Irregular body surface of the patient give rise to inhomogeneous dose distributions around the target volume. Homogeneous dose distribution can be obtained using tissue compensators. Preparation of tissue compensators with aluminium or lead blocks is a tedious method and commercially available devices are expensive. A compensator device has been designed to use a tissue equivalent material to be kept at shield tray level, which accounts for divergence of radiation beam. The reduced size of such tissue compensator obtained at much longer distance from the skin exhibits minimum risk of electron contamination. Experimental verifications were carried out for a tissue compensator by determining transmission at different off axis points for confirmation of the accuracy of the device. This paper presents the design of tissue compensator device and methods to prepare the tissue compensators using tissue equivalent materials.

A retrospective analysis of 291 patients with cancer of the uterine cervix treated with a combination of external and intracavitary radiotherapy was carried out. Patients were treated with external radiotherapy dose of 45 Gy in 20 fractions, 5 fractions per week or 42 Gy in 14 fractions, 3 fractions per week. For brachytherapy the total dose was 24 to 32 Gy at a dose rate of'1. 4 to 2.2 gy per hour. Treatment results in terms of response, survival, recurrence and complication were correlated with total Extrapolated Response Dose (ERD) values for point A (ERDTA) and for rectum (ERDT,). ERDTA values did not correlate with response, recurrence and survival rates (p value >0.05). ERDTA values correlated well with rectal complication rate (p value >0.025). Lack of correlation was observed between ERDT, with rectal complication rate (p value >0.1). In order to limit Grade II and Ill rectal complications to acceptable level, in combined external and intracavitary treatments, ERDTA value of less than 93 is suggested.

With the advent of monoclonal antibodies and the trend towards simple extra laboratory tests a very wide variety of alternative immunoassays are booming in the present day market, even though immunoassay principle basically originates from radio immunoassay. Comparisons are made between radioimmunoassay and alternative immunoassay on various aspects. Radio immunoassay is better than alternative immunoassay.

The application of linear quadratic (LQ) model to biological effects of radiation is known for at least three decades. In case of radiotherapy in order to ensure that appropriate tumour lethal dose is delivered without exceeding normal tissue tolerance, concepts like NSD and its derivatives were used in the past. Due to their shortcomings these concepts are now replaced by a linear quadratic model. As this model is based on the recent radiological data, it is claimed to be able to predict the biological responses of tumours as well as normal tissues more accurately. However, the accuracy of prediction depends on the precise values of various parameters that are involved in the linear quadratic equation. For most of the tumours and the associated normal tissues, values of the parameters are not yet accurately known. The parameters involved are alp the repair constant and repopulation factor. From radiobiological data on animals, in-vitro experiments on tumour cells and clinical data values of these parameters have been compiled and presented in this paper. It is found that the parameters are very much different from tissue to tissue and site to site. Large number of clinical data will have to be analysed to obtain precise values of these parameters so that LQ model can really be as accurate as it is promised to be.

Delayed renal scintigraphy, beyond usual 30 min dynamic study period, is commonly used for evaluation of urographically non-opacified kidneys. However, optimum time at which these urographically 'absent' kidneys will appear on nuclear imaging is controvertial. It has been observed that if a kidney is not seen up to 4 hrs, it is unlikely that it would be seen later. Mathematical modelling of scintigraphic visualisation data using parabolic and exponential functions have been done. Parabolic function which apparently represents the best-fit model for temporal spectrum of scintigraphic visualisation reveals that the cut-off time beyond which kidneys are not seen is t = 4.535 hrs. Zeros and maxima for both the functions were calculated and the merits and demerits of these modelling functions discussed.