Intensity Modulated Radiation Therapy (IMRT)
IMRT involves using hundreds of tiny radiation beam-shaping devices, called collimators to impart a single dose of radiation. Collimators may be mobile or stationery during the treatment so that intensity of the radiation beam can be modulated as required. Dose modulation permits different areas of the tumor or nearby tissues to receive the different dosage.
IMRT is planned in inverse also known as inverse treatment planning. In this treatment the radiation dose is chosen for different areas of the tumor and surrounding tissue and then a high powered computer program is used to calculate the required number of beams and angles for the radiation treatment. In traditional (forward) treatment , the number and angles of radiation beams are assessed in advance and the computer calculates the dosage that would be delivered from the planned beams.
The objective of using IMRT is to raise the radiation dose to areas which require it more and at the same time reduce the radition exposure of the normal surrounding tissues. IMRT reduces the risk of side effects in contrast to 3D-CRT. Some common side effects associated with 3D-CRT are damage to the salivary glands resulting in dry mouth or xerostomia. This happens during radiation therapy used on head and neck. IMRT results in exposure to radiation for even normal tissues. It is not known whether IMRT can lead to better control of tumor growth in comparison to 3D-CRT.
Image-guided radiation therapy (IGRT)
IGRT involves repeated imaging scans (CT, MRI or PET) are carried out. The imaging scans are computer processed and changes are observed in the tumor size and location due to the treatment so that the position of the patient or the planned radiation dose can be modified during treatment as and when required.
The accuracy of radiation treatment is enhanced through repeated imaging and permit reduction in the planned volume of tissue that is to be treated. Thus normal tissue’s exposure to radiation is reduced.