Transrectal ultrasonography for prostatic cancer. II. The response of the prostate to definitive radiotherapy.

Transrectal ultrasonography was used to monitor the response of adenocarcinoma of the prostate to radiotherapy before and 6 to 15 months after treatment combining implantation of radioactive gold seeds with external beam irradiation. Data gathered before and after irradiation therapy suggested that the two most sensitive measures for monitoring the primary tumor are the calculated volume of the prostate and the integrity of the prostatic capsule. The calculated volume of the prostate decreased significantly in all patients by 6 months after radiotherapy. The rate and degree of reduction correlated significantly (P less than 0.05) with the histologic grade of the tumor (poorly differentiated tumors shrinking most rapidly), as well as with the outcome of treatment (P less than 0.05). However, there was no such correlation with stage. After treatment, the average number of sites of capsular disruption decreased steadily, reaching 50% of the pretreatment number by 15 months. Transrectal ultrasonography is a practical, inexpensive, noninvasive tool for monitoring the response of prostatic cancer to definitive radiotherapy, and may provide a means of identifying patients who will respond poorly to treatment.