Present Status and Future Developments in Proton Therapy

Within the past few years, interest in proton therapy has significantly increased. This interest has been generated by a number of factors including: 1) the reporting of positive clinical results using proton beams; 2) approval of reimbursement for delivery of proton therapy; 3) the success of hospital-based proton therapy centers; and 4) the availability of modern, integrated proton therapy technology for hospital-based facilities. In the United States, this increased interest has occurred particularly at the level of smaller academic hospitals, community medical centers, and large private practices; however, interest from large academic centers continues to be strong. Particular interest exists regarding smaller and less-expensive proton therapy systems, especially the so-called “single-room” systems. In this paper, the advantages and disadvantages of 1-room proton therapy systems will be discussed. The emphasis on smaller and cheaper proton therapy facilities has also generated interest in new proton-accelerating technologies such as superconducting cyclotrons and synchrocyclotrons, laser acceleration, and dielectric-wall accelerators. Superconducting magnets are also being developed to decrease the size and weight of isocentric gantries. Another important technical development is spot-beam scanning, which offers the ability to deliver intensity-modulated proton treatments (IMPT). IMPT has the potential to provide dose distributions that are superior to those for photon intensity modulation techniques (IMXT) and to improve clinical outcomes for patients undergoing cancer therapy. At the present time, only two facilities one in Europe and one in the United States have the ability to deliver IMPT treatments, however, within the next year or two several additional facilities are expected to achieve this capability.