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Hyperthermia combined with 60Co gamma irradiation was studied using V79 hamster cells cultured in vitro. Modest hyperthermia (41 degrees C for 6 hrs.) enhanced the cell killing produced by acute exposure to radiation. The same treatment enhanced the effect of low dose-rate irradiation (200 rads/hr.) even more. The sequence in which modest hyperthermia was combined with low dose-rate irradiation was important. Maximal enhancement was observed when hyperthermia was followed by irradiations. The probable explanation is that, by damaging the repair system, prior heat renders the cells unable to repair sublethal damage during subsequent low dose-rate irradiation.

The penetration, scattering, and absorption of electron beams of energy 10 to 20 MeV in water has been mathematically investigated by solving the Lewis equation by the moment method under the continuous slowing-down approximation. Two beam geometries were considered: plane infinite monodirectional beam and point monodirectional beam, both incident on an infinite water medium. For the former, expressions were obtained for the flux, current, rate of energy deposition, rate of charge accumulation, and angular distribution as a function of depth, taking into account not only the incoming primary electrons, but also the contribution of the secondaries. For the latter geometry, expressions were obtained for the rootmean-square average of the flux and energy deposition as a function of depth.

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