Intensity Modulated Radiation Therapy
Advances in a clinical field like radiation oncology may emphasize either improvements in tumor control or decreases in normal tissue side effects, or both. For decades, radiation oncologists attempted to increase tumor control by expanding the treatment fields and including more and more tissue in the irradiated area. More recently, however, an alternative localized treatment philosophy emphasizing much more restricted treatment fields has been evaluated. For very small clinical targets, a treatment technique such as stereotactic radiosurgery or high dose rate brachytherapy may be appropriate and more effective than intensity modulated radiotherapy.
However, these very focal procedures are not well-suited to larger anatomic targets. For these larger targets, clinicians and physicists have been working to develop ways to sculpt the dose distributions to match target site geometry, thus sparing virtually all surrounding normal tissues. This has been impossible in the past because treatment fields were designed to be highly uniform, resulting in relatively large treatment volumes.
The newer "dose-painting" techniques give much less emphasis to dosimetric uniformity and much more emphasis to a careful match between the intensity of treatment and the perceived tumor risk in each area. By "modulating" treatment beams and by dividing anatomic targets into a large number of connected sub-targets (each of which may be targeted individually) a much better match between the deposited radiation and the anatomic tumor location may be achieved. This approach is called "intensity modulated radiation therapy" or IMRT.
The Intensity Modulated Radiotherapy Programs
At Cleveland Clinic, several different intensity modulated radiation therapy programs are in practice. For these intensity modulated radiotherapy programs, the early clinical results suggest that intensity modulated radiation therapy treatment effectiveness is at least as good as those achieved using the older techniques, and normal tissue sparing is substantially better. Several more years of follow-up data will be required before specific tumor control statistics can be published for intensity modulated radiation therapy. Nevertheless, we are convinced that intensity modulated radiation therapy represents a major evolutionary step in radiosurgery technology progress as seen in clinical radiation medicine.
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