The lack of impact of pelvic irradiation on small bowel mobility: implications for radiotherapy treatment planning.

PURPOSE

Small bowel contrast is frequently used during simulation for patients undergoing pelvic radiotherapy to assist in the design of blocks that exclude small bowel from the radiation field. In many instances, a large field is treated to 45 gray (Gy), followed by a field reduction to exclude the small bowel. This prospective study was designed to assess whether the position and mobility of the small bowel changed after the initial 45 Gy, thereby determining whether a special small bowel series done at initial simulation is applicable at the time of field reduction.

METHODS AND MATERIALS

Twelve patients undergoing pelvic irradiation were given small bowel contrast for their initial simulation. Radiographs were taken with the bladder empty and the bladder full. The location of the small bowel and its displacement with bladder distention was measured. This entire procedure was repeated prior to field reduction (after 39.6-46.0 Gy).

RESULTS

There was no demonstrable alteration in small bowel mobility after 39.6-46.0 Gy. The approximate position of the small bowel relative to bony landmarks was unchanged.

CONCLUSION

The position and mobility of the small bowel appears not to be affected by 39.6-46.0 Gy of pelvic radiotherapy. Therefore, it is reasonable to design reduced pelvic fields to exclude the small bowel based on special small bowel series done at initial treatment simulation.