Brachytherapy sources used in interstitial therapy are typically in the form of which options?

In interstitial therapy, brachytherapy sources are primarily delivered directly into or very close to the tumor. These sources can take several forms, and the most common include needles, wires, ribbons, and seeds. Each of these forms allows for precise placement and targeting of the radiation to the tumor while minimizing exposure to surrounding healthy tissue.

Needles are often used for delivering radioactive sources into the tumor, especially for temporary implants, while wires and ribbons can be used for more complex geometries or when a series of sources need to be placed in a specific manner. Seeds are typically small, encapsulated sources placed permanently or temporarily, depending on the treatment plan. This flexibility in using multiple forms of sources is crucial for tailored treatments that match the specific characteristics of the tumor being treated.

Other options like liquid solutions and powdered forms are not generally used in interstitial therapy. Liquid radioactive sources are more common in different applications, such as injected therapies, while powdered forms may not provide the necessary containment and precision required for effective interstitial brachytherapy. Therefore, the diversity of delivery methods represented in the correct answer reflects the versatility and precision necessary for effective treatment in this field.