Biomedical subjects

A S Pradhan

Publications and source records attributed to A S Pradhan.

At least 19 recordsLinked to original sources

PubMed2006

Development of an algorithm for TLD badge system for dosimetry in the field of X and gamma radiation in terms of Hp(10).

In view of the introduction of International Commission on Radiation Units and Measurements operational quantities Hp(10) and Hp(0.07), defined for individual monitoring, it became necessary to develop an algorithm that gives direct response of the dosemeter in terms of the operational quantities. Hence, for this purpose and also to improve the accuracy in dose estimation especially in the mixed fields of X ray and gamma, an algorithm was developed based on higher-order polynomial fit of the data points generated from the dose-response of discs under different filter regions of the present TL dosemeter system for known delivered doses. Study on the response of the BARC TL dosemeter system based on CaSO(4):Dy Teflon thermoluminescence dosemeter discs in the mixed fields of X and gamma radiation was carried out to ensure that the accuracies are within the prescribed limits recommended by the international organisations. The prevalent algorithm, based on the ratios of the disc response under various filters regions of the dosemeter to pure photons, was tested for different proportion of two radiations in case of mixed field dosimetry. It was found that the accuracy for few fields is beyond the acceptable limit in case of prevalent algorithm. The new proposed algorithm was also tested in mixed fields of photon fields and to pure photon fields of varied angles. It was found that the response of the dosemeter in mixed fields of photons and its angular response are satisfactory. The new algorithm can be used to record and report the personal dose in terms of Hp(10) as per the international recommendation for the present TL dosemeter.

Algorithms↗

PubMed2006

Glow peak temperature, supralinearity and LET dependence of TLDs--correlation studies.

The study of the well separated low and high temperature glow peaks in CaSO4:Dy and CaF2:Tm was undertaken to develop comparative data on supralinearity of low and high temperature glow peaks for their use in the estimation of elapsed time of exposure and to analyse their responses to low and high-linear energy transfer (LET) radiation. In CaSO4:Dy, unlike its dosimetric peak, the structure of glow peaks at approximately 140 and 400 degrees C remains unchanged (peak position changes within 4 degrees C) with 60Co gamma-ray exposure up to 1 kGy air kerma. The glow peaks at 140 degrees C exhibited higher supralinearity than that of the peaks at 240 and 400 degrees C. In CaF2:Tm, 110 degrees C glow peak exhibited higher supralinearity and higher response to high-LET radiation as compared with 150 degrees C glow peak. No correlation between glow peak temperature and supralinearity or the LET response was observed.

Calcium Fluoride↗

PubMed2006

Correlation of phase transition with the change in TL characteristics in CaSO4:Dy phosphor--effect of thermal treatment.

The study is aimed at optimising the glow curve structure of CaSO4:Dy phosphor for dosimetric purpose and also to understand the observed changes owing to thermal treatment in the thermoluminescence (TL) sensitivity and glow curve structure. The reversible changes in the intensities of the lower temperature satellite peak and the main dosimetric glow peak with temperature of thermal treatment in the temperature range 400-700 degrees C indicates the interconversion of defect complexes responsible for the glow peaks in CaSO4:Dy. Phosphor samples subjected to thermal treatment in temperature range beyond 800 degrees C, showed irreversible changes in the intensities of the lower temperature and dosimetric peaks. The changes in TL characteristics of the phosphor for thermal treatments >800 degrees C are attributed to the partial phase transition in the phosphor as confirmed by the XRD and TG/DTA analysis of the phosphor.

Calcium Sulfate↗

PubMed2006

Comparison of observed skeleton retention of strontium in average indian adult with the value predicted by the ICRP biokinetic model.

The daily dietary intake of strontium and its content in skeleton, for an Indian adult population group were estimated by experimentally measuring its concentration in total cooked diet and autopsy skeleton samples using radiochemical neutron activation analysis. The data on daily dietary intake of strontium were used to compute its contents in skeleton using ICRP Publication 67 biokinetic model for strontium. The theoretically computed value of strontium (213.8 mg) compared favourably with the measured values (GM 181.2 mg) in an urban population group living in Mumbai representing an average Indian adult (Reference Indian Man).

