Measurement of irradiated small bowel volume in pelvic irradiation and the effect of a bellyboard.

From June 1992 to January 1993, 51 consecutive patients with pelvic cancers treated with radiotherapy alone, or surgery plus post-operative radiotherapy, were included in a study of the effectiveness of a false table-top (bellyboard) in displacing small bowel loops out of anteriorposterior (AP) and posterioranterior (PA) opposing pelvic fields. The small bowel was opacified with barium. The volume of small bowel within the radiotherapy fields in the prone position with a bellyboard was reduced by 134-300 ml (29%-61%) when compared with that in supine position, and by 136-216 ml (28%-50%) when compared with that in prone position without a bellyboard, depending on the type of previous surgical procedures. The differences were highly statistically significant and likely to be clinically significant. The bellyboard we used is simple, economical, convenient and well tolerated. Its use is recommended, especially when AP and PA pelvic fields are used.