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Biomedical subjects

S J Supe

Publications and source records attributed to S J Supe.

At least 19 recordsLinked to original sources
PubMed1995

Many component model and its parameters to fractionated irradiation.

PURPOSE: In this study, a many component model has been formulated to address the contribution of various bio-molecules in radiation induced biological damage and this model is fitted to radiation isoeffect data to evaluate the parameter alpha/beta. MATERIAL AND METHODS: Every living cell contains a number of organic and inorganic molecules which may act as targets to lead radiation induced damage. During irradiation, many kinds of physical, chemical and biological products are produced which are due to active participation of aforesaid molecules. The many component model, hereinafter called linear-quadratic-cubic (LQC) model, is an attempt to provide a better mathematical formulation which could demonstrate the contribution of various kinds of biomolecules in biological effect of radiation. This model has only one independent parameter alpha/beta and a number of dependent parameters which are the derivatives of alpha/beta. RESULTS: Three methods, for testing the fit of the proposed model and deriving the values of alpha/beta, are employed using multifractionation isoeffect data. These methods, i.e. (logDm-logDn) versus (dn-dm) plot, SFe-plot and logD versus d plot, provide their respective values of alpha/beta as 12.50 Gy, 12.51 Gy and 12.54 Gy for spleen. 7.41 Gy, 7.79 Gy and 7.42 Gy for kidney, 15.87 Gy, 15.09 Gy and 14.69 Gy for colon with 3 h interval, 12.50 Gy, 12.84 Gy and 12.45 Gy for colon with 12 h interval and 8.47 Gy, 8.84 Gy and 8.51 Gy for colon with 24 h interval. Since other parameters of the model are the derivatives of alpha/beta therefore can be derived using the values of alpha/beta. DISCUSSION: Graphical representation of afore said sets of data show that the plotted points have a certain amount of scattering which is not at the wider scale and can be well or less well described by a straight line. CONCLUSION: This model eliminates the shortcomings of LQ model and provides a satisfactory explanation of various radiobiological processes occurring during and after irradiation.

Animals↗
PubMed1993

Early skin reactions in head and neck malignancy treated by twice-daily fractionated radiotherapy--estimation of alpha/beta of LQ model.

Conventional radiotherapy, the five times a week regime, fails to achieve locoregional control in a large proportion of advanced carcinomas of head and neck and cervix. Different non-conventional fractionation schedules are being investigated to improve the tumour control rate but, during treatment of advanced malignancy with curative intent, it is seldom possible to deliver a radical dose to the tumour because of the constraint of inducing irreparable normal tissue complications. To compare the probability of occurrence of normal tissue damage and gain in therapeutic ratio various empirical models such as NSD, TDF, CRE and TSD have been suggested, and recently the linear quadratic (LQ) model has been gaining popularity and is claimed to be superior to earlier empirical models. We have studied twice-daily fractionated schedules in head and neck malignancy with the aim of estimating the alpha/beta value of the LQ model for early acute skin effects, and found it to be 9.16 Gy, 7.66 Gy and 8.59 Gy for mild erythema, intensive erythema and dry desquamation respectively.

Carcinoma, Squamous Cell↗
PubMed1993

Alpha/beta value and importance of dose per fraction for the late rectal and recto-sigmoid complications.

A total of 203 patients with cancer of cervix stage IIIB, treated by radiation alone were analysed retrospectively for the incidence of late rectal and recto-sigmoid complications. The patients were treated with a combination of external irradiation and a single intracavitary insertion during January 1979 to December 1983. The external irradiation was randomised to deliver by four different fractionation regimens having dose per fraction of 2 Gy, 3 Gy, 4 Gy and 5.4 Gy. The doses for various fractionation regimens were matched using the time dose factors (TDF) model. 39 cases of late radiation induced rectal and recto-sigmoid complications were observed. The complication rate increased significantly (p < 0.05) with the size of dose per fraction. Using this clinical data an alpha/beta value of 3.87 +/- 0.74 Gy was estimated for late rectal and recto-sigmoid complications.

