Which of the following radioisotopes is sometimes administered into the peritoneal cavity in the treatment of gynecological malignancies?

Phosphorus-32 is often administered into the peritoneal cavity for the treatment of gynecological malignancies. This radioisotope is a beta-emitting radionuclide that can effectively target malignant cells. When introduced into the peritoneal space, it takes advantage of localized tumor effects and minimizes radiation exposure to surrounding healthy tissues. The peritoneal cavity is a common site for the spread of gynecological cancers, making the use of phosphorus-32 particularly appropriate.

In contrast, the other options are not typically used in this manner for gynecological treatments. Cesium-137 and iridium-192 are used in brachytherapy, primarily for solid tumors and involve different administration routes. Iodine-131 is mainly utilized for thyroid-related conditions and does not have a significant role in the treatment of gynecological cancers through intraperitoneal administration. Thus, phosphorus-32 is more suitable for treating this specific type of cancer by delivering localized radiation effectively.