Adult↗

PubMed2004

Comparison of observed lung retention and urinary excretion of thorium workers and members of the public in India with the values predicted by the ICRP biokinetic model.

The daily intake of natural Th and its contents in lungs, skeleton and liver of an Indian adult population group were estimated using radiochemical neutron activation analysis (RNAA) technique. These data on daily intake (through inhalation and ingestion) were used to compute Th contents in lungs and other systemic organs such as skeleton and liver using the new human respiratory tract model (HRTM) and the new biokinetic model of Th. The theoretically computed Th contents in lungs, skeleton and liver of an average Indian adult are 2.56, 4.00 and 0.17 microg, respectively which are comparable with the corresponding experimentally measured values of 4.31, 3.45 and 0.14 microg in an urban population group living in Mumbai. The measured lung contents of Th in a group of five occupational workers were used to compute their total body Th contents and the corresponding daily urinary excretions. The computed total body contents and daily urinary excretions of Th in the five subjects compared favourably with their measured values. These studies, thus, validate the new biokinetic model of Th in natural as well as in occupational exposures in Indian conditions.

Adolescent↗

PubMed2003

Batch-to-batch variation in the TL glow peaks and sensitivity in the production of CaSO4:Dy TLD phosphor.

The thermoluminescence (TL) glow peak height ratio of the main dosimetric peak (at about 240 degrees C) and the lower temperature satellite peak (at about 140 degrees C) of CaSO4:Dy was found to vary between 1.4 and 11.5 in more than 100 batches of CaSO4:Dy TLD tested in the last 5 years. Efforts were made to minimise the batch-to-batch variation. In most of the batches (90% of cases), the peak height ratio was more than 5 and the variation in the TL sensitivity (with respect to the reference batch) rarely exceeded 10%. The study of the grain size dependence of the peak height ratio of ground and unground and with and without acid wash of phosphor grains indicated that the surface effects contribute significantly to the batch-to-batch variation. Crystallisation of phosphor grains was found to be affected considerably by the interruptions in the process of evaporation of acid during the preparation. Phosphor grain size was found to be an important parameter for maintaining the quality of production of CaSO4:Dy TLD phosphor.

Calcium Sulfate↗

PubMed2002

Effect of heating rate on the responses of CaF2:Cu, CaF2:Tm, CaF2:Dy and CaF2:Mn.

Recent development of CaF2:Cu (the most sensitive material for radiation dosimetry) exhibiting a TL glow peak around 270 degrees C similar to that of CaF2:Mn has made it attractive to study the influence of heating rate on the response of CaF2 based TLDs. Influence of heating rate on CaF2:Mn (known to reduce the response with increasing heating rate) was confirmed in view of the reported controversy about other TLDs. Responses of TL glow peaks around 270 degrees C in CaF2:Cu, CaF2:Tm, CaF2:Dy and CaF2:Mn were studied. Except CaF2:Mn, no other CaF2 based TLD exhibited a reduction in response with increasing heating rate. On the contrary, in some cases a small increase (10-15%) was noted with increasing heating rate from 1 degrees Cs(-1) to 50 degrees Cs(-1). The shape and the position of the glow peak and the parameters derived from the shape of the glow curve appear to have no relation to reduction of TL efficiency at higher heating rates. Apart from the increased probability of non-radiative transitions at higher temperatures, the observed effects have been assigned to the effect of heating rate on the migration of charge carriers released during the TL readout.

Calcium Fluoride↗

PubMed2002

New parameters of annealing and re-use of TLDs based on CaSO4:Dy phosphor.

A study on CaSO4:Dy TLDs was undertaken to confirm the validity of the annealing treatment (400 degrees C, 1 h) for its re-use. The temperature range of the study was from 230 degrees C to 700 degrees C. The effect of thermal treatments on the TL sensitivity and glow curve structure showed that the lattice of CaSO4:Dy is sensitive to thermal treatment in the temperature range from 350 degrees C to 425 degrees C. It is also seen that both TL sensitivity and peak height ratio (dosimetric peak at 240 degrees C to low temperature satellite peak at 140 degrees C) reduces with an increasing number of annealing cycles in the temperature range from 350 degrees C to 425 degrees C. No significant change was observed in TL emission and ESR spectrum of the phosphor. The study shows that the annealing treatment in the temperature range from 600 degrees C to 650 degrees C could be the best alternative for annealing and re-use of CaSO4:Dy phosphor or a temperature below 350 degrees C for Teflon embedded dosemeters.

