## 1 Preamble  
About 4% of people in developed countries are diagnosed with cancer each year and more than 50% of these patients receive radiation treatment, making radiotherapy, along with surgery, the most common, as well as the most successful form of cancer therapy. Although radiotherapy is predominantly performed using photons, proton therapy is quickly gaining popularity due to its ability to irradiate tumors with higher doses and greater spatial selectivity (localization). This means that with protons (and other ions) healthy tissue can be more readily spared during irradiation than using electron or photon therapy. However, patient access to proton and heavy ion (C\({}^{+6}\)) treatment is highly restricted due to high cost and consequent limited availability.  
The use of charged hadrons in cancer therapy is almost as old as the discovery and development of the cyclotron in 1932. The first suggestion that fast protons could be used in radiology was made by [PERSON] in 1946 [1] although it was not until 1954 that the first patients were treated. According to Wikipedia [2], as of 2012 there were 39 particle therapy facilities in the world located in Canada, China, Czech Republic, France, Germany, Italy, Japan, South Korea, Poland, Russia, South Africa, Sweden, Switzerland, the UK and the USA. More than 50% of the centers, however, are in the USA and Japan. Almost 100,000 patients have been treated with hadrons (protons and carbon ions). To treat tumors that are deeply seated within the body, proton energies above 250 MeV are needed while for carbon ions 400 MeV/amu is required.  
Nonetheless, radiotherapy using accelerator based hadron beams is well-established. A selection of the many excellent publications on this subject is given in references [3; 4; 5; 6; 7; 8; 9; 10; 11; 12]. The authors of reference [3] claimed that \"if 200 MeV proton accelerators would be as cheap and small as the 10 MeV electron linacs used in conventional radiotherapy, at least 90% of the patients would be treated with proton beams\". This indicates how effective hadron therapy is in cancer treatment. However caution must be exercised with this statement because there are very few randomized controlled trials comparing treatment with protons and photons (we further address this issue later in this work).  
As stated earlier, what is hampering the wider application (and access) of this therapy mode around the world is the high cost of these centers. The authors of [3] estimate that the cost of establishing a conventional accelerator-based hadron therapy center is in the range, 130-150 MeV which is prohibitive for many developing countries (relevant cost comparisons will be subsequently addressed in this work).  
Regarding future perspectives, the authors of [3] have stated that \"further in the future, the first proton single room facility based on the illumination of a thin target with powerful (10\({}^{18}\)-10\({}^{20}\) W\(\cdot\)cm\({}^{-2}\)) and short (30-50 fs) laser pulse is expected\". The basis of their statement is a shared optimism that the cost and size of laser-based proton therapy centers might be greatly reduced in the future [5]. Reduced cost and size will be critical for facilitating general access to hadron radiotherapy. In fact, a reasonable design constraint for the future is that full systems (novel sources, laser-based or otherwise, and other associated treatment components) should be accommodated within the infrastructure of existing hospitals (a consistent prediction has been made by [PERSON] _et al._ (see Section 3.3)).  
The overall challenge for laser-driven ion beam radiotherapy is to develop well-controlled, reliable energetic ion beams of very high quality that can meet stringent medical requirements with respect tophysical parameters and performance and therefore represent a viable alternative in an advancing state-of-the-art for radiotherapy.