Journal of Medical Physics
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   1993| April-June  | Volume 18 | Issue 2  
    Online since April 24, 2009

 
 
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Physical Characteristics Of 6 MV And 18 MV Photons From A Dual Energy Linear Accelerator
Anil K Sharma, Sanjay S Supe, K Subbarangaiah
April-June 1993, 18(2):1-5
Clinically pertinent data of the photon beams of nominal energy 6 MV and 18 MV from a dual energy linear accelerator is measured using Radiation Field Analyser with semiconductor diodes and ionisation chambers. Percentage depth dose values are compared with available data from other linacs and BJR-17. Measurements made in the buildup region using parallel plate chamber show a marked increase in the surface dose and dmax shifts by 3 mm and 14 mm for 6 MV and 18 MV photons respectively as the field size is increased from 4 x 4 sq. cm to the maximum. Variations of wedge angles with energy and field size are also determined upto the wedge widths of 15 cm for all the four available wedge angles. lsodose plots for both the energies are obtained using semiconductor diodes in a RFA-3 system. Output factors, wedge transmission factors and shielding tray factors were also measured in clear polystyrene phantom for both the photon energies at the depths of maximum ionisation.
[ABSTRACT]   Full text not available  [PDF]
  805 102 -
Determination Of Exact Point Of Measurement And Surface Dose In An Electron Beam With Cylindrical Ion Chambers
Indra J Das, Harry S Bushe, John F Copeland
April-June 1993, 18(2):16-19
Electron beam dosimetry with a cylindrical ion chamber has had associated with it an uncertainty about the effective point of measurement and difficulty in accurately measuring surface dose. Using two mathematical functions and data taken with a cylindrical ion chamber in air and a phantom, one can determine the effective point of measurement and surface dose for clinical electron beams. We found the effective point of measurement to be inversely related to beam energy. The method detailed here is simple, easy and accurate for the estimation of surface dose in a clinical setting.
[ABSTRACT]   Full text not available  [PDF]
  481 115 -
Role Of Lower Half Body Irradiation (LHBI) In Palliative Treatment Of Disseminated Skeletal Metastases
R.K Vyas, H.A Baboo, P Suresh
April-June 1993, 18(2):23-24
Half body irradiation (HBI) is a new and simple approach for palliative radiotherapy of disseminated skeletal metastasis. It has very good palliative effect with manageable side effects when given as low dose rate treatment. 15 patients with wide spread bony secondaries were treated with Lower half body irradiation (LHBI) at a dose rate of 80-90 c Gy/min at our Institute. Pain relief was observed in all patients. Of these 50% cases had significant relief of pain. Performance status improved and dependence on analgesic drugs had also reduced.
[ABSTRACT]   Full text not available  [PDF]
  525 55 -
Comparative Dosimetry Of Technetium - 99m Labelled Diagnostic Agent In View Of Revised ICRP Recommendations
M.M Gupta, S.C Jain, A Nagaratnam
April-June 1993, 18(2):29-31
Effective dose estimates were made for three renal agents namely Tc-99m - DTPA, Tc-99m - MAG3 and 1-131 - OIH. Biodistribution and mean absorbed dose to various organs / tissues due to Tc-99m - DTPA and 1-131 - OIH were taken from ICRP-53. Similar data for Tc-99m - MAG3 were taken from other published literature. Effective doses due to these agents were computed using earlier as well as the revised values of tissue weighting factors. It is shown that effective dose due to 1-131 - OIH is more than ten times the dose due to Tc-99m labelled renal agents. The revision of tissue weighting factor values results in lowering of the numerical values of effective dose estimates.
[ABSTRACT]   Full text not available  [PDF]
  467 59 -
Pc-At Based Program For Visualization Of Three Dimensional Surfaces
B Singh, Kavita Gupta, B.R Bairi
April-June 1993, 18(2):35-38
A computer program for visualization of three dimensional surfaces is described. The surface is generated from a set of two dimensional slices of a three dimensional object. A three dimensional binary object is generated by selecting a suitable gray level window. The cubic voxel approach has been used for description of the object. The boundary surface is tracked from the user specified starting point. The options for specification of spin and tilt angles lead to visualization of the other side of the object. Surface shading is carried out based on the direction of the surface normals. The two dimensional gray level image is then displayed on the computer terminal.