Adenocarcinoma↗
PubMed1993

Late radiation induced laryngeal oedema in the treatment of vocal cord cancer: analysis using the linear quadratic model.

The incidence of late complications for different size of dose per fraction is analysed in 208 cases with squamous cell carcinoma of the vocal cord. The series comprised 156 cases with T1 and 52 cases with T2 lesions. Radical radiotherapy was given with three different regimens having dose per fraction as 3.33, 2.5 and 2.25 Gy. There were 46 cases with persisting radiation induced laryngeal oedema. Using two different statistical methods, an alpha/beta value of 2.38 Gy of linear quadratic model was estimated for late complications of vocal cord. The analysis indicate the increased incidence of late complications with size of dose per fraction. Relevance of linear quadratic model for the prediction of late complication is demonstrated in the present study.

Carcinoma, Squamous Cell↗
PubMed1993

Linear quadratic model--estimation of alpha/beta ratio for mucosal reaction.

In radiotherapy to ensure that appropriate tumor lethal dose is delivered without exceeding normal tissue tolerance, concepts like NSD and its derivatives were used in the past. Due to their short coming these concepts are now replaced by a linear quadratic model. As this model is based on the recent radiobiological data, it is claimed to be able to predict the biological responses of tumors as well as normal tissues more accurately. However, the accuracy of prediction depends on the precise values of various parameters such as alpha/beta, repair constant mu and repopulation factor that are involved in the linear quadratic model. For most of the tumors and normal tissues, values of the parameters are not yet accurately known. We have estimated alpha/beta value for mucosal reactions, i.e. normal tissue early reactions in head neck cases treated with twice daily fractionation schedules and observed it to be 7.90 Gy for slight mucositis whereas it is 7.68 and 8.11 Gy for patchy and confluent mucositis, respectively.

Carcinoma, Squamous Cell↗
PubMed1993

Dose computation for irregular fields in cobalt-60 beam.

Dose computation in large irregular fields used for treating certain malignant tumors cannot be done by equivalent field methods. The present methods available for such dose computations are accurate but complicated and tedious and are amenable to only computers. This paper describes an algorithm (a semiempirical formula) of dose computation in an irregular field. Attempt is also made to estimate the dose outside the field border and in the shielded region. The dose values computed with this method at different depths in mantle and inverted Y-field in a cobalt-60 beam are compared with the experimentally measured values. The method proves to be simple and accurate. The calculations can be done even manually with a calculator and a statistical table in the absence of computer facility. It also successfully estimates the dose in the shielded region and in the penumbra.

Algorithms↗
PubMed1992

Predictive role of TDF values in late rectal recto-sigmoid complications in irradiation treatment of cervix cancer.

Radiation-induced late rectal and recto-sigmoid complications for different doses per fraction were analyzed retrospectively in 203 cases of Stage IIIB carcinoma of the uterine cervix. The patients were treated with a combination of external irradiation and a single intracavitary insertion during January 1979 to December 1983. The external irradiation was randomised to deliver by four different fractionation regimens having dose per fraction of 2 Gy, 3 Gy, 4 Gy and 5.4 Gy. The doses for various fractionations were matched with the daily regimen using the time-dose factors (TDF) model. A single intracavitary insertion delivered a dose of 22 to 24 Gy to point A using Fletcher-Suit applicator. All patients had a minimum follow-up of 30 months. Thirty nine cases of late radiation induced rectal and recto-sigmoid complications were observed. The complication rate of 8.2% for daily treatment regimen delivering 2 Gy per fraction was increased to 33.3% for once weekly treatment regimen delivering 5.4 Gy per fraction (p = 0.041). Despite similar Time-Dose Factors (TDF) values in four different treatment regimens, the complication rate increased significantly in the once weekly regimen. The analysis suggest that the Time-Dose Factors (TDF) values do not predict correctly the late normal tissue reactions for different dose fractionation schedules.

