A practical technique for conformal simulation in radiation therapy of pelvic tumors

Abstract

A radiological procedure, based on straightforward conventional methods, was used for a demonstration of pelvic anatomy during simulation to precisely delineate the target volume and increase the probabilities of pelvic tumor control. Between 1990 and 1993, 450 patients with primary pelvic malignancies underwent external radiotherapy by means of photons, 6-10 MeV, with multiple-field techniques. The simulation was carried out immediately following a pelvic organs opacification (POO) by standard methods. This procedure used a minimal quantity of contrast media (barium sulphate, iodine contrast) and metallic markers to locate directly and simultaneously: (a) small intestine, (b) bladder, (c) rectum, (d) anal canal, (e) bulbous male urethra, and (f) vagina. When all these structures were clearly visualized, the procedure was scored as successfully performed. The sensitivity of procedure was defined as the percentage of successful pelvic organs opacification (POO) carried out in the patients. It was 98% in both women and men. Indirectly, the procedure helped us to locate the prostate, the perineum, and the uterus cervix in the same percentage of patients. Pelvic organs opacification allowed us to document not only the normal position of the pelvic organs tested, but also any variations (ranging from 5% to 40% of cases, after pelvic surgery). Furthermore, POO revealed previously not-reported abnormalities in patients undergoing surgery, mostly rectal stenosis, urinary or anal incontinence, and bladder luxation. The cost of the materials used was $10-15 for each POO, and the time required 5-7 min. The side effects were 7% and not significant. In the simulation phase for multiple-field irradiation technique, the simultaneous visualization of pelvic organs obtained by POO procedure allows an exact positioning of the isocenter, an accurate shielding of structures, and finally, a reliable conformal therapy. Due to the low cost, the short length, and the insignificant side effects, POO can be carried out more than once during pelvic treatments for localization and verification of target.