Disadvantages Of Proton Therapy

2.1 Proton therapy
The first who came up with the idea to use accelerated protons in cancer radiation therapy was Robert Wilson in 1946 [6]. In his paper he stated the basic principles and potential of this discipline. After the paper was published it took 8 years before the first proton therapy treatment took place in Berkeley [7], followed by Uppsala in 1957. The accelerators used for these treatments were based on existing particle accelerators designed for fundamental research. The applications were limited to a few areas of the body, such as eye tumours and head-neck tumours, since those accelerators were not designed for the treatment of patients and the energy was too low to treat deep-seated tumours. However, this pioneering work opened

This is the greatest advantage of proton therapy. Due to this characteristic energy deposition, protons maximize the damage to the tumour, while limiting the dose deposition in healthy tissue. This is especially important for tumours close to radiosensitive tissue, such as the spinal cord. The maximum energy that is needed for the proton beams is of the order of 200MeV. Since protons with an energy of 200 MeV reach depths of around 25 cm, this energy is suitable to treat deep-seated tumours. The maximum beam current is limited by the amount of dose that is delivered to the tissues: typically 2 Gy per litre per minute, with irradiated volumes being much smaller, this leads to a beam current of 1nA on

For radiotherapy, the doses are given in 30 − 35 fractions spread over 6 − 7 weeks, to allow healthy tissue to repair. This treatment plan is used both for conventional radiotherapy, as for proton therapy. However, if it is possible to improve the imaging techniques for proton therapy, such as proton radiography, the number of fractions may be reduced.
The greatest advantage of proton therapy, i.e. its localised dose deposition can turn into a disadvantage if the position of the tumour is not precisely determined. Then the healthy tissue is damaged while the tumour does not get the required dose. At this moment, there is an uncertainty on the position where the protons are most likely stopped due to conversion flaws between Hounsfield values 2 and Proton Stopping Power. Since there is no unique relation between the stopping power and the Hounsfield values, this leads to errors in the calculated position of the tumour from several millimetres up to 1cm.
Therefore, to exploit the full potential of proton therapy, new imaging techniques have to be developed that deal with these complications, one of these is proton radiography, which is the main topic of this