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 Skin Electron Therapy (TSET) for those patients who were previously unable to be treated in a conventional standing position.

METHODS AND MATERIALS

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 gantry 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 clockwise and counterclockwise to treat the patient in the supine and prone positions, respectively. 2) Four oblique junction fields (OJF): the patient laid on the floor in a prone and supine position parallel to the 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 degrees toward the patient. A 0.6 cm acrylic board was placed 15 cm away from the patient perpendicular to the beam. The patient was move along the field central axis. It allowed the patient's body to be within the 160 cm effective treatment profile. When the patient's body axis move 5 degrees toward the lateral side of the field central axis, we could obtain a better dose distribution in the vertex of the scalp and the soles of the feet. The angle of the VDF was measured by chamber detectors to obtain the effective treatment profile. Likewise, the optimal profile for the OJF was determined by the same procedures. The Rando phantom 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 field 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 feasible. The dose distribution in the body surface was also compatible with the Stanford standing technique. The nonambulatory skin malignancy patient can be treated in a comfortable and reproducible position.