Telecobalt machines can provide field sizes (at SAD) in the range of about:

Telecobalt machines are used in radiation therapy to deliver cobalt-60 gamma radiation. The field sizes at a specified source-to-axis distance (SAD) are a critical parameter for treatment planning as they determine the area of tissue being irradiated. The typical field size for telecobalt machines ranges from 5 cm x 5 cm to 40 cm x 40 cm, which allows for effective treatment of various tumor sizes and shapes.

The capability to provide a range of field sizes is essential for tailoring the radiation dose to the specific dimensions of the tumor while minimizing exposure to surrounding healthy tissues. The range of 5 cm x 5 cm to 40 cm x 40 cm reflects the flexibility and practicality that telecobalt units offer in clinical settings.

Other options list field sizes that are either too small or too large for standard telecobalt operations. For instance, a range that starts at 1 cm x 1 cm would be too limited for typical therapeutic uses, while an upper limit of 50 cm x 50 cm exceeds the usual operational capacity of these machines. Thus, the answer reflects the correct and practical operational limits of telecobalt machines in radiation therapy.