Technical note: thyratron performance--dependence on mounting in a medical linear accelerator.

A thyratron is an important component of a medical linear accelerator. The working life of a thyratron has been found to be dependent on its physical orientation in the accelerator. This observation is a result of maintaining accelerators for over 15 years.

Radiation, pepleomycin and hyperthermia in the therapy of locally advanced squamous cell carcinomas of the buccal mucosa.

Oral squamous cell carcinoma is the commonest male (29%) and the second commonest female (18%) malignancy in South India. At first attendance 93% of the tumours are stage T3 or T4. They are essentially locoregional, remote metastases being rare (0.75%). Radiotherapy alone yields a poor survival (19% 5 year NED). Radiopotentiation by chemical sensitizers and cytotoxic drugs has been attempted since 1960, the best results being obtained by a combination of irradiation and bleomycin. There was, however, persistent failure in about 40% of cases. The present three-armed trial attempted to improve the results of radiotherapy and bleomycin by the addition of hyperthermia. A total of 101 T3 and T4 buccal squamous cancers were entered in the trial over a period of nearly three years. Entry closed in August 1987 and the last case was evaluated in October 1987, hence only response data are available. Hyperthermia did not confer any benefit.

Local RF capacitive hyperthermia: thermal profiles and tumour response.

At the Cancer Institute we are using RF capacitive hyperthermia as an adjuvant to radiotherapy and/or chemotherapy in the local control of soft tissue sarcomas. We have studied the influence of bolus conductivity, electrode and phantom sizes on the rate of heating of agar phantoms. We have varied the bolus conductivity by varying the saline concentration in the bolus bags from zero to 2.0 per cent, during heating. We found that the rate of heating of phantoms increases and that of the bolus decreases with the increase in the saline concentration of bolus up to 1 per cent, irrespective of phantom and electrode sizes. However, for a given size of electrodes the rate of heating decreased with the increase in the phantom size. When the diameter and height of the phantom were equal to the diameters of electrodes the rate of heating of the phantom was nearly uniform. However, when the diameter of the phantom was larger than that of electrodes the rate of heating in the radial axis decreased with the increase in the radial distance. On the basis of this data we suggest the use of electrodes larger in size by 1.0-3.0 cm than the size of the tumour, where the size of the anatomical site to be heated is larger than the electrode size to be used. Phantom and clinical data have indicated that the presence of bone in the field of heating can lead to hot spots. Preliminary clinical results have shown that the response of sarcomas to thermo-chemo-radiotherapy was superior to that of either thermo-radiotherapy or radiotherapy alone.