As the telecobalt machines are made with different collimator designs, knowledge of the build-up profile and effect of different intervening materials in the beam is necessary. In this study, the build-up dose measurements were performed in different telecobalt machines using a PTW parallel plate chamber. Results from the study showed that the surface dose drastically increases with the presence of lucite tray in the path of the beam at short SSD. However, the effect is not significant at longer SSDs. Also, any conventional long SSD machine. when used for short SSD treatment will result in clinically adverse skin reactions. The introduction of a 2.8 mm lead plate improves the beam characteristics at short SSD with clearance of 10 cm to surface level. The result has relevance in the design of suggested short SSD telecobalt machine in lndia for the treatment of head and neck cancers.

Head scatter correction factor (Sc) is used to account for in-air variation of the output of mega voltage photon beams. The magnitude of Sc depends on the construction and material of source head of the teletherapy unit, depth of measurement, interchange of collimator jaws and introduction of beam' modifying wedges. SC for four telecobalt models, Theratron 1000E, Theratron 780E, Theratron 780C and Theratron Phoenix, were measured to study (a) the effect of contaminating electrons on the value of Sc measured at the depth of dose maximum (dmax); (b) collimator exchange effect on the value of SC; (c) effect of beam modifying wedges on the values of Sc; (d) unit-to-unit variation of Sc for the same model of the telecobalt machine; and (e) variation of Sc with different models of the telecobalt machines of same manufacturer. Results of these measurements indicate that the effect of contaminating electrons on the value of SC measured at dmax, the colimator exchange effect and the effect of wedge filters on the values of Sc are within the experimental uncertainty and can be neglected. However, the variation of Sc with different units of the same model and with different models of the same manufacturer of the telecobalt machine is larger than the experimental uncertainty and hence Sc data or clinical use should be measured with each and every unit of the telecobalt machine.

The aim of this work was to estimate dose homogeneity inside the body during total body irradiation and to check the agreement between doses calculated and those measured in vivo for the applied method of irradiation. 30 patients were input into the dose comparison. The irradiation was performed with a Co-60 unit. Six lateral and two anterior-posterior fields were applied. Calculations and measurements were carried out for ten transverse cross-sections representing different body parts and organs. Doses were measured with thermo luminescent, semiconductor and ionization detectors. Dose deviations inside the patient's body, along the body midline, ranged between -0.8% and + 7.9% in relation to the prescribed dose, and those outside the midline ranged between -1.6% and + 8.7%. Standard and percent deviations from the prescribed dose for the whole group of patients exceeded 10% at the neck and the lung sections only.

Scientific community has depended on the BJR Supplements on central axis depth dose data published from time to time. There have been five Supplements since 1953 when Supplement No. 5 was first published on the subject. The frequent revisions, addition of new data and updating with the technological advancements are special features of these Supplements. The most recent Supplement is numbered 25 and has been brought out in 1996. A review of the data in respect of Co-60, MV X-rays and electron beams as described in the Supplements is the subject matter of this write-up.

In many radiation therapy centres, particularly those involving larger treatment regimes, non-treatment days can be a significant proportion of the total. In this context, this paper discusses the necessity to maximize the effectiveness of time-dose relationship in clinical setting. A strategy of post-gap acceleration involving fewer radiobiological difficulties is advocated as the choice for compensation of gaps.

Brachytherapy using iridium-I92 HDR remote afterloading system is a fast developing modality being witnessed in modern radiation therapy. The dose distribution of HDR interstitial implants are controlled by a single high activity Iridium-192 stepping source by changing the dwell times. The purpose of this paper is to bring out the important physical, technical and dosimetric aspects of high dose rate (HDR) interstitial implants for carcinoma breast. A dosimetric comparison of the Stepping Source Dosimetry System (SSDS) and Paris System of implants revealed that the SSDS offers more uniform dose than the Paris System of implants traditionally used for low dose rate brachytherapy applications. Also, SSDS demands less number of catheters compared to Paris system for a given target volume. The analysis of natural Dose Volume Histograms (nDVH) eliminates the error in the dose delivery by correcting the dose prescription and normalisation.

In view of the potentiality of electrets radiorespirometry already established for rapid detection of the microorganisms, further standardisation and the technical refinements were done. The technique was evaluated and validated on a large number of test urine samples apart from the comparative evaluation with regard to conventional microbiological method. The matched results were found in about 82.5% out of the total number of 200 test samples evaluated and estimated. The technique was found to be equally validating for the commonly encountered microorganisms, namely E-Coli, Staphylococcus aureus, Pseudomonas and Klebseilla in serial assay batches. The technique was also found to be effective in rapid detection of the microorganisms present in the relatively lower inoculum size.