Critical organs and external irradiation in gynaecological cancers: can water be used as contrast agent to make easier the delineation of the small intestine?

Purpose. - To validate the use of water as contrast agent for the delineation of the small intestine on the planning CT of external beam in patients treated with conformal radiotherapy for gynaecological tumours. Patients and methods. - From March to September 2003, 20 patients received an external irradiation for a gynaecological carcinoma (13 with cervix carcinoma, seven with endometrial carcinoma) in the radiotherapy department of the Centre G.F. Leclerc of Dijon. The protocol of opacification of the small intestine consisted in administration of a 'negative' contrast agent: water. The protocol commonly used for the bladder filling, i.e. absorption of 500 cm3 of water from 60 to 30 min before the CT-scan, was applied for the evaluation of the visualisation of the small intestine in the 12 first patients (group I). For the last eight patients (group II), the absorption of the same amount of water was fractionated, every 10 min within half an hour before the start of the examination. Results. - The small bowel identification was possible in 100% of cases without any need of administration of a 'positive' contrast agent. In overall, the identification of the small intestine was considered as easy in 14 patients (70%) and as difficult in two patients (10%). In group I, the delineation was considered as easy in 50% of cases, moderately easy in 33% of cases and none easy in 17% of cases. Conversely, no difficulty was encountered for the definition of the small bowel in all patients of group II. Conclusions. - Water is an efficient 'negative' contrast agent for the differentiation of the small bowel from the colon on the planning abdomino-pelvic CT. Nevertheless, the delineation was really made easier only when the fractionated protocol of water absorption within half an hour before CT was used. (authors)