Maximum and mean bladder dose defined from ultrasonography. Comparison with the ICRU reference in gynaecological...

The reference bladder dose for gynaecological intracavitary brachytherapy (BT), as defined by the ICRU 38 Report, is often criticised as it is seldom representative of the highest bladder dose nor it gives an idea of the area exposed to a significant dose. Since November 1990, ultrasound measurements are routinely made in order to determine the actual dose delivered to the bladder of each patient. The technique was as follows. (1) the bladder is filled up with 150-200 cm3 of sterile isotonic saline. (2) The intrauterine position of the tube is checked. (3) The bladder anatomy is controlled. (4) Points of measurements are identified: ICRU bladder reference, minimum distance between bladder mucosa, uterine tube and other similar measurements taken every 15 mm along the radio-active line. Maximum and mean doses are calculated at the sagittal plane. Measurements are performed by moving the transducer along the skin of the patient and included in the calculation of dose distribution. Doses delivered to each relevant point are compared. This enables determination to be made of the differences between the ICRU and the doses actually observed at the bladder wall with aid of ultrasonography. BT applications were checked in 58 patients (69 measurements). The method was feasible in all cases. The comparison between ICRU dose from orthogonal films and the ICRU dose from ultrasonography resulted in a 90% accuracy. The maximum and mean doses for utero-vaginal BT are higher than the ICRU dose in 75% of cases (range, 2-8). Measurements are now abandoned for vaginal applications as the ICRU dose only could be measured.(ABSTRACT TRUNCATED AT 250 WORDS)