LYING-ON POSITION OF TOTAL SKIN ELECTRON THERAPY

Purpose: A technique for whole-body electron therapy with the patient in a lying position has been developed, This technique allows Total Sk in Electron Therapy (TSET) for those patients who were previously unab le to be treated in a conventional standing position. Methods and Mate rials: This study was carried out on a Varian 2100C linear accelerator with a 6 MeV high dose rate electron beam. The collimator was open to a width of 36 x 36 cm, There were two main procedures, with six dual- field techniques: 1) two static AP/PA vertical dual fields (VDF): the patient laid on the floor transversely under the collimator when the g antry was in a vertical position, A 0.6 cm acrylic board was placed 15 cm away from the patient, then the gantry was rotated 25 degrees cloc kwise end counterclockwise to treat the patient in the supine and pron e positions, respectively, 2) Four oblique junction fields (OJF): the patient laid on the floor in a prone and supine position parallel to t he wave guide at (227 - body thickness X tan 60 degrees) cm away from the vertical axis of the gantry, then the gantry was rotated 60 degree s toward the patient, A 0.6 cm acrylic board was placed 15 cm away fro m the patient perpendicular to the beam, The patient was move along th e field central axis, It allowed the patient's body to be within the 1 60 cm effective treatment profile, When the patient's body axis move 5 degrees toward the lateral side of the field central axis, we could o btain a better dose distribution in the vertex of the scalp and the so les of the feet, The angle of the VDF was measured by chamber detector s to obtain the effective treatment profile, Likewise, the optimal pro file for the OJF was determined by the same procedures, The Rando phan tom was used to measure the superficial dose of the body. Results: The dimension of effective treatment profile for the VDF was 188 x 72 cm at 87% dose level, For the OJF, we had to move the patient along the h eld central axis to obtain the effective treatment profile in a 180 x 85 cm dimension at a 87% dose level, The vertex and sole dose measured in this setup was in the range of 80-88%. Conclusions: The empirical data showed that the lying-on position for TSET was technically feasib le. The dose distribution in the body surface was also compatible with the Stanford standing technique, The nonambulatory skin malignancy pa tient can be treated in a comfortable and reproducible position. (C) 1 997 Elsevier Science Inc.