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P S Nagarajan

Publications and source records attributed to P S Nagarajan.

15 recordsLinked to original sources
PubMed2006

Normalized organ doses and effective doses to a reference Indian adult male in conventional medical diagnostic x-ray examinations.

This work discusses the dose computations of 80 kV diagnostic x-rays made on a mathematical phantom representing an average Indian adult, since it is felt that results based on MIRD adult phantom calculations are not strictly appropriate for the population in India. Normalized organ equivalent doses and effective doses for an Indian adult male have been estimated. Normalization is done with respect to the entrance skin dose of the patient. Twenty common diagnostic x-ray examinations have been considered in this study and the doses are presented. This study would enable estimation of radiation induced detriment to the patient subpopulation in India. Since the external dimensions of the phantom are nearly the same as that of 15-y-old NRPB pediatric phantom, our results are also compared with those of latter and the agreement was found to be satisfactory.

Adolescent↗
PubMed2003

A semi-analytic approach to determine dose rate constant of brachytherapy sources in compliance with AAPM TG 60 formalism.

Values of dose rate constant (DRC) in compliance with AAPM TG 60 formalism recommended for intravascular brachytherapy (IVBT) were calculated for different point isotropic mono-energetic photon sources in the energy range E = 20-1000 keV using a semi-analytic model. Based on these DRC values, DRC of some existing models of 192Ir and 125I brachytherapy sources were then calculated using (1) bare energy spectra and (2) a single energy parameter which represents mean energy (photon number weighted or air-kerma weighted) for bare and actual sources or the most probable energy of the spectra (energy line with the highest probability of emission) of the investigated sources (192Ir and 125I). Applicability of the semi-analytic approach was examined by also computing the values of DRC of the investigated sources using MCNP Monte Carlo simulation code (Version 3.1) that involved modeling of the sources accurately. A comparison of values of DRC resulting from MCNP calculations with those resulting from the semi-analytic approach showed that for 192Ir sources the agreement was within 0.40% and for 125I sources it was within 2.3%.

Brachytherapy↗
PubMed2002

Room scatter studies in the air kerma strength standardization of the Amersham CDCS-J-type 137Cs source: a Monte Carlo study.

Corrections for room scatter, [kSC (d, H)]RM, as a function of source-to-detector distance, d, and source-to-floor-height, H, and also departure from constant room scatter. ks1, have been computed for rooms of various sizes using Monte Carlo methods for air kerma strength standardization of the Amersham CDCS-J-type 137Cs brachytherapy source. These corrections will also be applicable to any type of 137Cs source that may be considered for standardization. It was found that, depending upon the relative position of the source with respect to the surrounding concrete scattering surfaces (side walls, floor and ceiling) and different set of d values, the assumption of constant room scatter overestimated the air kerma strength, Sk, by between 0.2% and 0.6%.

Air↗
PubMed2001

Monte Carlo aided room scatter studies in the primary air kerma strength standardization of a remote afterloading 192Ir HDR source.

Corrections for room scatter, [ksc(d, H)]RM, were derived using Monte Carlo methods for rooms of various sizes, including the brachytherapy treatment room, in which primary air kerma strength standardization of a remote afterloading microSelectron 192Ir HDR source was carried out, using a 60 cm3 spherical graphite ion chamber. It was observed that for a given source-to-floor height, H, the air kerma rate due to room scatter was found to be decreasing with increase in source-to-detector distance, d, whereas it is assumed to be constant in the experimental determination (multiple-distance method) of the air kerma strength (AKS). Irrespective of the room size considered in the present study and when H = 100 cm, the assumption of 'constant room scatter' for d = 50, 75 and 100 cm resulted in overestimation of the AKS by about 1%. However, when d was in the range 13-25 cm, it was only 0.20%. The room scatter correction for the shadow cone method was also computed and the result showed that no additional correction was required on account of forward scatter from the cone. Further, at larger d (50-100 cm), the number of low-energy photons (40-200keV) relative to the total number of photons was found to be very significant, which may be useful to revisit the Spencer-Attix cavity theory.

Air↗
PubMed1979

Computed LET distributions in the build-up region of tissue for 14 MeV neutrons.

Experimental radiobiological investigations of fast neutron beams involve irradiation of thin cell layers. The irradiation of cells is done either in free air or with a material such as graphite, TE plastic or bone-equivalent plastic covering the cells. This paper discusses the computed dose distributions in LET at shallow depths between 5 or 10 micrometers and the equilibrium depth, and the influence of the overlying materials on the distributions. The secondaries considered are elastic recoils of H, C, N and O, and 22 alpha particle groups and the corresponding heavy recoils arising from (n, alpha) events in C, N, O, P and Ca. Dose-average LET and curves of detailed dose distributions in LET as a function of depth in tissue are given for various overlying materials.

Energy Transfer↗