Tangential radiotherapy portals' with cobalt-60 gamma radiations are widely used in the management of post- operative breast cancer. The treatment planning and dosimetry are complex because of the obliquity and irregular contours. A method followed at our centre makes use of selected percentiles covering the tumour volumes for various preselected inter-field separations. Equivalent field concept is used for the half-blocked portals. Comparison with computerised plans and phantom measurements validate the outlined concept.

The paper deals with dose distribution studies with FBX dosimetric system in a monkey cage, in a simulated chest phantom and a circular plastic phantom. These types of studies are helpful in delivering dose to patients and experimental animals with a Cobalt Teletherapy source.

The conventional radiation sources have been replaced by 192Ir wires in interstitial brachytherapy because of its obvious advantages. The common technique adopted using 192Ir wires, in many anatomical sites, is with flexible nylon tubes and buttons. This technique has limitation where the tumour can be approached from only one. side like in the perineal region. The use of templates has an advantage of good geometry and homogeneous dose distribution around the target volume. One of the common templates used is the Prostate template, used for several sites in the perineal region. To get an idea of dose distribution in several dosimetric planes treatment planning system is essential. However this method is not practiced in the centres not having facility of computerized treatment planning system. This paper describes a simple method to carry out manual dosimetry, which can give a equitable results with the computerized dosimetry.

Many international organizations recommend to carry out dosimetry in water phantom at 5 cm depth to arrive at dose at the depth of maximum buildup using percentage depth dose or tissue air ratio data. These recommendations minimize error in dosimetry due to contribution of low energy components of photons at maximum electronic equilibrium depth, which mainly depend upon collimator design of telecobalt units. Some centres may not be able to adopt water phantom dosimetry because of non-availability of water phantoms. In this paper a method has been described to determine the absorbed dose in water for various field sizes using a single value arrived from air measurement and an empirical equation. The empirical constants for the equation are generated for three types of telecobalt units. The results obtained from empirical equation and water phantom dosimetry are found to match closely.

In India significant percentage (25%-30%) of cancer patients are to be treated for head and neck sites where there is no need for rotational techniques. The field sizes are also small. A dedicated short SSD (40 cm) cobalt machine with 74 TBq (2000 Ci) capacity appears to be relevant and cost effective. If suitably designed, these machines could make use of decayed cobalt sources removed from long SSD models. If skin-sparing effect is preserved at short SSD, there is definite scope for such machines in the treatment of cancer patients. The possible design feature of such machine is highlighted

Interstitial brachytherapy as a treatment modality for the malignant lesions is gaining increasing interest. Tables and nomographs have been suggested and are being used for manual dosimetry. In this paper some empirical equations are suggested for the computation of basal dose-rate (BDR) for standard single and double plane implant geometry based on Paris system. These equations, however, can also be used for finding the inter-source spacing or inter-plane spacing for a given linear activity and reference dose-rate to get the optimal implant geometry.

In this paper the hardware design of an Applied Potential Tomograph system developed at BARC is presented. It comprised of a data acquisition unit, an interface unit and a personal computer. Data acquisition unit measures mutual impedance values between adjacent electrodes by passing sinusoidal current in different directions. The mutual impedance value along with lead configuration number and gain value are read by personal computer through interface unit. Mutual impedance values obtained from Phantom for different conductivity distributions are shown to be significantly different.

lntracavitary brachytherapy by afterloading technique is the choice of the treatment for carcinoma of cervix. The dosimetry of the intracavitary brachytherapy is complex in the sense that the optimal dose that can be delivered to the tumour is dictated not only by the volume and extent of the tumour but also by close proximity of the dose limiting structures, such as the small and large intestines, rectum and bladder. Dosimetry of the rectum is comparatively easy as compared to bladder dosimetry. We have done measurement of bladder dose in 10 patients undergoing intracavitary brachytherapy applications. The Ferrous Sulphate - Benzoic Acid - Xylenol Orange (FBX) chemical dosimeter system was used as a filling solution in the Foley's catheter bulb for bladder dosimetry in place of distilled water. We observed the bladder dose to be 10.5-12.5 Gy for a point A dose of 30 Gy.

Irradiation of human peripheral blood lymphocytes at Go with 3 Gy of 60Co gamma rays induced chromosomal aberrations such as dicentrics and acentric fragments whereas hyperthermic treatment at 37 43°C for 20 min by water bath immersion produced no such effects. When cells were heated at 43°C for 20 min at various time intervals (1-180 min) after exposure to 3 Gy, the frequency of dicentrics was greatly reduced immediately (1 min) after irradiation compared to cells exposed to radiation alone. The number of dicentrics however, increased to that of cells treated with only radiation when the interval between the two treatments was 20 min or more indicating rejoining of radiation induced chromosome breaks within this period. Acentric fragments and total breaks increased significantly when cells were heated immediately after irradiation but decreased thereafter to control values. Post-irradiation heating at 41'C also reduced the frequency of dicentrics. These studies thus indicate that hyperthermia enhances radiation induced chromosome damage by inhibiting post-irradiation rejoining of chromosome breaks

Glutathione (y - glutamyl cysteinyl glycine, GSH) constitutes the major low molecular weight thiol compound in the mammalian cells. GSH has been assigned an important role in determining the inherent radiosensitivity of cells. Endogenous GSH is involved in a number of radiation induced chemical processes, which help in the repair of radiation injury to the target molecules. Experimental evidence suggests that GSH competes with molecular oxygen in the cells to prevent fixation of DNA damage. Certain chemicals like buthionine sulfoximine are found to deplete the cellular GSH content by interactions at specific sites in the GSH cycle. It may be possible to take advantage of this phenomenon by increasing the radiosensitivity of hypoxic tumor cells, without seriously affecting the normal cells, so as to increase the therapeutic efficiency of radiation treatment