Dose Measurements in the Treatment of Mycosis Fungoides with Total Skin Irradiation using a 4 MeV Electron Beam

The total skin irradiation (TSI) is one of the most efficient techniques in the treatment administered with curative intent of the cutaneous T-cell lymphoma (mycosis fungoides). The cure may be obtained in 10% to 40% of the cases [13]. To irradiate all skin in an appropriate time of the machine, in most times, are used large electron fields with treatment distances about 3 meters. The original Stanford University technique [4], created in 1960, in which they irradiated the patient in all longitudinal extension, was applied in a 4.8 MeV linear accelerator, that provided 2.5 MeV electrons in the patient, by the use of 4 couple beams with the patient placed in front of the beam, 3 meters distant from the accelerator. In this work we describe a 4 MeV electron beam treatment method based on Stanford technique, where we used a Varian linear accelerator CLINAC 2100. We intend to improve the uniformity of the dose and to reduce the treatment time to the patient and also to reduce the problems with the overlapping treatment fields that occurs in conventional treatment that uses 1 meter of focus-skin distance. For this method the patient is placed on a rotative base and he assumes successively 6 positions: stand up and perpendicular to the beam, distant 2.83 meters from the source, with 60 degrees of interval between the rotations. In each position, the patient is irradiated by a couple of beams (the beam angulation is 19.5 degrees above the transversal axis in the middle of the patient and 19.5 degrees below it), figure 1a. A rotatory base makes easier the rotation of the patient, figure 1b.