Adult↗
PubMed1992

The predictive role of bioeffect dose models in radiation-induced late effects in glottic cancers.

Late radiation-induced laryngeal oedema for different doses per fraction was analyzed in 208 cases with squamous cell carcinoma of the vocal cord. The series comprised 156 cases with T1N0M0 and 52 cases with T2N0M0 lesions. Radical radiotherapy was given with three different regimens delivering 3.33 Gy, 2.5 Gy, and 2.25 Gy per fraction. There were 52 cases of late radiation-induced laryngeal oedema. A strong correlation (p less than 0.015) between the dose per fraction and the risk of the late complication in the vocal cord has been demonstrated. The analysis suggests that the empirical models like Nominal Standard Dose (NSD) or Time-Dose Factors (TDF) do not predict correctly the late normal tissue reactions for different dose fractionations. The analysis with extrapolated response dose (ERD) values of the linear-quadratic (L-Q) model also fail to correlate with the late complications (p greater than 0.5). Care should be exercised when using these bioeffect dose models to calculate regimens iso-effective for late damage, even when modest changes in fraction size from 2 to 3 Gy are contemplated.

Carcinoma, Squamous Cell↗
PubMed1991

Treatment of keloids by 90Sr-90Y beta-rays.

The use of radiations for the treatment of keloids was the topic of debate for years. Because of the benign nature of the keloids, surgery (keloidectomy) was treatment of choice. However, the use of surgery alone for arresting the keloids growth does not give satisfactory results due to the high frequency of recurrences. In this study 110 symptomatic cases were treated with 90Sr-90Y beta-radiation either alone for flat keloids or in combination with surgery for thick keloids. The results obtained with this method were found to be quite satisfactory. Patients were given four fractions of 5 Gy per fraction either as weekly or twice weekly schedules. Radiation dose of 2000 cGy given twice weekly in four fractions showed response in 86% of the cases as compared to 73% in those receiving four fractions of 5 Gy weekly. Further observations on different time dose fractionation schedules would open up newer dimensions in the radiotherapy of keloids.

Adolescent↗
PubMed1991

Importance of dose per fraction and estimation of an alpha/beta value for the late complications of the vocal cord.

The incidence of late complications for different sizes of dose per fraction is analysed in 208 cases with squamous cell carcinoma of the vocal cord. The series comprised 156 cases with T1N0M0 and 52 cases with T2N0M0 lesions. Radical radiotherapy was given with three different regimens having dose per fraction of 3.33 Gy, 2.5 Gy and 2.25 Gy. There were 46 cases of late radiation induced laryngeal oedema. Using this clinical data an alpha/beta value of 2.35 +/- 0.13 Gy was estimated for late complications of the vocal cord. It was found that there is strong correlation between size of dose per fraction and the risk of late complication in the vocal cord.

Carcinoma, Squamous Cell↗
PubMed1990

Dose equivalent response of a TLD badge--influence of body backscatter.

In personnel monitoring, operational quantities recommended by ICRU Publication No. 39 for photon radiation can be realized by calibrating dosimeters on a phantom and considering body backscatter photons by using established conversion factors. Personnel dosimeters used in this study are based on CaSO4:Dy Teflon thermoluminescence dosimeter discs (TLD) that have a highly photon energy-dependent response. Since body backscattered photons have lower energies than the incidence photons, methods for correcting for energy dependence of both the incident and body backscattered photons have to be developed. By using readouts of two TLD discs (one under a composite metal filter and the other without a metal filter) in an empirical relation valid at all energies, it is possible to correct for the effect of change in response from change in the photon energies. It was found that the new operational quantities recommended by ICRU could be estimated to within +/- 15% by a TLD badge design based on this method. Angular dependence limits for photons in accordance with the new international standards and a high beta dose-equivalent discrimination in the mixed fields of beta and low-energy x rays could also be achieved.

