**Core Concept**
Intracavity brachytherapy followed by external beam radiotherapy is a standard treatment approach for cervical cancer (Ca Cervix) stage IIIB, which is a locally advanced disease. This multimodal treatment strategy involves delivering high doses of radiation directly to the tumor site while minimizing damage to surrounding healthy tissues.

**Why the Correct Answer is Right**
Intracavity brachytherapy involves the placement of radioactive sources inside the cervix to deliver high doses of radiation directly to the tumor. This is followed by external beam radiotherapy, which targets the tumor from outside the body. The combination of these two modalities allows for the delivery of high doses of radiation to the tumor while minimizing damage to surrounding tissues. The use of brachytherapy in this context helps to optimize the local control of the tumor, while external beam radiotherapy provides additional coverage of the tumor and surrounding lymph nodes.

**Why Each Wrong Option is Incorrect**
**Option A:** Wertheim's hysterectomy is a surgical procedure that involves the removal of the uterus, cervix, and part of the vagina. While it may be an appropriate treatment for early-stage cervical cancer, it is not typically used for stage IIIB disease due to the extent of the tumor and the potential for lymph node involvement.

**Option B:** Schauta's hysterectomy is a type of radical abdominal hysterectomy that involves the removal of the uterus, cervix, and part of the vagina. Like Wertheim's hysterectomy, it is not typically used for stage IIIB disease due to the extent of the tumor and the potential for lymph node involvement.

**Option C:** Chemotherapy may be used as part of the treatment for cervical cancer, particularly in the neoadjuvant setting or as part of a chemoradiation regimen. However, it is not typically used as the sole treatment for stage IIIB disease.

**Clinical Pearl / High-Yield Fact**
When treating cervical cancer, it's essential to consider the stage and extent of the disease when selecting a treatment approach. In general, early-stage disease may be treated with surgery or radiation therapy, while more advanced disease may require a combination of chemotherapy, radiation therapy, and surgery.

**✓ Correct Answer: D. Intracavity brachytherapy followed by external beam radiotherapy**