Divergent blocks are used with photon beams to reduce what specific aspect?

Divergent blocks are specifically designed to reduce the transmission penumbra when used with photon beams. The penumbra refers to the area at the edges of the radiation beam where the dose falls off from the full radiation intensity to zero. In radiotherapy, minimizing penumbra is crucial because a smaller penumbra results in more precise dose delivery to the tumor while reducing exposure to surrounding healthy tissues.

By using divergent blocks, which are essentially shaped to conform to the beam’s divergence, the treatment planner can effectively manage the beam’s profile as it exits the treatment head and interacts with the patient. This limits the width of the penumbra zone, ensuring that high doses are delivered to the target area with minimal spillover to nearby normal tissues. Proper management of the penumbra is important for enhancing the effectiveness of the treatment and minimizing side effects.

The other options deal with different aspects of radiation delivery. Depth of the beam pertains to how far the radiation penetrates tissues. Scattered radiation refers to radiation that has been redirected by interaction with matter, which can complicate dose calculations. Beam hardening involves the preferential absorption of lower-energy photons in the beam, altering the energy spectrum of the radiation; however, none of these directly relate to the