[The belly-board technic for the sparing of the small intestine. Studies on positioning accuracy taking into...

The immobilization error of patients positioned on the open table-top device in prone position as well as the movement of the small bowel out of the pelvis by this positioning technique was determined. The positioning error is of special importance for the 3-dimensional treatment planning for conformational radiotherapy.

The positioning error was determined by superpositioning 106 portal films with the corresponding simulator films from 21 patients with carcinoma of the rectum who-received 3D-planned conformational radiotherapy (3-field technique with irregular blocks). The movement of the small bowel out of the pelvis was studied by comparing simulator films after barium swallow in supine and open table-top position as well with 3D-treatment plans of the same patient in both positions in 3 cases.

The positioning error along the medio-lateral, dorso-ventral and cranio-caudal axis was 1.4/0.6/1.8 mm and the standard deviation 4.4/6.8/6.3 mm, respectively. In comparison to the supine position more rotation errors in the sagittal view were observed (37% and 9% respectively) with a median of 5.1 degrees. Six out of 22 patients showed no adhesions of the small bowel and a complete movement out of the treatment field was achieved. 14 out of 16 Patients with adhesions revealed a partial movement of the small bowel out of the treatment field. Comparing 3D-treatment plans in both positions again demonstrated a marked reduction of the irradiated small bowel volume with the use of the open table-top device.

The open table-top device positioning technique is a simple and cheap positioning support to reduce small bowel obstructions by radiation therapy of pelvic and retroperitoneal tumors. For the radiation treatment planning the data suggest a safety margin to compensate positioning errors of approximately 1.5 cm referring to the 95% confidence interval.