Since 1989 a new protocol has been initiated for stage Ib, Ila and Ilb for radical irradiation of cancer of the uterine cervix. The irradiation consists of AP/PA external beam delivering 40 Gy in 20 fraction over 4 week period (includes initial 10 Gy open field and subsequent 30 Gy using 'wedge shaped mid-line block') and two intracavitary insertions, first at 2nd week of external irradiation and second at the end. The total dose delivered through intracavitary remains 60 Gy and 68 Gy to Point A for stage Ib, Ila and Ilb respectively. The wedge shaped mid-line block was designed using the dose distribution for Fletcher - Suit applicator of typical configuration of 13 7cs pellets. This block was designed such that the fall of dose rate with an intracavitary application between point A and point B has been compensated by external irradiation. This paper presents the design of the wedge shaped mid-line block, dosimetric measurements and its advantages over conventional rectangular block.

Electron beams from an accelerator appear to come from a point in vacuum designated as virtual source that lies at a distance not coinciding with the scattering foil or the beam exit window. This is due to the influence of the various scattering processes taking place in the foils, collimator and the electron applicator apart from the fringe magnetic fields in the blending magnet. Virtual source to isocentric distances are experimentally determined by measurements made in a polystyrene phantom using an ionization chamber and applying inverse square law. The results for the narrow and broad beam geometry are presented for the electron beams available with Clinac-1800.

The conventional intra cavitary treatment of cancer cervix with pre loaded or after loaded applicator with Radium, Cs or Cobalt 60 are being replaced by selectron after loading systems. The dose-rate for Brachytherapy is changed from over 0.5.Gy per hour to about 1.7 Gy per hour and because of this change the dose to be delivered by intracavitary insertion is to be reduced by an appropriate percentage. Using clinical data published so far, a suitable correction factor is arrived at. Even though the correction factors used in various clinical work appear to be varying they fall more or less on smooth curve which gives the correction factor to bring about same normal tissue late reactions. A similar curve has also been obtained to give the same tumour control when selectron is used in the range of 1.5,Gy per hour to 2.0 Gy per hour. Appropriate correction factors are 42 and 47% respectively.

The effect of radiation detector positioning over liver and spleen containing Fe-59 radioactivity, on its response has been investigated using water filled PVC elliptical cylinder as upper abdomen (UA) phantom and lucite Alderson phantoms of liver and spleen. Significantly large and rapid variation was exhibited when the detector moved around the reference point over the spleen. No significant difference in response could be found when the detector moved around the reference point over the liver. The effect of organ volume on detector response as well as on its contribution in the count rate of neighbouring organ was investigated using rubber balloon of appropriate volume. As a consequence of the study it was possible to mark on the abdomen phantom an area wherein if the detector pointed to spleen measurement, the contribution from liver radioactivity in the form of scattered radiation will be < 15%.

Among the man-made sources of ionising radiation medical X-ray units contribute the highest radiation dose to the public12. In Kerala too the fact remains the same where 150 X-ray examinations are conducted per 1,000 people every year and more than 3.6 million people per year undergo X-ray investigations3. The X-ray doses received were in the range of 0.5 mSv to 30 mSv with a very large standard deviation. Patient doses in respect of a wide variety of X-ray investigations are actually measured and presented.

In the radiotherapy of cancer of oesophagus and cancer of bladder, the necessity of three field arrangement is very common. If the patient is positioned in supine position, then during posterior oblique field treatments the mesh frame of the table top in telecobalt machines such as Th-780, Th-780C and PHOENIX, intercepts the field. As this is only a geometrical situation, whether the mesh frame intersects the beam or not is given in the from of a mathematical condition. In case the aluminium frame intercepts the radiation field then an alternative arrangement has to be employed.

131I-Rose bengal clearance test has been immensely used for the clinical assessment of functional hepatic abnormalities. It has been observed that external collimated scintillation probe employing 131I-Rose bengal is a rapid and less erroneous way of assessing polygonal cell function in liver. The present study demonstrates the protection of liver by Liv-52 from the deleterious effects of carbontetrachloride (CC14) by determining the biological half-life of 131I-Rose bengal in male albino rats. An increase in the biological half-life of the radio-iodinated dye was observed following CC14 intoxication which was reversed by Liv-52 treatment.

A comparison between the measured values of leakage radiofrequency (rf) power density from the diathermy units which have been in use for long time and those commissioned recently, shows that usage and aging does not significantly increase the leakages from diathermy units. Observed leakage densities are however higher than those reported during such studies by international bodies. With increasing use of radiofrequency and microwave radiation in research, industry and medicine, it has become imperative that a programme of safety studies and surveys around facilities using (rf) radiation be kept alive. it is then easier to point out cases of faulty equipment and work practices which result in excessive exposures.