Ion Beam Therapy: Principles and Quality Assurance - Short Course

Gerhard Kraft studied Physics at Heidelberg and Cologne where he received his Ph.D. in nuclear physics. He founded the biophysics department at GSI where he developed the heavy ion tumor therapy together with Wilma K. Weyrather. She studied Physics at the University of Cologne and received her Ph.D. at the University of Giessen in Radiobiology in 1978. They both together initiated the Radiobiology program at GSI and later on the tumor therapy.

The novel features of the GSI tumor therapy are the extreme target conform beam delivery using an intensity modulated scanning method, the biology based treatment planning and the in vivo control of the patient using online-PET. In order to cover the target with a dose having a homogenous biological effect and a steep gradient at the borders the Target volume is dissected in slices of equal particle energy which are covered by a grid of 20,000 to 50,000 pixels of different beam positions. For all these pixels the individual covering of particles has to be calculated according to the wanted dose level and the actual value of the Relative Biological Effectiveness, RBE, at the specific pixel. These RBE values depend on the physical composition of the beam at each location and the biological properties of the affected tissue mainly on its repair capacity of complex DNA damage.

For the clinical success of the up to now more than 400 patients treated with this technique, the quality assurance of the technical equipment, the biological modelling for the treatment planning and the physical dose delivery are extremely important.

The biological corrections of the treatment planning are based on the Local Effect Model LEM verified in many experiments. It is also confirmed by the follow up of the treated patients that did not show large side and late effects. For the quality assurance of the beam delivery an online measurement of the emission of gamma quants have been developed and used during patient irradiation. When penetrating through the patient a significant fraction of the primary beam such as carbon or other ions under go nuclear reaction with the tissue resulting in radioactive positron emitting isotopes either from the beam such as 11C and 10C or from the target atoms such as 15O. Their positron decay can be monitored from outside and can be used to track the beam stopping inside the patient.

Fine Fiedler did her Ph.D. in 2008 at the Technical University of Dresden and studied the feasibility to monitor the stopping points of the beam inside the patients. She is working in the In-beam-PET group of the Oncoray Dresden. She will report that the PET techniques are capable assessing the relevant parameters for quality assurance in respect to anatomical landmarks. But it has been also shown that it is possible to extend this technique to other ion than carbon such as Protons, 3He, 7Li and 16O.

In general, the short course will introduce in the physical and biological rational of ion beam therapy. It will explain the critical feature in planning and beam delivery and will give the principles for quality assurance.