OBJECTIVES: I. Compare relapse rates in patients with stage I testicular seminoma treated with adjuvant radiotherapy vs carboplatin. II. Compare quality of life of patients before and after treatment with these regimens. III. Compare the acute and intermediate (1-2 year) side effects of these regimens in these patients. IV. Determine the incidence of late side effects (such as bowel dysfunction) of treatment and second malignancies in these patients.

OUTLINE: This is a randomized study. Patients are randomized to 1 of 2 treatment arms. Arm I: Patients receive a single dose of carboplatin IV. Arm II: Patients undergo radiotherapy once daily, 5 days a week. Patients are followed every 3 months for 1 year, every 4 months for 1 year, every 6 months for 1 year, and then annually thereafter.

PROJECTED ACCRUAL: Approximately 800 patients will be accrued for this study within 4 years.

DISEASE CHARACTERISTICS: Histologically confirmed stage I seminomatous germ cell tumor of the testis categorized as either "classical" or "anaplastic"

PATIENT CHARACTERISTICS: Age: 16 and over Performance status: Not specified Hematopoietic: Not specified Hepatic: Not specified Renal: Creatinine less than 1.4 mg/dL Other: No concurrent or previously treated malignancy except successfully treated nonmelanoma skin cancer No medical condition or other factor that would preclude study

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: Not specified Endocrine therapy: Not specified Radiotherapy: Not specified Surgery: No more than 8 weeks since prior orchidectomy Prior inguino-pelvic or scrotal surgery allowed Must be treated with "dog-leg" field if randomized to radiotherapy If prior vasectomy, choice of fields is at the discretion of the clinician