,747 529
EDITORIAL
Need of independent dose verification in brachytherapy
A Shanta
July-September 2008, 33(3):83-84
DOI:10.4103/0971-6203.42743  PMID:19893697
  1 2,182 397
ORIGINAL ARTICLES
Absolute dose determination in high-energy electron beams: Comparison of IAEA dosimetry protocols
S Sathiyan, M Ravikumar
July-September 2008, 33(3):108-113
DOI:10.4103/0971-6203.42754  PMID:19893700
In this study, absorbed doses were measured and compared for high-energy electrons (6, 9, 12, 16, and 20 MeV) using International Atomic Energy Agency (IAEA), Technical Reports Series No. 277 (TRS), TRS 381, and TRS 398 dosimetry protocols. Absolute dose measurements were carried out using FC65-G Farmer chamber and Nordic Association of Clinical Physicists (NACP) parallel plate chamber with DOSE1 electrometer in WP1-D water phantom for reference field size of 15 x 15 cm 2 at 100 cm source-to-surface distance. The results show that the difference between TRS 398 and TRS 381 was about 0.24% to 1.3% depending upon the energy, and the maximum difference between TRS 398 and TRS 277 was 1.5%. The use of cylindrical chamber in electron beam gives the maximum dose difference between the TRS 398 and TRS 277 in the order of 1.4% for energies above 10 MeV (R 50 > 4 g/cm 2 ). It was observed that the accuracy of dose estimation was better with the protocols based on the water calibration procedures, as no conversion quantities are involved for conversion of dose from air to water. The cross-calibration procedure of parallel plate chamber with high-energy electron beams is recommended as it avoids p wall correction factor entering into the determination of k Q,Qo .
  1 5,192 540
BOOK REVIEW
The handbook of physics in diagnostic imaging
KN Govinda Rajan
July-September 2008, 33(3):130-131
  - 2,697 398
NEWS AND EVENTS
News and Events
T Ganesh
July-September 2008, 33(3):132-134
PMID:19893704
  - 1,655 119
 
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