Intensity Modulated Radiation Therapy (IMRT) gives the physician a powerful tool that utilizes state of the art technology to deliver doses of radiation with intensity and accuracy that were previously unachievable. These advances allow the team of physicians, physicists, dosimetrists and therapists to maximize the dose of radiation to the tumor while sparing the healthy tissue surrounding the cancer. IMRT technology is so advanced that the treatment machine can be programmed to “wrap” the radiation around the tumor while giving neighboring structures much lower doses.
IMRT is being used to increase tumor control and decrease toxicity in body sites such as the brain, head & neck, lung, esophagus, spine, pancreas, liver, bladder and prostate. IMRT is also very useful in treating areas that have already received significant doses of conventional radiation therapy.
The benefits of IMRT include higher daily doses that can control disease more effectively, fewer side effects due to lower doses to normal tissue, and a reduced number of treatments. These combine to allow the patient to maintain strength and lead more normal lifestyles during the course of treatment while increasing the potential for cure.
IMRT utilizes the technology to provide a highly customized treatment that satisfies the prescription better than 3D Conformal RT. In 3DCRT, the dose within the treatment volume is fairly homogeneous, usually +/- 3-5%. With IMRT, the computer can create a plan that has a much more varied dose distribution and can actually focus the hot spots in areas that are chosen by the physician.
The advances in technology that have brought the Multi-Leaf Collimator (MLC) and record and verify to the clinical setting have allowed the advances seen in IMRT. In coordination with the treatment planning computer, the record and verify software drives the treatment machine through the sequence of fields established in the plan. Each IMRT treatment portal actually consists of many individual fields, called beamlets, which are defined by specific MLC settings. IMRT plans generally consist of 3-6 beams, but it is not uncommon to treat with 8, 9 or more each day, depending on the tumor location and the associated limiting structures. Because the dose distribution can be tailored to meet specific criteria set by the physician for both target volumes and critical structures, it is possible to deliver higher daily doses than with 3DCRT while keeping the incidence of side effects at comparable levels.
This is arguably the greatest advantage of IMRT over 3DCRT because higher daily doses will allow the patient to complete treatment sooner than traditional dose schedules.