Hyperthermia response and thermotolerance capacity of an experimental rat tumour with occluded blood flow.

Thermotolerance in vivo was investigated using the rat fibrosarcoma SSBla. Hyperthermia was administered using water-bath heating, with the tumour blood supply occluded by clamping during the heating procedure. Single-dose heat treatments (10-60 min at 43.5 degrees C) yielded linear dose-response curves, with response evaluated as tumour re-growth delay. In thermotolerance studies split-dose treatments were given in which a single 'priming' treatment of 30 min at 43.5 degrees C was followed 24 or 48 hr later by a variable treatment (10-90 min), again at 43.5 degrees C. Split-dose responses produced generally less uniform results, though the dose-response curves were still approximately linear. Comparison of the slopes of the dose-response curves for single-dose and split-dose treatments gave a 'thermotolerance ratio' (TTR) of 4.09 and 3.45 at 24 and 48-hr intervals respectively. Data analysis using Monte Carlo simulation techniques also suggests that the distribution of tumour sensitivities to a second heat treatment may be considerably broader than the distribution of sensitivities to a first treatment. Uniformity of tumour response to a single heat treatment may therefore conceal a spectrum of capacities for development of thermotolerance amongst individual tumours.

Seventh interim progress report of the british institute of radiology fractionation study of 3F/week versus 5F/week in radiotherapy of the laryngo-pharynx.

A fresh analysis of the data entered into the multicentre BIR fractionation trial of 3F/week versus 5F/week in radiotherapy of the laryngopharynx has been undertaken. Completed records of the 732 patients initially entered into the trial have now risen from 687 at the last report to 706. The data have been analysed in a manner similar to that adopted previously so as to measure the effects of the two regimes on both tumour and normal tissues, and some additional analyses have now also been made. There have been some modifications in the results in the various sub-groups which may be due to an inadequate number of patients having been followed up for long enough at the time of the previous analyses. More data for late radiation damage to normal tissues and new radiobiological findings have suggested possible explanations for the differences which have emerged between the two groups. The apparent differences between the sub-groups containing patients with highly localized tumours, which were reported in our previous report, are now less marked and not statistically significant.

Temperature distribution in tissues subjected to local hyperthermia by RF induction heating.

We have used a finite difference formulation of the bio-heat transfer equation to predict temperature distributions in and around a non-uniformly perfused volume located in layered tissue. Using available data on blood flow in experimental tumours we have shown that techniques capable of highly localized heating are required to treat small, well perfused tumours effectively. However, the r.f. technique considered here produces acceptable temperature distributions in larger tumours with poorly perfused centres. Skin cooling improves the effective penetration of the hyperthermal treatment and may improve the uniformity of heating. However, the considerable heat flux through superficial tissues associated with chilled water cooling can produce large temperature gradients in such regions.

Considerations of radiofrequency induction heating for localised hyperthermia.

A finite difference technique for studying both spatial and temporal variations in temperature in tissues subjected to local hyperthermia is described. The calculation offers speed and simplicity whilst remaining stable. Its form is discussed in both 3-dimensional Cartesian coordinates and cylindrical coordinates. The technique is used to predict RF induction heating of a plane skin-fat-muscle model. Physical and physiological parameters are incorporated. These include the contributions to heating from both E and H fields associated with a plane coil, heat transfer across the skin surface for various environmental conditions, and an appropriate dependence of blood flow on temperature for each tissue layer. The effects on tissue temperature of varying each of a number of parameters in the model are considered.

The response of murine lymphoma cells - L5178Y S & R - at heat at 44 degrees C.

Two murine lymphoma cell lines L5178YS and L5178YR were exposed to heat at 44 degrees C. In comparison with other cell lines there were found to be among the most sensitive to the lethal action of heat studied to date. The difference between these cell lines in response to heat was very small when compared to the differences observed with ionizing radiation. The pattern of leakage of radiolabelled leucine at 44 degrees C was measured in each cell line and small changes compared with the behavior at 37 degrees C were observed. No net breakdown or loss of preformed protein was observed during heating nor did any labelled protein leak from the cells.