Image Guided Radiation Therapy (IGRT)
IGRT involves any use of imaging data to aid in decisions of the radiotherapy process, decision of whether/how to treat, delineation of structures of interest, aid in positioning, verification, and monitoring, assessment and prognosis of outcome. It may be ultrasound, planar x-ray or volumetric based imaging.
Tumours can move between treatment sessions due changes in organ filling or while breathing. There could also be variations in patient’s position during day-to-day treatment session set up. Since, the radiation dose was more and more confined to the tumour.
Naturally, there developed a need to see the location of the tumour during the delivery treatment sessions. Until now the Radiation Oncologists have been treating patients with External Beam Radiation Therapy in a mathematically precise way but unable to see what is being treated. Now, a new technology has arrived to overcome this defect. The change in the position of tumour can be tracked with a CT image, just before the treatment delivery and the appropriate corrections are made online. The imaging information from the “planned CT” scan done earlier is overlapped on this CT. This alignment helps doctors to correct the position of the patient. This is called IGRT (Image Guided Radiotherapy). IGRT further helps to better the delivery of radiation.
Which tumours benefit from IGRT treatment?
In the era of high precision radiotherapy, practically all tumour sites requires IGRT treatment, especially Head and Neck tumour, tumours which move with respiration like lung tumours, pelvic tumour.
The improved dose conformity and steep dose gradients like Intensity Modulated Radiation Therapy (IMRT) necessitate enhanced precision and accuracy in patient localization and spawn the development of IGRT, in which various metabolic and anatomical imaging techniques are integrated into the radiation therapy process. The overall goal of IGRT is to target tumours more accurately while better sparing the normal tissues. Much recent effort is focused on removing the uncertainty in the definition of the target volume and in the determination of the position of mobile and then deformable organs.