The external testicular shield used when treating seminoma is intended to protect the remaining testicle from:

The external testicular shield is designed to protect the remaining testicle from internal scatter radiation during the treatment of seminomas. During radiation therapy, the primary beam is directed at the tumor, but some radiation can scatter within the treatment area and affect surrounding tissues. Without a shield, the remaining testicle can receive unintended radiation exposure that may compromise its function or health.

The shield's primary purpose is to minimize this scatter radiation impact while still ensuring that the seminoma receives the adequate therapeutic dose it requires for effective treatment.

While protecting against the primary beam is also a consideration during treatment planning, the shield specifically addresses the challenge of scatter, which can inadvertently expose non-target tissues. The other options, such as radioactivity or contamination from hands, do not pertain to the purpose of a testicular shield in this context, as they relate more to concerns about radioactive materials or safety practices rather than minimizing scatter radiation within the treatment area.