Equipment Design↗
PubMed1987

Volume correction factor in time dose relationships in brachytherapy.

Paterson's clinical data about the maximum tolerance doses for various volumes of interstitial implants with Ra-226 delivered in seven days was made use of in deriving volume correction factors phi v and phi'v for TDF and CRE concepts respectively for brachytherapy. The derived volume correction factors phi v for TDF and phi'v for CRE differ from the from the one assumed for CRE by Kirk et al. and implied for TDF by Goitein. A normalising volume of 70 cc has been suggested for both CRE and TDF concepts for brachytherapy. A table showing TDFv, the volume corrected TDF, is presented for various volumes and dose rates for continuous irradiation. The use of this table is illustrated with examples.

Brachytherapy↗
PubMed1984

Radiation dose to the breast during mammography: a comprehensive, realistic Monte Carlo calculation.

Certain assumptions have been made regarding the composition of the breast in different age groups: these are believed to be more realistic than existing assumptions and have been used in comprehensive Monte Carlo calculations of radiation dose to the breast and of appropriate indicators of risk as follows: (i) Mean dose to the sensitive tissues in an average breast. This may be used to compare risk in different mammographic techniques, and has been calculated for a wide variety of techniques, including some not previously explicitly studied. (ii) Integral dose to the sensitive tissues in a breast, which is a good indicator of risk in an individual case, has been calculated for two commonly used mammographic techniques and for four different breast compositions and thicknesses. The results have been compared with results obtained using other approaches.

Adolescent↗
PubMed1979

Isoeffect lines using TDF and CRE concepts.

In most of the radiotherapy centres the treatment planning is based on isodose lines. Isoeffect lines are also being drawn based on the concepts of TDFs and CREs. It was aimed in this work to find out whether the isoeffect lines based on the concepts of TDFs, CREs and the physical isodose lines are identical in all the treatment situations. Isoeffect lines for a few treatment schedules involving treatment of carcinoma of the bladder, treatment of cancer of the uterine cervix by combined intracavitary and external beam therapies and intracavitary therapy alone have been obtained and compared in the present study. The effect of treatment mode on the isoeffect lines is also studied. It is found that the isodose curves and the isoeffect lines using the TDF and CRE concepts are not identical in all situations. Therefore, the ultimate treatment plans based on theses isoeffect lines will not be exactly the same. The dependence of the isoeffect lines with the variation of the exponents of time and number of fractions used in the empirical relationship for NSD have also been investigated. Clinical trials have been initiated in the case of cancer of the bladder and cervix uterus based on the isodose curves and the isoeffect lines using CRE and TDF concepts.

Cobalt Radioisotopes↗
PubMed1979

Gap corrections for brachytherapy.

With discrete radiation sources, it is a deliberate treatment policy to provide gaps between two implantations of radioactive sources. Gap correction formulae have been arrived at to evaluate the ultimate biological effect on tissue. These formulae do not maintain the identity of the CRE and TDF concepts and hence Supe and Supe have chosen for external beam treatments appropriate gap corrections which maintain the equivalence of the concepts. During the continuous radiation therapy the tissue cells have a tendency to clump together in the sensitive phase and hence the radiation dose is more effective in this mode of treatment. Consequently the mathematical expressions for the CRE and TDFs for continuous radiation therapy differ from those for external beam therapy. The formula for complex treatment schedules of external beam therapy will not apply to those in brachytherapy, have been arrived at. In order to simplify the evaluation of the effective biological effects Tables for value of (T1+G1/T1)-0.155 and CRE0.71 have been prepared. The formulae developed for the resultant CREs and TDFs for the combination of brachytherapy treatments with gaps are different than those for combinations of external beam therapy. The powers of CRE and the terms of the type (T1+G1/T1) have changed appreciably.

Brachytherapy↗