Testicular dose and hormonal changes after radiotherapy of rectal cancer.
To measure the dose received by the testicles during radiotherapy for rectal cancer and to determine the contribution of each field of the pelvic box and the relevance for hormonal status. In 11 patients (mean age 55.2 years) testicular doses were measured with an ionisation chamber between 7 and 10 times during the course of pelvic radiotherapy (50 Gy) for rectal carcinoma. Before and several months after radiotherapy luteinizing hormone, follicle stimulating hormone and total testosterone serum levels were determined. The mean cumulative radiation exposure to the testicles was 3.56 Gy (0.7-8.4 Gy; 7.1% of the prescribed dose). Seventy-three percent received more than 2 Gy to the testicles. Fifty-eight percent of the measured dose was contributed by the p.a. field, 30% by the a.p. field and 12% by the lateral fields. Mean LH and FSH levels were significantly increased after therapy (350%/185% of the pre-treatment values), testosterone levels decreased to 78%. No correlation could be found between changes of hormones and doses to the testis, probably due to the low number of evaluated patients. Radiotherapy of rectal carcinoma causes significant damage to the testis, as shown by increased levels of gonadotropins after radiotherapy. Most of the gonadal dose is delivered by the p.a. field, due to the divergence of the p.a. beam towards the testicles. The reduction in testosterone level may be of clinical concern. Patients who will receive radiotherapy for rectal carcinoma must be instructed about a high risk of permanent infertility, and the risk of endocrine failure (hypogonadism). Larger studies are needed to establish the correlation between testicular radiation dose and hormonal changes in this group of patients.