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Radiation Therapy Simulator

Radiation therapy is a medical specialty for treatment of malignancies (tumors or neoplasms) with high doses of radiation using X rays, γ rays, electrons, protons, and neutrons. This field is rapidly evolving because of recent advances in the technology used for diagnosis, treatment planning, treatment delivery, and verification of patient treatments. One of the cornerstones of modern radiation therapy practice are volumetric patient image datasets from computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), and ultrasound (US). Devices that produce the primary images for use in radiation therapy treatment planning are called Radiation Therapy Simulators. Current devices include (1) Conventional Simulators (based on conventional X-ray radiography planar imaging); (2) CT-simulators (based on CT scanners); (3) PET/CT-simulators (based on PET/CT scanners); (4) MR-simulators (based on MR scanners). 
 
 
 
The radiation therapy simulator has been an integral component of the treatment planning process since the 1960s. Conventional simulators are designed to mimic the linear accelerator geometry while providing a diagnostic-quality X-ray beam for anatomic imaging. Because of the increased use of three-dimensional (3D) imaging for treatment planning, conventional simulators are less popular than in the past. Still, this technology continues to be developed and retains its presence in most radiation oncology departments. Shortly after the introduction of clinical CT scanners in the early 1970s, it was realized that this imaging modality had much to offer in a radiation oncology setting because they provided a volumetric view of the patient’s normal and tumor anatomy with excellent spatial accuracy. In response, CT simulators were developed during the 1980s, and 1990s and today CT simulator is the main imaging device in radiation therapy. The CT simulators have developed to a point where CT scanner manufacturers are designing scanners specifically for CT simulation purposes. PET imaging can also provide valuable information about tumors and PET–CT scanners have been implemented as radiation therapy simulators and can be found in many radiotherapy centers. Finally, MRI scanners have also been implemented and are used for treatment simulation in radiation therapy. The MRI scanners are less commonly found in radiotherapy departments, but because of the imaging advantages that MRI has to offer it is expected that the use of MRI scanner for radiotherapy simulation will experience significant growth. 
 
 
 
This article describes the radiation therapy simulation process, design and features of conventional, CT, PET–CT, and MRI simulators, and their use for treatment planning. 
 
 
Keywords: 
 
radiation therapy; 
radiotherapy; 
brachytherapy; 
simulators; 
CT; 
MRI; 
PET; 
X rays; 
cancer, imaging; 
image guidance