Journal of Medical Physics
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   2008| January-March  | Volume 33 | Issue 1  
    Online since March 6, 2008

 
 
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ORIGINAL ARTICLES
Dosimetric evaluation of rectum and bladder using image-based CT planning and orthogonal radiographs with ICRU 38 recommendations in intracavitary brachytherapy
Swamidas V Jamema, Sherly Saju, Umesh Mahantshetty, S Pallad, DD Deshpande, SK Shrivastava, KA Dinshaw
January-March 2008, 33(1):3-8
DOI:10.4103/0971-6203.39417  PMID:20041045
The purpose is to compare CT-based dosimetry with International Commission on Radiation Units and Measurements (ICRU 38) bladder and rectum reference points in patients of carcinoma of uterine cervix treated with intracavitary brachytherapy (ICA). Twenty-two consecutive patients were evaluated. Orthogonal radiographs and CT images were acquired and transferred to PLATO planning system. Bladder and rectal reference points were identified according to ICRU 38 recommendations. Dosimetry was carried out based on Manchester system. Patient treatment was done using 192 Iridium high dose rate (HDR) remote after-loading machine based on the conventional radiograph-based dosimetry. ICRU rectal and bladder point doses from the radiograph plans were compared with D 2 , dose received by 2 cm 3 of the organ receiving maximum dose from CT plan. V 2 , volume of organ receiving dose more than the ICRU reference point, was evaluated. The mean (±standard deviation) volume of rectum and bladder was 60 (±28) cm 3 and 138 (±41) cm 3 respectively. The mean reference volume in radiograph and CT plan was 105 (±7) cm 3 and 107 (±7) cm 3 respectively. It was found that 6 (±4) cm3 of rectum and 16 (±10) cm 3 of bladder received dose more than the prescription dose. V2 of rectum and bladder was 7 (±1.7) cm 3 and 20.8 (±6) cm 3 respectively. Mean D 2 of rectum and bladder was found to be 1.11 (±0.2) and 1.56 (±0.6) times the mean ICRU reference points respectively. This dosimteric study suggests that comparison of orthogonal X-ray-based and CT-based HDR ICA planning is feasible. ICRU rectal point dose correlates well with maximum rectal dose, while ICRU bladder point underestimates the maximum bladder dose.
  8 5,484 658
Application of small-angle X-ray scattering for differentiation among breast tumors
V Changizi, A Arab Kheradmand, MA Oghabian
January-March 2008, 33(1):19-23
DOI:10.4103/0971-6203.39420  PMID:20041048
Small-angle X-ray scattering (SAXS) is an X-ray diffraction-based technique where a narrow collimated beam of X-rays is focused onto a sample and the scattered X-rays recorded by a detector. The pattern of the scattered X-rays carries information on the molecular structure of the material. As breast cancer is the most widespread cancer in women and differentiation among its tumors is important, this project compared the results of coherent X-ray scattering measurements obtained from benign and malignant breast tissues. The energy-dispersive method with a setup including X-ray tube, primary collimator, sample holder, secondary collimator and high-purity germanium (HpGe) detector was used. One hundred thirty-one breast-tissue samples, including normal, fibrocystic changes and carcinoma, were studied at the 6° scattering angle. Diffraction profiles (corrected scattered intensity versus momentum transfer) of normal, fibrocystic changes and carcinoma were obtained. These profiles showed a few peak positions for adipose (1.15 ± 0.06 nm -1 ), mixed normal (1.15 ± 0.06 nm -1 and 1.4 ± 0.04 nm -1 ), fibrocystic changes (1.46 ± 0.05 nm -1 and 1.74 ± 0.04 nm -1 ) and carcinoma (1.55 ± 0.04 nm -1 , 1.73 ± 0.06 nm -1 , 1.85 ± 0.05 nm -1 ). We were able to differentiate between normal, fibrocystic changes (benign) and carcinoma (malignant) breast tissues by SAXS. However, we were unable to differentiate between different types of carcinoma.
  7 4,426 355
Dosimetry and treatment planning of Occu-Prosta I-125 seeds for intraocular lesions
Suresh Chaudhari, Sudesh Deshpande, Vivek Anand, Sandeep De, Sanjay Saxena, A Dash, Mahua Basu, Preetam Samant, V Kannan
January-March 2008, 33(1):14-18
DOI:10.4103/0971-6203.39419  PMID:20041047
Intraocular malignant lesions are frequently encountered in clinical practice. Plaque brachytherapy represents an effective means of treatment for intraocular lesions. Recently Radiopharmaceutical Division, BARC, Mumbai, has indigenously fabricated reasonable-cost I-125 sources. Here we are presenting the preliminary experience of dosimetry of sources, configuration of treatment planning system (TPS) and quality assurance (QA) for eye plaque therapy with Occu-Prosta I-125 seeds, treated in our hospital, for a patient with ocular lesions. I-125 seeds were calibrated using well-type chamber. BrachyVision TPS was configured with Monte Carlo computed radial dose functions and anisotropy functions for I-125 sources. Dose calculated by TPS at different points in central axis and off axis was compared with manually calculated dose. Eye plaque was fabricated of 17 karat pure gold, locally. The seeds were arranged in an outer ring near the edge of the plaque and in concentric rings throughout the plaque. The sources were manually digitized on the TPS, and dose distribution was calculated in three dimensions. Measured activity using cross-calibrated well-type chamber was within ±10% of the activity specified by the supplier. Difference in TPS-calculated dose and manually calculated dose was within 5%. Treatment time calculated by TPS was in concordance with published data for similar plaque arrangement.
