[Total cutaneous irradiation with low energy electrons and mycosis fungoides. Technic and dosimetry]

Mycosis fungoides initially involves the epidermis and the superficial layers of derma at a depth of about 1 cm. Wide field irradiation with low energy electrons is therefore the treatment of choice in the initial stages of the disease. In our Institute, total skin electron beam irradiation is delivered with Therac 20 linear accelerator: the lowest available energy is 6 MeV. A lucite sheet of 0.6 cm thickness is used to decrease the energy of the beam. We used film dosimetry to evaluate the homogeneity of dose distribution in an Alderson-Rando phantom with different arrangements of the fields and the lucite sheet: 4 and 6 fields techniques have been compared with different positions of the lucite filter, near the phantom and near the collimator. Six fields yield a better dose distribution: homogeneity is within +/- 3.7%, while with four fields it is within +/- 6%. X-rays contamination is less than 2%. "In vivo" dosimetry has been performed using thermoluminescent dosimeters: homogeneity is within +/- 15%.