[Time-dose relationship of erythema in high energy photon irradiation therapy]

Skin doses of 100 patients who were treated with high energy ionizing irradiation during conventional irradiation therapy were measured by thermoluminescence dosimeter (TLD). In 87 of the 100 patients, acute hyperemic change of the skin (erythema) of the irradiated region was observed. In the other 13 patients, alopecia of the scalp was observed. The following conclusions were reached. 1) The time-dose relationship was linear when erythema tolerance was used as an index, but not when alopecia was used. 2) The tolerance dose for erythema was lower than previously reported. The slope of the isoeffect curve on the log-log plot of total absorbed skin dose against total number of days after the first irradiation was 0.68 when erythema was used as an index. This number is larger than previously reported results. We considered that erythema is significantly influenced by fraction size and that hyperfractionation is a promising method of irradiation, especially in Japan. 3) Combined use of chemotherapeutic agents, such as 5-Fu, accelerated erythema. The slope of combined treatment was 0.86. Observing acute hyperemic change of skin is considered to be a useful method of investigating the combined effects of chemotherapeutic agents on irradiation.