Calcium Sulfate↗

PubMed2002

Photon energy response of luminescence dosemeters and its impact on assessment of Hp(10) and Hp(0.07) in mixed fields of varying energies of photons and beta radiation.

X and gamma rays continue to remain the main contributors to the dose to humans. As these photons of varying energies are encountered in various applications, the study of photon energy response of a dosemeter is an important aspect to ensure the accuracy in dose measurement. Responses of dosemeters have to be experimentally established because for luminescence dosemeters, they depend not only on the effective atomic number (ratio of mass energy absorption coefficients of dosemeter and tissue) of the detector, but also considerably on the luminescence efficiency and the material surrounding the dosemeters. Metal filters are generally used for the compensation of energy dependence below 200 keV and/or to provide photon energy discrimination. It is noted that the contribution to Hp(0.07) could be measured more accurately than Hp(10). For the dosemeters exhibiting high photon energy-dependent response, estimation of the beta component of Hp(0.07) becomes very difficult in the mixed field of beta radiation and photons of energy less than 100 keV. Recent studies have shown that the thickness and the atomic number of metal filters not only affect the response below 200 keV but also cause a significant over-response for high energy (>6 MeV) photons often encountered in the environments of pressurised heavy water reactors and accelerators.

Beta Particles↗

PubMed2002

Calibration of TLD badges for photons of energy above 6 MeV and dosimetric intricacies in high energy gamma ray fields encountered in nuclear power plants.

CaSO4:Dy and LiF TLDs do not exhibit photon energy dependence beyond +/-55% for photons in the energy range from 1 MeV to about 7 MeV. However, when sandwiched between metal filters or used in TLD badge holders having metal filters, the response changes for irradiation from high energy photons as compared to that from 60Co gamma rays (generally used for reference calibrations). This effect is about the same for both the lower atomic number TLD (LiF) and higher atomic number TLD (CaSO4:Dy). For TLDs held on the surface of the phantom and irradiated in collimated photon beams, the response of TLDs without any filter or those under the open window of the TLD badge is considerably reduced due to insufficient build-up to high energy photons, whereas for uncollimated radiation fields from power reactors, an over-response is observed. It is observed that the use of inappropriate encapsulation of dosemeters would cause a significant error not only in the estimation of doses due to penetrating radiations but also in the estimation of beta doses in the mixed fields of beta radiation, high energy gamma rays and high energy electrons often encountered in the fields of pressurised heavy water reactors.

Calcium Sulfate↗

PubMed2002

The use of computerised glow curve analysis will optimise personal thermoluminescence dosimetry measurements. Opposing the proposition.

Referring to the proposition for this debate, it is necessary to consider what is meant by 'optimise personal thermoluminescence dosimetry measurements'. Much research has been performed on the thermoluminescence glow curves that can be used to determine absorbed dose, and much of the knowledge gained from this research has been put into practice. Thermoluminescence dosemeters are capable of measuring an extremely wide range of doses and dose rates. Nearly all types of radiation can be measured, and some TL dosemeters have been designed to function as elementary spectrometers. More recently, the microdosimetric properties of TL dosemeters have been investigated. TL dosemeters are worn by a large proportion of radiation workers worldwide. But, can we conclude that thermoluminescence dosimetry measurements are at an optimum level? Perhaps that is not a fair question because it may be impossible to say when anything is truly optimum. Although the techniques pointed out by our debaters may not yet be used by all large, personal dosimetry services, as with many recent innovations, implementation may be as near as the next computer chip upgrade.

Algorithms↗

PubMed2000

Process indicators for safe motherhood programmes: their application and implications as derived from hospital data in Nepal.

