Only few ten radiotherapy facilities worldwide provide ion beams, in spite of their physical advantage of better achievable tumor conformity of the dose compared to conventional photon beams. Since mainly the large size and high costs hinder their wider spread, great efforts are ongoing to develop more compact ion therapy facilities.
Despite the considerable progress in the field over the past few years, a clinical operation of a laser-based proton therapy facility with high probability can be expected within one decade from now.
A dedicated eye tumor facility which requires only protons up to about 70 MeV and a fixed beamline could be set up faster for deep-seated tumors and may be helpful for developing and establishing laser-based technology.
However, because of the low number of patients, an exclusive development of a laser-driven eye treatment facility itself would not significantly contribute to an improved treatment of cancer patients in total.
Another helpful possibility may be the establishment of a laser system for measurements of radiobiological effectiveness in vivo and in vitro without clinical certification.
The progress of compact conventional proton accelerators over recent years leads presently to a rapidly increasing number of operating systems which may result in saturation of the number of proton facility installations in developed countries in some years. Nevertheless, there are three possibilities for a still ongoing need of laser-based therapy facilities.
Ion therapy versus photon beam therapy
First, running and future clinical trials comparing the clinical benefit of ion versus photon beam therapy reveal an unexpected higher advantage of ion therapy, i.e. much more than 14% of the patients can profit from ion irradiation, which will increase the number of facilities required for saturation.
Second, the reduction in costs by laser-based therapy facilities compared to conventional ion therapy is so strong, that new installations will use it in the developing countries. Third, heavier ions result in clinical benefit over protons for a larger number of patients, motivating the installation of cost-effective compact laser-based ion therapy facilities.
Furthermore, conventional proton therapy facilities have also experienced a huge effort to compact the facilities within the last decade. The most important progress was achieved by the introduction of superconducting proton cyclotrons, which shrink the diameter of the cyclotron from about 4 m to less than 2 m, connected also with a change in beam properties.
For instance, the maximum current is decreased and the beam is delivered within macro pulses with a duration of some ls and a repetition rate of about some kHz. Nevertheless, one room solutions are now commercially available for protons by directly mounting the superconducting cyclotron on a gantry. In contrast to protons, progress towards more compact conventional facilities for heavier ions, which require synchrotrons, is almost non-existent.