14C-lactose breath tests during pelvic radiotherapy: the effect of the amount of small bowel irradiated.

Thirty patients who were undergoing pelvic radiotherapy had 14C-lactose breath tests performed in the first and fifth weeks of treatment. In Group I (21 patients), a significant portion of the small intestine was irradiated, and in Group II (9 patients), only a small portion of the small intestine was irradiated. In Group I, the average reductions in the excretion of ingested 14C between the first- and fifth-week tests were 41.5% at 1/2 hour postingestion (p less than 0.05), and 21.8% at 1 hour postingestion (p less than 0.05). In Group II, the percentage reductions were 11.8% and 3.7% at 1/2 and 1 hour, respectively (p greater than 0.05). The data suggest that lactose malabsorption is a factor in the etiology of the nausea, vomiting, and diarrhea experienced by patients who are undergoing pelvic radiotherapy, and that the amount of bowel included in the treatment volume significantly influences the degree of malabsorption.