Measuring maternal mortality ratios is fraught with problems and underestimates. Therefore process indicators have been proposed for monitoring the availability and use of obstetrics services. We report the results of process indicators for measuring the availability, use and quality of obstetric care in five districts in Nepal between 1997 and 1998. The number of comprehensive essential obstetric care (EOC) facilities was adequate for four of the five districts, but none had a minimum acceptable level of basic EOC facilities as set by UNICEF et al. The proportion of expected births in hospital was 21.5% in Rupandehi and < 5% in Baglung, Kailali, Okhaldunga and Surkhet. The minimum acceptable level is 15%. The 'met need' for obstetric care which pertains to the proportion of all women with direct obstetric complications that are treated in hospital was 14.9% in Rupandehi and < 5% in the other four districts, against the required minimum of 15%. The caesarean section rate calculated of all expected births in the population varied between 0.2% and 1.4%. The case fatality rate was 4.0% in Rupandehi Zonal Hospital. Analysis of these indicators clearly identified tremendous underuse of maternity services which has stimulated national policy discussions in Nepal with ensuing safe motherhood interventions and monitoring strategies.

Adult↗

PubMed2000

In-phantom response of LiF TLD-100 for dosimetry of 192Ir HDR source.

An experiment was carried out to reevaluate the response of LiF TLD-100 rods (1 mmx1 mmx6 mm) at different depths in a water substituting phantom to provide an answer to a prevailing controversy about the over-response of LiF to the softened photon spectra of 192Ir HDR source at depths in phantom due to its photon energy dependence. Claims of some authors that LiF TLDs over-responds by 8.5% at 10 cm depth in phantom, necessitating depth-dependent correction factors even for an 192Ir source and of some others for no over-response were evaluated. The over-response of LiF TLD-100 rods, against a calibrated ion chamber having a photon energy-independent response within 2%, was found to be not exceeding 2.5% at a depth of 10 cm in the phantom as compared to a depth at 1 cm, for a precision of the order of +/- 1% (1sigma) in the TLD measurements. By using ISO equivalent photon beams, photon energy dependence of the dosimeters was evaluated and for LiF TLD-100 rods it was found to be in close agreement (within 3%) with the ratios of mass energy absorption coefficients of LiF and water in the range of effective photon energy from 26 keV to 1.25 MeV. Parameters that could contribute to the discrepancy in the reported values of experimental results have been discussed.

Biophysical Phenomena↗

PubMed1997

Dosimetric aspects of physical and dynamic wedge of Clinac 2100C linear accelerator.

AIM: To investigate variation of wedge factors on field size and depth for physical and dynamic wedges of identical wedge angles for Clinac 2100C linear accelerator and its clinical implementation. MATERIAL AND METHODS: A computer controlled water phantom dosimetric system is used to generate profile data for physical wedges, whereas a 0.6 cm3 ion chamber is used for generation of profiles for dynamic wedge and wedge factors for both types of wedges. The method has been discussed to handle the dynamic wedge dosimetry in absence of linear array of detectors or film densitometer. RESULTS: A systematic dependence on wedge factor is observed for physical wedge, with respect to depth and wedge angle but not depending on field size. Whereas dynamic wedge shows strong dependence on field size and is not systematic because the dynamic wedge is controlled by segmented treatment tables depending on field size and energy and no significant variation is observed on depth for various wedge angles. The handling of beam data in a commercially available treatment planning system is discussed and a comparison has been made for iso-doses of both types of wedges. CONCLUSION: The dynamic wedge isodose curves shows rather straight lines than physical wedge but larger hot spots at thin edge which needs careful consideration during planning.

Humans↗

PubMed1997

Dosimetry of intracavitary applications in carcinoma of the cervix: rectal dose analysis.

The International Commission on Radiation Units and Measurements (ICRU), in its Report-38, has given certain recommendations regarding the specifications of bladder and rectal reference points in the intracavitary treatment of carcinoma of the cervix. Conforming to this report, 182 intracavitary applications performed in stage I and II cervix cases were analyzed. In 113 applications, the maximum rectal dose was found to be in a point on the anteroposterior line drawn through the centre of colpostat sources. However, for our type of applications, the point on the anteroposterior line drawn through the lower end of the uterine tube seldom gets maximum dose. In addition, it was observed that there are other dose points than the ICRU reference point receiving doses close to maximum dose. It was concluded that doses to multiple rectal reference points should be recorded, in addition to the ICRU-defined rectal reference point.

