Measurement of dose rate at the interface of cell culture medium and glassdishes by means of ESR dosimetry using thin films of alanine

Previous studies on human cervical cancer cells (NHIK 3025) have indicated that the cells, when X-irradiated in suspension, appeared to be more radios ensitive than when they were irradiated attached to glass dishes. However, this result depends on dosimetry, which is difficult in the situation where cells are attached to glass dishes due to backscattering electrons at the glass-liquid interface. Recently developed dosimetry that is based on detec tion of radiation-induced stable radicals in alanine and uses ESR spectrosc opy offers a possibility for more relevant dosimetry at the glass-liquid in terface than the previous estimates of doses based on Fricke dosimetry. Thi n alanine films (greater than or equal to 10 mu m) were used to measure dos e at the interface by irradiating the films while they were placed tightly against the bottom of dishes and covered with 1 mm of was simulating the me dium above cells, Fricke dosimetry was also performed, with different depth s of Fricke solution in the dishes, to elucidate the contribution to the do se delivered by backscattering electrons at the glass-liquid interface. A d ose rate of 1.9 Gy/min was measured with a thin layer (0.2-0.3 mm) of Frick e solution in petri dishes made of glass. However, this estimate appears to be too high, due to a contribution to dose by short-ranged electrons gener ated when the X rays passed through a steel lid 4.5 cm above the dishes. Do simetry using alanine films resulted in dose rates of 1.15 and 0.87 Gy/min at the interfaces of glass-liquid and plastic-liquid, respectively, Hence t here is a significant contribution to dose from backscattering electrons on dishes made of glass. The reason for our previous observation of a differe nce in radiosensitivity between cells irradiated in suspension and cells ir radiated attached to glass appears to be a lack of accurate dosimetry at th e glass-liquid interface. (C) 1999 by Radiation Research Society.