Biomedical Imaging and Radiotherapy:
Intenisty Modulated Radiotherapy Treatment Planning
A Powerful Approach for Cancer Treatment
Intensity modulated radiation therapy (IMRT) is a recently developed and highly effective method for destroying cancerous tumors with minimal side effects to the patient. The idea behind IMRT is to deliver a lethal radiation dose to the tumor using multiple beams coming from different angles. The beam shapes and orientations are chosen to maximize the irradiation of the tumor while minimizing the irradiation of healthy tissues and organs at risk.
Spectral Sciences Inc. is developing novel algorithms and software to assist in IMRT radiotherapy treatment planning and radiosurgery in collaboration with RAHD Systems, a leader in radiation therapy software, and with research support from the National Institutes of Health. In the past, finding the best beam placements and shapes (modulation patterns) typically required extensive trial and error simulations guided by an expert physician and/or physicist. Such a method does not guarantee satisfactory results, especially for unusual tumors with which the physician may have little or no prior experience.
In contrast to the trial-and-error approach, SSI's algorithms predict the optimum beam placement and modulation patterns from first principles. Optimum beam configurations are chosen from the options of coplanar, non-coplanar, stereotactic, and dynamic arc therapies with user-defined beam intensity modulation. These include beam delivery with dynamic and static multileaf collimators and wedges for intensity modulation or beam shaping. The algorithms incorporate data from calibrated water phantom measurements for accurate beam optimization and dose prediction.
Parties interested in possible collaborative development in this area should contact Dr. Robert Levine at bob(at)spectral.com or tel. (781) 273-4770. Some examples of our computed IMRT radiation dose plans are shown below.
Examples:
The following figure shows the calculated radiation dose delivered to a rear-brain tumor using an IMRT plan generated by one of our algorithms. The dose contours are shown superimposed on a CT image. The delivered dose contours are seen to conform very well to the tumor volume while avoiding the brainstem and sensitive tissues.
The calculated dose map for an IMRT treatment for prostate cancer is shown below. Using a new, 3D IMRT model we have shown that non-coplanar IMRT treatments further reduce the dose to the rectum and bladder compared to coplanar treatments.
The following two figures depict IMRT treatments for breast cancer in which beam resolution effects are computed. It is seen that the use of higher resolution beam collimators (right) can reduce radiation dosage to the surrounding tissue.
The next example illustrates the impact of higher-order (such as tissue density-related) dose effects in IMRT planning for a brain stem tumor. The radiation plan and dose map were computed taking into account the effects of the sinus air cavities on the radiation scattering and attenuation. The delivered dose contours on the right show that there is no dose deposition in the sinuses. Because higher-order dose effects are incorporated in the inversion to beam orientation and modulation, the delivered dose is concentrated on the tumor even for treatment through highly non-homogeneous tissues.
