Journal of Medical Physics
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   1997| October-December  | Volume 22 | Issue 4  
    Online since April 23, 2009

 
 
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Surface Dose Measurements Using Parallel Plate Markus Chamber For 60co, 6 & 10 MV Photon Beams
HK Malhotra, DD Deshpande, SV Salvi
October-December 1997, 22(4):169-194
Fixed volume parallel plate ion chambers are commonly employed for surface dose measurement purposes as the much desired extrapolation chambers are rarely available in a department. They, however, overestimate the surface doses by an appreciable amount, sometimes as much as a factor of 2, and needs careful consideration before using measured data for clinical dosimetry. Surface dose measurements were carried out for 60Co, 6 and 10 MV photon beams using a PTW Markus parallel plate chamber as well as UF TLD powder. The Markus chamber was found to over-response the surface dose measurements by 18.7%, 10.6% and 6.7% in absolute terms for 6 0co, 6 and 10 MV, respectively, which is in conformity with the available literature.
[ABSTRACT]   Full text not available  [PDF]
  742 173 -
Depth Dose Study Of A High Activity Ir-192 Source Using Computer Controlled 3-Dimensional Data Acquisition System
RM Nehru, AS Pradhan, A Sankar, DD Deshpande
October-December 1997, 22(4):165-168
The aim of the present study was to carry out the physical measurements such as depth dose around a high activity lr-192 source and derive the radial dose factors and compare with the published data. A commercial computer controlled 3-D water phantom system (WPS) was used with an ion chamber of 0.125 cc (PTW, Freiburg, Germany). The chamber was 1 cm long and 0.55 cm diameter and enclosed in a 100 cm long rubber tube. The chamber was connected to an electrometer and operated at a voltage of 300 V. The ionization measurements were made along the perpendicular bisector of the source at a regular interval. Depth dose curve was obtained and radial dose factors were derived. This study improves our confidence in measurement using 3-dimensional WPS and the small size detectors coupled with the electrometer. The present radial dose factors, g(r) values, may be used in clinical situations where secondary dose at other parts of the body located at larger distances are warranted.
[ABSTRACT]   Full text not available  [PDF]
  480 61 -
Evaluation Of Transit Times By Deconvolution Analysis In A Radionuclide Renogram
HK Rajabi, GS Pant
October-December 1997, 22(4):178-181
A programme using matrix algorithm for deconvolution analysis of renogram has been developed at our centre in a (Siemens) microdelta computer (Siemens Ltd) in Fortran based Medical language. A total of sequential trames are acquired with both the kidneys facing the detector. The desired kidney regions are selected for deconvolution analysis. The software plots the retention function for each region of the kidney and computes minimum transit time (MinTT), mean transit time (MTT), transit time index (TTI) and maximum transit time (MaxTT) for them. Any prolongation of the transit time of the radioactive tracer through the different regions of the kidney becomes an important and reliable diagnositic tool for upper urinary tract obstruction.
[ABSTRACT]   Full text not available  [PDF]
  447 57 -
Application Of ERD To Complied Data On Spinal Cord Myelitis Arriving At Tolerance ERD Value
J Velmurgan, SS Supe, GNS Prasad, JGR Solomon, Koteshwer Rao
October-December 1997, 22(4):175-177
The spinal cord, because of its anatomical location, is at risk in large number of radiotherapy treatments. Treatment techniques designed to minimize risk of spinal cord injury, are likely to underdose the tumor, with consequent failure to control the disease. Since radiation myelopathy results in severe and irreversible morbidity, it is important to establish the tolerance dose to the spinal cord. Many clinical studies indicate a dose of 45 Gy in 22 to 25 fractions in 30 to 35 days as the tolerance dose which is on the conservative side, from the point of view of tumor control probability. Deciding spinal cord tolerance on the basis of Extrapolated Response Dose (ERD) would be a better approach. This study was designed to evaluate the effects of prognostic factor ERD on the probability of myelitis, for a compiled retrospective clinical literature data. Patients were classified on the basis of ERD and were statistically correlated with the incidence of myelitis. An ERD limit of 130 Gy appears to be the tolerance bioeffect dose for acceptable level of probability of spinal cord myelitis while designing inovative fractionation schemes in clinical radiotherapy.
[ABSTRACT]   Full text not available  [PDF]
  360 59 -
World Congress On Medical Physics And Biomedical Engineering,
P.S. Iyer
October-December 1997, 22(4):182-182
Full text not available  [PDF]
  330 80 -
 
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