Brachytherapy↗

PubMed1996

Geometrical considerations in dose volume analysis in intracavitary treatment.

PURPOSE: The present work was aimed at to study the relationship between the volume enclosed by reference isodose surface and various geometrical parameters of the intracavitary applicator in treatment of carcinoma of cervix. MATERIAL AND METHODS: Pearshape volume of the reference isodose derived from the Total Reference Air Kerma (TRAK) and the product of its dimensions, height H, width W and thickness T which is dependent on the applicator geometry, were estimated for 100 intracavitary applications treated by Selectron LDR machine. Orthogonal radiographs taken for each patient were used for measurement of actual geometric dimensions of the applicator and carrying out the dosimetry on TP-11 treatment planning system. The dimensions H, W and T of reference isodose surface (60 Gy) were also noted. RESULTS: Ratio of the product HWT and the pearshape volume was found mainly to be a function of colpostat separation and not of other geometrical parameters like maximum vertical and anterio-posterior dimension of the applicator. The ratio remained almost constant for a particular combination of uterine tandem and colpostat. Variation in the ratios were attributed to the non-standard geometry. CONCLUSION: The ratio of the volume of reference isodose surface to the product of its dimensions in the applicator depends upon the colpostat separation.

Brachytherapy↗

PubMed1996

The dependency of wedge factors on field size and depth in megavoltage beams.

AIM: To investigate the variation of wedge factors on field size, depth on 2 types of telecobalt units and 3 types of medical linear accelerators and to make a simplified approach for day to day calculation procedure. MATERIALS AND METHODS: A 0.125 cm3 ion chamber was used to determine the wedge factors which is connected to the computer controlled radiation field analyser. The wedge factors were determined for field sizes varying from 5 x 5 cm to the maximum square field size available for each wedge angles and at multiple depths upto 25 cm of respective teletherapy units. The results obtained are fitted to a second degree polynomial function. RESULTS: There is no significant variation of wedge factor on field size for all the 3 linear accelerators. The wedge factors are found to vary mainly at larger depths and wedge angles. The variation of wedge factors for 2 types of cobalt units were similar and increase of 3%, 4% and 5.5% is observed for wedge angles 30 degrees, 45 degrees and 60 degrees respectively with respect of depth of maximum build-up. The trend was similar for linear accelerators with maximum increase in wedge factor up to 7.5% for 60 degrees wedge angle at 25 cm depth for 6 MV photon beams. DISCUSSION AND CONCLUSIONS: The determination of wedge factors at various field sizes and depths is essential to ensure accurate dose delivery. With experimental wedge data fitted with second degree polynomial function is a simplified and alternative method which can be adopted for routine dosimetric calculations.

Cobalt Radioisotopes↗

PubMed1996

Design and comparison of wedge shaped midline block with rectangular block used in early stage cervical cancers.

PURPOSE: Design of an universal wedge shaped midline block for early stage cervical cancers to get uniform dose distribution around the target volume. MATERIAL AND METHODS: The method of fabrication of wedge shaped midline block is discussed for treatment of early stage cervical cancers based on the configuration of 137Cs pellets used in intracavitary applications and along with external photon beams obtained by using 60Co teletherapy machine and 6 and 10 MV linear accelerators. RESULTS: The dosimetric measurements are carried out to confirm the adequacy of thickness and shape of the block using radiation field analyzer for all the 3 energies. DISCUSSION: The dose distribution comparison has been made with wedge shaped midline block and conventional rectangular shields to show its superiority in getting homogeneous dose distribution around target volume. The shift in 184 intracavitary applications is analyzed in actual clinical applications with respect to central axis of external beams and its comparison is made with both types of blocks. With the shift of 1 cm towards lateral from midline an overdose can occur upto 12 Gy at certain points with rectangular block compared to wedge shaped midline block. CONCLUSION: Since the preparation of individual wedge shaped midline block for every application will be a difficult process for busy centers, the single wedge shaped midline block for each energy is more convenient to handle for busy centers instead of individualized compensating blocks for every intracavitary application.

Brachytherapy↗