[ABSTRACT]   Full text not available  [PDF]
  475 49 -
A Fast Response Wide Range Solid State Densitometer
H.K Pendurkar, U.P Gaonkar, A.T Soman, R.N Das Sarma
April-June 1993, 18(2):32-34
Routine assessment of radiation doses for about 18,000 persons per month is still being carried out by the Radiation Protection Services Division through its Film Badge Service, in addition to 21,000 per month through TLD. This necessitated, earlier, the development of a semiautomatic Film Densitometer Reader which uses a densitometer having an expensive photomultiplier with associated high voltage supply and elaborate electronic circuitry covering a linear range of 0-4 optical density. This paper describes a linear densitometer developed using an ultrasensitive fast response silicon photodiode (which forms part of a solid state photo detector - amplifier combination) and a temperature compensated log ratio amplifier. The instrument is simple, cost-effective and reliable. It measures diffuse optical density of the monitor film in the range of 0 to 5 with a least measurable density of 0.01.
[ABSTRACT]   Full text not available  [PDF]
  447 73 -
Calculation Of Biological Dose For Treatment Of Carcinoma Of Esophagus Using External Irradiation And High Dose Rate Intraluminal Irradiation
Ranjan K Sur, Pritam S Negi, Deepinder P Singh, Suresh C Sharma, Brahm D Gupta
April-June 1993, 18(2):20-22
A combination of moderate doses of external beam irradiation and intraluminal irradiation has been found to give the best results in esophageal cancer. In advanced cases, with massive local disease the purpose of moderate doses of external beam irradiation is to shrink the local tumour so that intraluminal irradiation is possible in 2-3 weeks. We give 35 Gy / 15 fractions in 3 weeks by external beam and 12 Gy calculated at 1.0 cm from the centre of the source axis in two sessions of 6 Gy each, a week apart by HDR intraluminal irradiation. In this report, the various formulae necessary to calculate the effective biological dose by CRE. TDF and LQ models have been outlined when the combined modality is used for therapy.
[ABSTRACT]   Full text not available  [PDF]
  409 80 -
Geometrical Reconstruction And Manual Dosimetry Of Interstitial Iridium Implants
R.M Nehru, J.S Avadhani, S.M Deore, P.S Viswanathan, K.A Dinshaw
April-June 1993, 18(2):6-10
The dosimetric calculations in several planes using treatment planning systems give a clear perception of dose distribution of the implant. It is impractical to do the complete dosimetry where the facility 'of treatment planning system is not available or in case of failure. of such system. Taking this into consideration a method of reconstruction of geometry of implant using orthogonal films and manual method of dosimetry are described based on Paris System. Initially a double plane implant geometry was constructed in a phantom and sets of orthogonal films were taken by orienting the phantom at different angles in order to simulate possible implant geometry inside the patient. Using the set of orthogonal X-rays the X and Z coordinates were obtained. The plot of X versus Z will give the reconstructed geometry of the implant. This was found to match fairly with the transverse section taken from CT scan. Later the method was also confirmed with actual clinical implants.
[ABSTRACT]   Full text not available  [PDF]
  414 47 -
Performance Assessment Of The Barc Activity Meter
Raghu Ram K. Nair
April-June 1993, 18(2):11-15
The performance of the activity meter Model NIS / ED-27, designed by the Electronics Division, BARC was evaluated at the time of acceptance and in the hospital, periodically. Parameters like Precision, Accuracy, Linearity, the effect of sample position, sample volume and Background were assessed. Certain modifications are suggested for making the instrument universally acceptable.
[ABSTRACT]   Full text not available  [PDF]
  377 50 -
Radiosurgery For Arteriovenous Malformations Based On Magnetic Resonance Angiography
Minesh Mehta, Shrikant Kubsad, Daniel Petereit, Patrick Turski, Allan Levin, Timothy Kinsella
April-June 1993, 18(2):25-28
Full text not available  [PDF]
  277 41 -
 
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