Journal of Medical Physics
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   2007| July-September  | Volume 32 | Issue 3  
 
 
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ORIGINAL ARTICLES
Initial experience with an 11 MeV self-shielded medical cyclotron on operation and radiation safety
GS Pant, S Senthamizhchelvan
July-September 2007, 32(3):118-123
DOI:10.4103/0971-6203.35724  PMID:21157531
A self-shielded medical cyclotron (11 MeV) was commissioned at our center, to produce positron emitters, namely, 18 F, 15 O, 13 N and 11 C for positron emission tomography (PET) imaging. Presently the cyclotron has been exclusively used for the production of 18 F - for 18 F-FDG imaging. The operational parameters which influence the yield of 18 F - production were monitored. The radiation levels in the cyclotron and radiochemistry laboratory were also monitored to assess the radiation safety status in the facility. The target material, 18 O water, is bombarded with proton beam from the cyclotron to produce 18 F - ion that is used for the synthesis of 18 F-FDG. The operational parameters which influence the yield of 18 F - were observed during 292 production runs out of a total of more than 400 runs. The radiation dose levels were also measured in the facility at various locations during cyclotron production runs and in the radiochemistry laboratory during 18 F-FDG syntheses. It was observed that rinsing the target after delivery increased the number of production runs in a given target, as well as resulted in a better correlation between the duration of bombardment and the end of bombardment 18 F - activity with absolutely clean target after being rebuilt. The radiation levels in the cyclotron and radiochemistry laboratory were observed to be well within prescribed limits with safe work practice.
  10,801 649 5
Parameters and computer software for the evaluation of mass attenuation and mass energy-absorption coefficients for body tissues and substitutes
Akintunde A Okunade
July-September 2007, 32(3):124-132
DOI:10.4103/0971-6203.35725  PMID:21157532
The mass attenuation and energy-absorption coefficients (radiation interaction data), which are widely used in the shielding and dosimetry of X-rays used for medical diagnostic and orthovoltage therapeutic procedures, are strongly dependent on the energy of photons, elements and percentage by weight of elements in body tissues and substitutes. Significant disparities exist in the values of percentage by weight of elements reported in literature for body tissues and substitutes for individuals of different ages, genders and states of health. Often, interested parties are in need of these radiation interaction data for body tissues or substitutes with percentage by weight of elements and intermediate energies that are not tabulated in literature. To provide for the use of more precise values of these radiation interaction data, parameters and computer programs, MUA_T and MUEN_T are presented for the computation of mass attenuation and energy-absorption coefficients for body tissues and substitutes of arbitrary percentage-by-weight elemental composition and photon energy ranging between 1 keV (or k-edge) and 400 keV. Results are presented, which show that the values of mass attenuation and energy-absorption coefficients obtained from computer programs are in good agreement with those reported in literature.
  5,378 398 1
Evaluation of partial volume effect correction methods for brain positron emission tomography: Quantification and reproducibility
Merisaari Harri, Teras Mika, Hirvonen Jussi, S Nevalainen Olli, Hietala Jarmo
July-September 2007, 32(3):108-117
DOI:10.4103/0971-6203.35723  PMID:21157530
Quantitative accuracy of positron emission tomography (PET) is decreased by the partial volume effect (PVE). The PVE correction (PVC) methods proposed by Alfano et al., Rousset et al., Müller-Gδrtner et al. and Meltzer et al. were evaluated in the present study to obtain guidelines for selecting among them. For accuracy evaluation, the Hoffman brain phantom was scanned with three PETs of differing spatial resolution in order to measure the effect of PVC on radioactivity distribution. Test-retest data consisting of duplicate dynamic emission recordings of the dopamine D2-receptor ligand [ 11 C] raclopride obtained in eight healthy control subjects were used to test the correction effect in different regions of interest. The PVC method proposed by Alfano et al. gave the best quantification accuracy in the brain gray matter region. When the effect of PVC on reliability was tested with human data, the method of Meltzer et al. proved to be the most reliable. The method by Alfano et al. may be better for group comparison studies and the method by Meltzer et al. for intra-subject drug-effect studies.
