WHAT IS IGRT/IMRT?
IGRT/IMRT is our contemporary method of treating patients with radiation therapy. IGRT/IMRT is one of the most technologically advanced treatments available in external beam radiation therapy. By allowing your physician to treat cancers with more accuracy than ever before possible, the cure rates of certain cancers can be increased while decreasing the side effects of treatment at the same time. It is the single biggest improvement in radiation therapy in the last 50 years.
IGRT/IMRT OFFERS HIGHER CURE RATES WITH LESS SIDE EFFECTS
In the early days, simple low-energy x-rays were found to be very effective for treating superficial skin cancers. Higher energy machines and then Cobalt were developed that could treat deeper cancers. However, these early machines often gave a higher dose to the skin than the tumor, limiting cure rates. Fifty years ago, linear accelerators, which accelerate electrons near the speed of light to generate even higher energy x-rays, were developed. These machines concentrate the dose internally, with much sharper edges and as a result, have allowed treatment to far higher doses while staying below the tolerance of surrounding normal tissues. This has resulted in far higher cure rates for many cancers that we see today.
In order for us to continue to cure more people who develop cancer, we have to give much higher doses of radiation than originally thought, in order to kill every remaining cancer cell. At the same time, it is imperative to stay within the tolerance of the surrounding normal tissues, or else unacceptable side effects may result. IGRT/IMRT allows us to accomplish exactly that, resulting in higher cure rates, decreased side effects, or both.
IGRT/IMRT is a highly specialized conformal radiation treatment technique that conforms a high dose radiation beam to a defined target, such as a tumor, while restricting dose to the surrounding sensitive structures. Essentially, this technology “3D prints” the high dose volume around the target, with small margins, whereas older radiotherapy techniques were not nearly this precise.
IGRT/IMRT TREATMENT PROCESS
First, the treatment planning is performed in an entirely new way versus historical techniques. IGRT/IMRT uses inverse planning, whereby the computer is told “Give enough dose to completely kill the tumor while staying within tolerance of the spinal cord and kidney.” The computer will then create thousands of field combinations and produce the one that does the job best. While it takes the computer 8-40 hours to do each plan, it would take a human ten times that amount to do a job which would still not be as good as what the computer can do! Over the years, it has been found that increasing the dose of radiation is the single best way to increase cure rates from cancer, and this new generation of IGRT/IMRT devices allows us to do just that, without any increased risk of damage to adjacent normal tissues
The process of treating a patient with IGRT/IMRT is a very elaborate one. First, the patient is immobilized in a position which is comfortable. Sometimes, this may involve the manufacture of a custom device such as a plastic mask or a formed mold. The patient is then scanned in the treatment position on a dedicated high-speed CT scanner. The images are then downloaded to a very sophisticated treatment-planning computer. The attending physician then outlines the tumor, its possible microscopic extensions, any lymph nodes in the area which may be involved, and all normal structures in the area to which dose must be monitored. In the head and neck area, this can involve outlining 12-14 separate structures on each CT slice, which are spaced at 2.5 mm intervals. When necessary, other imaging studies, such as MRI scans or Positron Emission Tomography (PET) scans can be “fused” with the planning CT images in order to more accurately define the tumor, its extensions, and normal tissues.
Dedicated medical physicists then begin their work to produce a plan to actually treat the patient. The physicist and certified dosimetrist work with the radiation oncologist much as an anesthesiologist works with a surgeon – just as it’s not possible to perform great surgery without a top-notch anesthesiologist, it’s not possible to do great radiation therapy without a top-notch physicist, and the physicists at Unio Specialty Care are as good as they come. The physicist and/or dosimetrist directs the computer to begin the planning process, and then monitors progress. Many adjustments are often necessary in order to produce a plan which will be the best to treat a patient. The physician and physicist then meet and review the plan together, reviewing carefully the dose to the tumor and each surrounding organ CT slice by CT slice, to ensure that the plan is the absolute best one for the individual patient.
Before the patient is actually given their first dose of radiation, two more important steps must be completed. First, a mannequin which has the same density as the human body is placed on the treatment table and treated in the exact same manner as the patient will be. By use of complex dosimetry analysis using both film and diodes, the dose to each area is calculated precisely as a second check. Then, the patient is brought in and films are taken which are compared to digitally-reconstructed radiographs that the computer generates. Only after both of these second checks have been completed is the ok given to actually treat the patient.
IGRT/IMRT has been shown to be particularly useful for cancers of the prostate, lung, GI tract and head and neck region. Other sites which show potential benefit include the breast, pelvis, and any tumor wrapping itself around critical organs or tissues. It represents the single largest technical enhancement in the history of therapeutic radiation and has become the de facto standard of care for many, if not most cancer lesions, treated with curative intent.