Advancements in Image-Guided Radiation Therapy (IGRT)

After X-rays were discovered by Wilhelm Conrad Röntgen in 1985, their use in clinics as a cancer treatment tool was rapid. With the developments in the field of CT and the use of CT in treatment planning, 3D conformal radiotherapy has been introduced, in which three-dimensional tumors can be created, normal tissues can be drawn, and dose distributions can be calculated. In the 1990s, intensity-modulated radiotherapy (IMRT), began to be used. Compared to conformal radiation therapy, IMRT is more flexible in controlling beam fields, has better dose distribution, and has fewer side effects. Arc therapy appeared as a response to the limitations in fixed areas. Arc therapy has some advantages over IMRT. The desire to see the target volume during the treatment process led to the development of IGRT, which provides optimal targeting of the desired organs and limits them to critical organs. On-board systems refer to imaging devices connected to the radiotherapy device. The most commonly used on-board system is EPID. Clinical application of IGRT for verification and correction of the patient’s position can generally be done offline or online. The first monitors the patient’s position between fractions and reviews safety margins and/or plan accordingly. This is also known as adaptive radiation therapy (ART). Many geometric errors can be corrected online. Image-guided radiation therapy (IGRTx) that uses X-ray-based technology, which combines a kilovoltage X-ray source and a flat-panel imager with treatment devices, has been used for years, but despite its success, two inherent limitations to IGRTx have emerged. Magnetic resonance-guided radiation therapy (MRgRT) combines the magnetic resonance system with a radiotherapy device, allowing real-time imaging of the target volume and critical organs before and during treatment and renewing the plan when necessary. Recently, the use of surface-guided radiation therapy with optical surface scanning, intra-fraction movements, and breath tracking systems has increased in clinics. SGRT systems use a projector system and several camera systems to perform real-time, three-dimensional surface scanning of the patient.