  5,304 423 5
EDITORIAL
Evolution of dosimetric quantities of International Commission on Radiological Protection (ICRP): Impact of the forthcoming recommendations
AS Pradhan
July-September 2007, 32(3):89-91
DOI:10.4103/0971-6203.35719  PMID:21157526
  4,515 819 5
ORIGINAL ARTICLES
Dose linearity and uniformity of Siemens ONCOR impression plus linear accelerator designed for step-and-shoot intensity-modulated radiation therapy
Janhavi R Bhangle, VK Sathiya Narayanan, Shrikant A Deshpande
July-September 2007, 32(3):103-107
DOI:10.4103/0971-6203.35722  PMID:21157529
For step-and-shoot type delivery of intensity-modulated radiation therapy (IMRT), beam stability characteristics during the first few monitor units need to be investigated to ensure the planned dose delivery. This paper presents the study done for Siemens ONCOR impression plus linear accelerator before commissioning it for IMRT treatment. The beam stability for 6 and 15 MV in terms of dose monitor linearity, monitor unit stability and beam uniformity is investigated in this work. Monitor unit linearity is studied using FC65G chamber for the range 1-100 MU. The dose per MU is found to be linear for small monitor units down to 1 MU for both 6 and 15 MV beams. The monitor unit linearity is also studied with portal imaging device for the range 1-20 MU for 6 MV beam. The pixel values are within ±1σ confidence level up to 2 MU; for 1 MU, the values are within ±2σ confidence level. The flatness and symmetry analysis is done for both energies in the range of 1-10 MU with Kodak diagnostic films. The flatness and symmetry are found to be within ±3% up to 2 MU for 6 MV and up to 3 MU for 15 MV.
  4,799 367 7
Evaluation methods for detecting changes in beam output and energy in radiation beams from high-energy linear accelerators
R Ravichandran, JP Binukumar, CA Davis, K Krishnamurthy, SS Sivakumar
July-September 2007, 32(3):92-96
DOI:10.4103/0971-6203.35720  PMID:21157527
There is need for simple methods for checking consistency of beam outputs and energy in linear accelerators used for radiotherapy. A method was designed by the department using perspex phantom with which the dosimetric data of two medical linear accelerators (Clinac 600 CD, Clinac 2300 CD) were evaluated over a period of 30 months. The efficacy of methods followed was checked. Routine beam consistency checks were designed for photon beams with 15 cm/ 5 cm depth ionizations in perspex phantom and variable depth combinations for electron beams. Calculated ionization ratios were compared with measured values to show their significance. The dose/MU for all radiation beams was maintained within 2% accuracy over the period of 30 months. Clinac 600 CD machine showed decreasing trend of cGy/MU, while Clinac 2300 CD showed increasing trend of cGy/MU over a period, which needed tuning of monitor chamber two times each. Tuning of output to achieve standard value was carried out once, for all electron energies when the output dose/MU exceeded 3%. During one week (June 2005), there were slight changes in electron energy detected using the ratio method, which did not recur anytime afterwards. The methods designed are adequate to find the consistency in the beam output and energies in the radiotherapy linacs.
  4,140 597 1
BOOK REVIEW
A Ph.D. thesis by S. Brindha entitled 'Investigation of the characteristics of fricke and normoxic polymer gel dosimeters with optical, magnetic resonance and computed tomography readout systems'
Clive Baldock
July-September 2007, 32(3):133-134
  4,180 334 -
NEWS
News
T Ganesh
July-September 2007, 32(3):135-138
DOI:10.4103/0971-6203.35727  
  3,991 182 -
ORIGINAL ARTICLES
Clinical validation of software for a versatile variability analyzer: Assessment of autonomic function
TS Ananthakrishnan, GD Jindal, Vineet Sinha, Rajesh K Jain, SK Kataria, Alaka K Deshpande
July-September 2007, 32(3):97-102
DOI:10.4103/0971-6203.35721  PMID:21157528
Study of physiological variability is an upcoming area of research having manifold clinical applications. Considerable work has been done on heart rate variability and blood pressure variability during the past four decades. Electronics division, Bhabha Atomic Research Centre, has developed an instrument called medical analyzer, which can be used to study several variabilities simultaneously. This instrument has been used to collect data from control subjects and patients with established diagnosis. The data has been analyzed with the help of a software package developed for this purpose and has been found to be consistent with expected manifestations of the disease on the autonomic nervous system. The description of the software package and results of the study are briefly described in this paper.
  3,711 272 2
 
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