  4 4,332 354
EDITORIAL
Quality of high-energy X-ray radiotherapy beams: Issues of adequacy of routine experimental verification
SD Sharma
January-March 2008, 33(1):1-2
DOI:10.4103/0971-6203.39416  PMID:20041044
  3 7,848 754
ORIGINAL ARTICLES
A new approach to position reconstruction in TOFPET
Nagendra Nath Mondal
January-March 2008, 33(1):9-13
DOI:10.4103/0971-6203.39418  PMID:20041046
Monte Carlo Simulation (MCS) is a state-of-the-art technique in designing sophisticated apparatus for various applications in science and technology. We adopted MCS based on GEANT (GEometry ANd Tracking) in order to design a simple time-of-flight positron emission tomography (TOFPET). In MCS studies, a new method of position reconstruction of positron-electron annihilation points has been developed so far. Simulation results show that this technique may not be useful for small animal imaging camera but might be practicable in diagnostic TOFPET camera. Specific issue of this simulation technique is discussed.
  1 3,638 334
TECHNICAL NOTES
Solid water phantom heat conduction: Heating and cooling rates
Martin J Butson, Tsang Cheung, Peter K.N Yu
January-March 2008, 33(1):24-28
DOI:10.4103/0971-6203.39421  PMID:20041049
Solid water is often the phantom material of choice for dosimetry procedures in radiotherapy high-energy X-ray and electron beam radiation calibration and quality assurance. This note investigates variation in heat conduction that can occur for a common commercially available solid water stack phantom when a temperature differential occurs between the phantom and ambient temperature. These variations in temperature can then affect radiation measurements and thus the accuracy of radiation dosimetry. In this manuscript, we aim to investigate the variations in temperature which can occur in radiation measurement incorporated (RMI) solid water phantoms, their thermal properties and the effects on radiation dosimetry which can occur because of temperature differentials. Results have shown that the rate of temperature change at a phantom center is a complex function but appears relatively proportional to the surface area of the phantom in normal clinical usage. It is also dependent on the thermal conductivity of any material in contact with the phantom; and the nature of the phantom construction, i.e., the number and thickness of slices within the phantom. A thermal time constant of approximately 20 min was measured for a 2-cm solid water phantom slice when located on a steel workbench in comparison to 60 min when located on a wooden workbench (linac couch insert). It is found that for larger solid water stack phantoms, a transient (within 1°C) thermal equilibrium exists at the center for up to 2 h, before the temperature begins to change. This is assumed to be due to the insulating properties of multiple slices within the stack, whereby very small air spaces are introduced inhibiting the heat conduction through the phantom material. It is therefore recommended that the solid water/phantom material is kept within the treatment room for closest thermal accuracy conditions or at least placed within the room approximately 10 h before dosimetry measurements. If these options are not available, a standard linear interpolation method for calculation of temperature should be used to minimize uncertainty of temperature measurements.
  1 4,568 251
Pediatric radiography entrance doses for some routine procedures in three hospitals within eastern Nigeria
NO Egbe, SO Inyang, OB Ibeagwa, NO Chiaghanam
January-March 2008, 33(1):29-34
DOI:10.4103/0971-6203.39422  PMID:20041050
A survey of the entrance surface doses in the routine radiography of children in eastern Nigeria has been carried out in three hospitals, using thermoluminescence detectors. Chest, abdomen, lumbar spine, skull and pelvis were covered in this study. Findings reveal that doses are higher than the recommended reference values elsewhere, as well as values reported for Sudan. The mean percentage difference in entrance doses for chest radiography for this study and an earlier one carried out for three hospitals in the west of Nigeria is about 44.7%. The high doses are traceable to a lack of standardization in procedure, resulting in use of low tube voltages and high currents for examination, as well as the status of facilities in the area. Recommendations are made for immediate corrective measures to lower the doses.
  1 4,526 317
BOOK REVIEWS
A Ph.D. thesis entitled "Dose audit and optimization for radiological and interventional procedures"
Keith Faulkner
January-March 2008, 33(1):35-35
  - 2,614 312
A Ph.D. thesis entitled "Dosimetric studies on Hi-Tech Radiotherapy Systems and Sources and Development of Quality Assurance/ Audit Programmes"
AS Pradhan
January-March 2008, 33(1):36-37
  - 3,532 477
 
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