Steering particle beams against cancer
Steering particle beams against cancer
Dr Mario Ciocca - Head of Medical Physics Department
It is true that with the particle beams used today against cancer it will also be possible to treat the heart?
In principle, the cases in which hadrontherapy can be used may include neoplasms that affect the heart muscle or even non-oncological applications, such as the elimination of cardiac arrhythmias, in particular with the high-energy carbon ion beams used, for example, at CNAO.
However, as shown in recent studies conducted on a pig at the GSI nuclear research centre in Darmstadt in Germany, from a technological point of view the major obstacle in cardiac or para-cardiac treatments is the need to properly manage the movement of the organ associated to the patient's breathing (today this is feasible and safe, and already being used at CNAO in abdominal treatments), and the movement relating to the heartbeat, on which there is still much work to be done instead.
At CNAO, for example, we used carbon ions to treat some cases of tumours radio-resistant to traditional radiotherapy (photons) and heart-related ones; but we started the treatment only after radiological tests guaranteed us that the heartbeat did not significantly affect localizing the tumour volume and the characteristics of the area adjacent to it, crossed by radiation beams.
In summary, therefore, in the future neoplasms and some types of non-oncological cardiac dysfunctions may benefit from non-invasive treatments with high-energy, heavy charged particles beams, but the complexity of dealing with heart beat turns this into a method that is not quite ready yet for clinical use, except in very specific and favourable cases.
In addition to protons and carbon ions, will other particles and other materials be used in the future?
Radiation therapy with heavy charged particles is now an established worldwide option to treat specific types of neoplasms, in particular those that are radio-resistant to traditional treatments (i.e. with photons) and paediatric solid tumours. At present, the particles used in modern hadrontherapy are high energy protons and carbon ions.
On the other hand, the hospital-type centres (such as HIT; CNAO, MedAustron) equipped with synchrotrons with active dose distribution systems and capable of accelerating ions of different types, from protons to oxygen, that have been inaugurated re-opens interesting therapeutic perspectives. In particular, the clinical use of fast helium ion beams. Pioneering experiences with them date back to the 1980s in the USA (Lawrence Berkeley Laboratory), and it seems particularly favourable and worthy of being studied, especially in critical situations such as paediatric tumours (Kramer M et al, Medical Physics, vol. 43, 2016).
In fact, helium ions will be able to bridge the gap between protons and carbon ions, both physically and radiobiologically, thanks to their properties to intermediate. In terms of interaction with tissues, helium is less affected than carbon by the end-of-range nuclear fragmentation phenomenon, as well as by the typical scattering processes compared to proton beams.
Furthermore, their biological effectiveness, i.e. the ability to damage biological tissues (in particular, the DNA of cancer cells) is precisely intermediate between that of the other two particles widely used so far in clinical settings. The results of in vitro experiments (i.e. cell culture) with high energy helium ions, which are currently in progress at the centre of Heidelberg (HIT), are truly encouraging.; Once the necessary ministerial permits are obtained, CNAO is also expected to start experimenting with this type of ion, first at physical and radiobiological level, and finally clinically, in the coming years.
How fast do particles move in the accelerator? How can you steer them accurately towards the tumour?
Protons and carbon ions reach very high speeds, close to the speed of light (230,000 km per second for the maximum energy that can be reached).
Beam dimensions are adjusted thanks to magnets which are called "quadrupoles".
In this way, the accelerator physicists manage to guarantee full control of the beam size during while treating the tumour. In order to direct particles to the right point, dipoles and correctors are used instead. Correctors, called "special magnets", communicate directly with the Dose Delivery device (the active scanning system of CNAO).
The special magnets are installed at a short distance from the patient and are able to brush the tumour slices very quickly: in this way, optimal control of the dose released in each single slice of the tumour is obtained.