[The gonadal loading during the irradiation of lymph outflow in operated seminomas. In-vivo dosimetry].

Background: This article should demonstrate the problems concerning gonadal dose in seminoma patients, the impact of shielding and possible consequences for therapy and advising of patients with desire to have children.

Patients And Method: Since November 1993 gonadal doses of 43 patients (Stage I/II, Royal Marsden) have been determined in 80 measurements with 2 ionization chambers on the ipsi- and contralateral side of the remaining testicle. The patients were all treated with ap/pa "hockey-stick"-shaped fields on a 6 MV linear accelerator. With single doses of 1.8 Gy in midplane, total doses of 34.2 Gy were applied in 13, and 30.6 Gy in 30 men. Protection was used in 33 patients, 6 times with conventional shielding, later plus an additional clam-shell from ap. The results of 22 measurements on 6 men with and without protection are of special interest. In 25 patients a sperm analysis before radiotherapy was conducted.

Results: Before the beginning of radiotherapy (RT) 56% of available patients have shown an impaired spermatogenesis. The mean gonadal doses were 2.4% of midplane dose-MD (4.8 cGy), 1.8% MD (3.2 cGy) and 1% MD (1.8 cGy) per fraction for patients without (n-patients = 10, m-measurements = 15), with conventional (n = 6, m = 7), and additional clam-shell shielding (n = 33, m = 58). The corresponding median values were 2.1% (SD 1.07), 1.7% (SD 0.28) and 1% (SD 0.41) of midplane dose (Table 1, Figure 1). According to direct comparisons, a dose reduction of about half can be expected in most cases (Figure 2). Mean dose fluctuations of 11.6% (median 10%) have to be taken into account.

Conclusion: Effective shielding can diminish gonadal dose in seminoma patients to about 1% of midplane and gives a good possibility of taking the maintenance of fertility and the desire to have children into account (Table 2). The application should be considered especially for patients with impaired spermatogenesis before RT. Eventual fluctuations induced us to determine the gonadal dose 3 times per patient in direct measurements (Table 3).