What aspect does the immobility during treatment primarily reduce?

Immobility during treatment primarily reduces the likelihood of setup errors. When a patient remains still throughout the radiation therapy procedure, it ensures that the treatment is delivered consistently and accurately to the intended area. Variations in patient position can lead to discrepancies in the treatment field, which can affect the amount and distribution of radiation delivered. This is crucial because radiation is precisely targeted to kill cancer cells while minimizing damage to surrounding healthy tissues. Maintaining a stable position helps in maintaining the accuracy of the treatment plan, which is essential for effective patient care.

While immobility might also have implications for the patient's comfort and pain levels, it does primarily focus on ensuring that the treatment setup remains as intended, thereby significantly reducing the chance of errors in targeting the tumor. Hence, while other elements may be influenced by patient position, the primary purpose of ensuring patient immobility is to minimize setup errors.