For accurate planning and dose delivery, what must be identical during CT, simulation, and treatment?

In the context of ensuring accurate planning and dose delivery in radiation therapy, it is essential that the patient support assembly or couch top is identical during the CT scan, simulation, and actual treatment phases. Consistency in the positioning of the patient is critical to achieving accurate targeting of the tumor while minimizing exposure to surrounding healthy tissues.

When the same couch top or support assembly is used throughout these steps, it helps to replicate the patient's positioning in a standardized manner. This consistency reduces variability and enhances the precision of the treatment plan, ensuring that the dose calculated during the simulation matches the dose delivered during treatment. If the patient is positioned differently, even marginally, it could lead to discrepancies in the target volume coverage and increase the risk of underdosing the tumor or overdosing healthy tissue.

Other aspects, such as imaging technique, may vary due to advancements in technology or different settings, and while patient demographics are important for overall treatment planning, they do not directly influence the delivery process as the couch top does. Radiation dose type is also a key element in treatment planning but is not something that needs to remain identical across the three phases being discussed. Therefore, the patient support assembly or couch top is fundamental for accurate positional consistency throughout the treatment delivery process.