Purpose: To investigate radiation doses to the testes delivered by a radiolabeled anti-CD20 antibody and its effects on male sex hormone levels.
Materials and methods: Testicular uptake and retention of 131I-tositumomab were measured, and testicular absorbed doses were calculated for 67 male patients (54±11 years of age) with non-Hodgkin’s lymphoma who had undergone myeloablative radioimmunotherapy (RIT) using 131I-tositumomab. Time–activity curves for the major organs, testes, and whole body were generated from planar imaging studies. In a subset of patients, male sex hormones were measured before and 1 year after the therapy.
Results: The absorbed dose to the testes showed considerable variability (range=4.4–70.2 Gy). Pretherapy levels of total testosterone were below the lower limit of the reference range, and post-therapy evaluation demonstrated further reduction [4.6±1.8 nmol/l (pre-RIT) vs. 3.8±2.9 nmol/l (post-RIT), P<0.05]. Patients receiving higher radiation doses to the testes (≥25 Gy) showed a greater reduction [4.7±1.6 nmol/l (pre-RIT) vs. 3.3±2.7 nmol/l (post-RIT), P<0.05] compared with patients receiving lower doses (<25 Gy), who showed no significant change in total testosterone levels.
Conclusion: The testicular radiation absorbed dose varied highly among individual patients. Patients receiving higher doses to the testes were more likely to show post-RIT suppression of testosterone levels.