CT simulation is a foundational step in preparing for radiation therapy. This procedure uses specialized computed tomography (CT) imaging to create a detailed three-dimensional map of a patient’s internal anatomy. The information gathered during this initial session forms the basis for designing a precise and individualized radiation treatment plan.
Why CT Simulation is Essential for Radiation Therapy
CT simulation plays a central role in modern radiation therapy because it enables highly accurate treatment delivery. Unlike a diagnostic CT scan, which is primarily for identifying disease, the simulation CT focuses on mapping the tumor’s exact location and its relationship to surrounding healthy tissues and organs. This detailed mapping allows the radiation oncology team to effectively target cancerous cells while minimizing radiation exposure to nearby healthy structures, thereby reducing potential side effects and protecting sensitive organs. This tailored approach ensures that the prescribed radiation dose is delivered accurately to the target, maximizing treatment effectiveness and patient outcomes.
The CT Simulation Procedure
The main objective of a CT simulation appointment is to ensure the patient is positioned exactly as they will be for each daily radiation treatment. To achieve this consistent positioning, various immobilization devices may be used, such as custom-molded masks for head and neck treatments, vacuum bags that conform to the body, or specialized boards and cushions.
Once positioned on the CT scanner’s flat table, therapists use laser lights to align the patient’s body precisely. A scout scan, a quick preliminary image, helps confirm the patient’s straightness before the full CT scan begins. During the scan, the table moves through the large CT bore, and the patient’s main role is to remain still.
Following the scan, the radiation oncologist reviews the images to define the treatment area. Small, permanent tattoos, often resembling freckles, may be placed on the skin to serve as external reference points for daily treatment alignment. Alternatively, temporary ink marks or specialized skin markers can be used for the same purpose.
From Simulation to Treatment Planning
After the CT simulation scan is complete, the acquired images are transferred to a specialized treatment planning system. Radiation oncologists and medical dosimetrists then collaborate to delineate the exact boundaries of the tumor, known as the target volume, and identify nearby healthy organs that need to be avoided, referred to as organs at risk.
This detailed outlining process allows the team to create a virtual simulation of the radiation treatment. Using sophisticated software, they design the radiation beam arrangements, angles, and energies to deliver the prescribed dose to the tumor while sparing healthy tissues.
The treatment planning system calculates how the radiation will interact with different tissue densities, ensuring accurate dose delivery. The plan is then reviewed by the radiation oncology team for quality assurance before the patient’s radiation treatments can begin.