Generally, radiotherapy should not be used for treating benign conditions. The only possible exception being:

Ans. B. Extensive pigmented villonodular synovitisPVNS is commonly seen around knee. Synovial inflammation occurs due to cholesterol and pigment deposition. Radiotherapy may alleviate this disease. Else one has to go with synovectomy. Malignant transformation is reported but very rare.SYNOVIAL SARCOMA is a soft tissue tumor that does not have synovial origin despite its name. It is a rare but aggressive tumor that arises from tendon sheaths or joint capsules where there are multipotent stem cell rests that differentiate into mesenchymal as well as epithelial structures, hence a BIPHASIC TUMOR. It is characterized by Ctrl (X;18). Excision is the treatment of choice.