Precise knowledge of photon beam characteristics in the build-u region is essential for accurate dose delivery in a clinical set up. In the current study, build-up characteristics of 60Co, 6 and 10 MV photon beams have been determined, using a PTW-Markus chamber in a polystyrene phantom. The variation of dmax with increase in field-size is also investigated. . For 60Co, the decrease in dmax with field-size was maximum (60%decrease in dmax when the field-size increases from 5 x 5 to 35 x 35 cm), which may compromise skin sparing at larger field-sizes. All the three photon beams were found to have comparable build-up curves when plotted against d / dmax (%). Errors exceeding 5% were observed in the dose ionisation build-up curve, particularly at shallow depths for 6 and 10 MV photons. Beyond 2 mm depth for 60Co and 5 mm for 6 and 10 MV photon beams, the over-response of the Markus chamber against extrapolation chamber reduceds to less than 2.5%.

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Chemobyl Atomic Power Plant accident is one of the world's most tragic nuclear accidents. It has caused widespread concern because of its radiological consequences. At the same time, it offers an opportunity to learn new lessons. The scientific and technical investigations carried out in the aftermath of the accident are many and encompass an array of complex topics. As the accident's long shadows recede and myths unravel, perspectives sharpen. More light is being shed on the accident's true effects. This review article attempts to collect the results of various studies and present them in an easily comprehensible and succinct manner. Perhaps the pediatric thyroid cancer is the only effect of the disaster established so far beyond doubt.

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This note deals with a computer programme written to cover the recommended teletherapy time calculation procedures used in different techniques of irradiation. The memory required is considerably reduced by proper grouping of common procedures involved in various techniques. For the use of the readers, the programme is presented as flowcharts and explained in detail.

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Status of quality assurance of radiodiagnostic facilities available in certain districts of Tamilnadu and adjoining areas was studied. This study included an exhaustive survey of radiodiagnostic facilities available in the area of interest and several levels of interaction with personnel handling those facilities. It was found that status of quality assurance prevailing in larger hospitals in urban areas were by and large satisfactory, whereas in the case of small hospitals doing grass-root level work, quality assurance was not thought about or practiced. Awareness building, continuing education, centralised facility for quality assurance checks and rigorous quality administration are necessary to improve this situation.

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Various fractionated time dose models, such as NSD, CRE, TDF and LQ model are available for the treatment of malignant diseases. Recently polynomial model has been developed for fractionated as well as continuous radiotherapeutic treatments. In this paper, the polynomial model has been tested employing clinical data available for the head and neck cancers for fractionated radiotherapy. It is concluded that the clinical results are in reasonable agreement with the prediction of polynomial model.

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Several protocols had been proposed for calibrating high energy beam therapy machines. They require an accurate determination of physical parameters to convert depth ionisation to absorbed dose. The direct calculation of these parameters is quite a difficult task and time consuming. Alternatively, the dosimetric protocols had proposed tabulated values for these parameters. However, published data always don't agree with the values encountered in routine calibration. In this paper, semi-analytical expressions of the most important parameters, used in high energy electron beam calibration, have been derived. These expressions yield an alternative procedure for computing the various parameters instead of obtaining them from the published tables by tedious interpolations.

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