The position of the patient is carried out using a special chair together with a mask that, in the case of a brain tumor, immobilizes the head. Location with respect to the beam is carried out first using an X-ray machine to delineate the tumor and then using laser beams for relocation during the succeeding treatment. The patient is monitored with audio and visual links. All aspects of treatment are regulated by computer control.
Proton radiation therapy has several important advantages over conventional techniques-those common in hospitals-that use photons (X rays). The major advantages come from the totally different manner by which protons and photons lose energy in matter. These differences are best appreciated by referring to figure 2 below.
Two advantages are readily apparent. (1) For a fixed dose at the tumor, protons give an appreciably lower dose to healthy tissue in front of the tumor. (2) The sharp cut-off of the proton radiation field ensures that healthy tissue beyond the tumor is not affected. In addition, the lateral edges of the radiation field are also much better defined when using protons. These advantages have been known for some time, but the cost of building proton facilities from scratch has been a major limiting factor.
The availability of energetic protons in precisely defined beams at IUCF led to the formation in 1990 of a collaboration to explore using them for therapy. The 200-MeV protons are well suited for therapy, since they will penetrate up to 10 inches of tissue. The program started with experiments to understand exactly the effectiveness of protons relative to photon radiation in killing cancerous cells. Many calibrations were also necessary. Hardware was designed, developed, and constructed to carry out simple procedures with patients seated in a special chair. The first patient, who had a deep-lying brain tumor, was successfully treated in fall 1993. A CT (computer tomography) scan showing a lateral cut through the head is compared with the radiation treatment plan (see figure 3). The patient was treated using beam from three different directions. These three beams intersected at the tumor, which therefore received a much greater dose than did the surrounding tissue, as shown by the curves on the treatment plan that correspond to different total dose levels. Close to the peak, the dose to the healthy tissue-compared with the dose for the cancer tumor-is reduced to 50 percent at a distance of a quarter inch away. Final approval from the Federal Drug Administration to permit treatment of control groups of patients is expected soon.
The Indiana University facility will be the third in the country to use protons for therapy. Other centers are operating at teh Harvard and Loma Linda medical centers. Protons have several other medical applications, and already, studies are under way to exploit further the capabilities available at the Indiana University Cyclotron Facility.
Funding for the Proton therapy Area was provided by the Lions Club of Indiana, The Little Red Door (Marion County Cancer Society, Inc.), and Indiana University.