In vivo urethral dose measurements: A method as verify high dose rate prostate treatments

Radiation doses delivered in high dose rate (HDR) brachytherapy are suscept ible to many inaccuracies and errors, including imaging, planning and deliv ery. Consequently, the dose delivered to the patient may deviate substantia lly from the treatment plan. We investigated the feasibility of using TLD m easurements in the urethra to estimate the discrepancy in treatments for pr ostate cancer. The dose response of the 1 mm diam, 6 mm long LiF rods that we used for the in vivo measurements was calibrated with the Ir-192 HDR sou rce, as well as a Co-60 teletherapy unit. A train of 20 rods contained in a sterile plastic tube was inserted into the urethral (Foley) catheter for t he duration of a treatment fraction, and the measured doses were compared t o the treatment plan. Initial results from a total of seven treatments in f our patients show good agreement between theory and experiment. Analysis of any one treatment showed agreement within 11.7%+/-6.2% for the highest dos e encountered in the central prostatic urethra, and within 10.4%+/-4.4% for the mean dose. Taking the average over all seven treatments shows agreemen t within 1.7% for the maximum urethral dose, and within 1.5% for the mean u rethral dose. Based on these initial findings it seems that planned prostat e doses can be accurately reproduced in the clinic. (C) 2000 American Assoc iation of Physicists in Medicine. [S0094-2405(00)02510-4].