A technical device in low dose rate brachytherapy with IR-192 thin wire for localized prostatic carcinoma

Purpose: Ir-192 thin wires were used in our hospital since December 1997 for low dose rate brachytherapy for prostatic carcinoma. Since February 2000, we used the therapeutic planning system which created a pattern of dose distribution from a transrectal echogram, however, there were difficulties associated with this treatment which we tried to improve. However, a technical problem with the Ir-192 low dose rate brachytherapy became obvious. Improvements to the method have been tried since October 2001, and are reported here. Method: We performed brachytherapy for localized prostatic carcinoma on 105 patients from February 2000 to February 2003. We defined the period from February 2000 to September 2001 as the early phase (47 cases). The period from October 2001 to February 2003 was defined as the late phase in which technical improvements were introduced (58 cases). We compared the late phase with the early phase. The early phase treatment procedure is as follows. We did centesis with a plastic needle for the prostate gland using transrectal ultrasound as a guide through the aperture of a template by a transperineal approach. The position of the paracentesis needle was checked by CT and also obtained a pattern of dose distribution in 2 dimensions from the maximal profile of the prostate gland. This was analysed and dose rate calculated and radiation source halt time. We set the clinical target volume around the circumferential part of the prostate gland. We inserted radiation source in a pallium needle and then fixed them in situ. However, the next points were modified. 1) We changed the posture of a patient into extended lithotomy. 2) We invested the position of the transrectal ultrasound probe in a part of infraversion/dorsum. 3) A metal marker was inserted into the apex of the prostate gland and was maintained. 4) We contrasted the urethra by means of transrectal ultrasound. 5) The calculated dose distribution from the transrectal ultrasound for therapeutic planning could be obtained in 3 dimensions. The dose volume histogram was calculated in relation to the prostate, urethra and rectum from which we decided the dose rate. Each technical improvement was evaluated. Result: 1) The loading of the needle, which avoided the pubic arch by taking the extended lithotomy was enabled. 2) Visualization enabled a good amount of the border area of the prostate gland by positioning of the transrectal ultrasound probe moving towards the dorsum. 3) We inserted a metal marker at the gland apex part in order to aim the radiation source displacement and maintain it. 4) It became easy to identify the urethra by contrasting it. 5) We devised a configuration of paracentesis needle. It became technically clear that the dosage to the urethra and the rectum could be decreased by these improvements. Conclusion: We evaluated the problem of brachytherapy for localized prostatic carcinoma with a low dose rate Ir-192 thin wire. We introduced technical improvements to improve treatment. This has provided a reference point for further technical improvements for brachytherapy for prostatic carcinoma.