How does the output of a 60 Cobalt unit, when measured in a phantom, compare to the measurement in air at the same point?

The output of a 60 Cobalt unit, when measured in a phantom, is typically less than the measurement taken in air at the same point due to several key concepts in radiation physics.

In air, the measurement reflects the dose delivered by the radiation in a medium with lower density and atomic composition compared to tissue-like materials in a phantom. When measuring in a phantom, which is designed to simulate human tissue, the radiation interacts more with the material, resulting in attenuation and scattering effects that are not present to the same extent in air. This leads to a reduction in the intensity of the measurable radiation dose, resulting in lower readings.

The difference between measurements in air and a phantom is crucial for accurate dosimetry, especially in treatment planning and verification processes in radiation therapy. Knowing that the output is less in a phantom helps dosimetrists make necessary adjustments to ensure that the prescribed dose to the actual patient aligns correctly with what is delivered in practice. This concept is fundamental in the field of medical dosimetry to ensure safety and effectiveness in treatment delivery.