What is the purpose of the TV in radiation therapy?

The purpose of the treatment volume (TV) in radiation therapy is primarily to delineate a specified isodose surface. In radiation therapy, isodose surfaces represent areas where the dose delivered is equal, which is crucial for ensuring that the prescribed dose is accurately administered to the target tissue while sparing surrounding healthy tissues.

By defining these isodose surfaces, medical professionals can effectively target the tumor while minimizing exposure to adjacent normal structures, which is essential for maximizing treatment efficacy and reducing side effects. This is particularly important in complex cases where tumors may be located near critical organs or structures.

The other choices, while related to aspects of therapy and planning, do not specifically address the primary role of the treatment volume in conjunction with isodose distributions. The TV focuses clearly on ensuring optimal dose distribution, which is vital for the success of radiation therapy.