With a background in heavy-ion physics from Frankfurt University, it would have been hard for me not to have heard of this project before: Kind of a large spin-off of the GSI facility near Darmstadt, the Heidelberg Ion-Beam Therapy Center is a dedicated heavy-ion accelerator for deployment in radiotherapy to treat tumours. It is the first medical heavy-ion machine in Europe.
The building, half-buried in the ground to minimise radiation exposure for the environment, houses an ion source, a linear accelerator (LINAC) and a synchrotron with a circumference of 65 metres, which can accelerate protons (hydrogen nuclei), alpha particles (helium nuclei), or nuclei of carbon and oxygen to final energies of 50 to 430 MeV/nucleon. For carbon nuclei with 12 nucleons, this means a maximal energy of 5.16 GeV. This energy corresponds to a bit less than half the rest mass of the carbon nucleus, meaning a gamma factor of 1.45, or motion of the nucleus at 73 percent of the speed of light.
The heavy-ion beam, which is focussed to a diameter of about a millimetre, is steered by the high energy beam transport (HEBT) system to one of two treatment places, or into a big, pivotable installation of bending magnets, the so-called gantry. The gantry allows the beam to be directed from any direction of a vertical plane into one point.
At the treatment places, the beam, which is focussed to a diameter of about a millimetre, enters the body of patients, and deposits its energy in tumour cells, thereby corrupting the DNA of the tumour cells and stopping their runaway replication.
What is so special about heavy ions for the treatment of cancer that justifies the construction of a large, highly specialised 120 million Euro facility?
It's an effect discovered in 1904 by the Australian physicists William H. Bragg and Richard D. Kleeman, who studied energy energy deposition of alpha particles from radioactive decays when penetrating matter. To their surprise, and different from gamma rays or X rays, alpha particles deposit their energy predominantly around the end point of their track.
On a plot showing energy deposition along the path, this pattern shows up as a curve strongly peaked at the end point, in the so-called Bragg peak. (The Bragg peak should not be confused with the Bragg reflections in X ray scattering, which were discovered by William H. Bragg and his son, William Lawrence, in 1913, winning them the 1915 Nobel Prize in physics.)
This strongly localised energy deposition, along with the sharp focus of the beam, makes heavy ions such as carbon an ideal tool to attack tumour cells while doing as less harm as possible to the surrounding tissue. The penetration depth can be controlled by the ion beam energy. Thus, the ion beam hits its target precisely and transfers an exact dosage of energy to the tumour.
HIT will be used to treat tumours which are deeply situated in the body and can hardly be reached by conventional radiation treatment. Tests at GSI so far have been very promising, and there are good chances that a large part of the about 1300 patients per year who will be treated at HIT eventually can be cured.
- Web page of the Heidelberg Ion-Beam Therapy Center (HIT)
- Photo Gallery of the HIT
- HIT Brochure as PDF file
- For technical details about the accelerator facility, check out T. Winkelmann et al, "Experience at the Ion Therapy Center (HIT) with two years of continuous ECR ion source operation", Proceedings of ECRIS08, Chicago, IL USA (PDF file).
- About the costs of HIT, check out e.g O. Jäkel et al.: "On the cost-effectiveness of Carbon ion radiation therapy for skull base chordoma.", Radiotherapy and Oncology 83(2) (2007) 133-8.