The geometric penumbra of a 60 Co unit depends on which of the following factors?

Prepare for the Medical Dosimetry Certification Test with comprehensive flashcards and multiple choice questions, complete with hints and explanations. Ensure your success by studying key topics covered in the exam!

The geometric penumbra is a crucial concept in radiation therapy that refers to the gradual transition from full radiation dose to no radiation dose at the edges of the treatment field. It is influenced by several geometric factors related to the radiation source and its positioning.

When considering the factors that affect the geometric penumbra of a cobalt-60 (60 Co) unit, the combination of source diameter and source to diaphragm distance is particularly significant. The source diameter represents the size of the radioactive source, which directly impacts the sharpness of the radiation beam. A larger source leads to a wider penumbra, as the rays emitted from different point positions around the source create a more significant spread in dose distribution at the boundaries of the treatment area.

Additionally, the distance from the source to the diaphragm is also critical. The diaphragm is used to shape and limit the treatment field. As the distance from the source to the diaphragm increases, the penumbra becomes wider due to the divergence of the radiation beam. This results in a less concentrated dose at the edges of the treated area.

Therefore, the geometric penumbra is determined by both source diameter and source to diaphragm distance, making this choice the correct answer. Understanding these relationships is vital for dosimetrists to

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