The research group In-vivo Dosimetry for New Types of Radiation deals with the exploration of novel methods and with the development of clinically applicable instruments for precisely assessing the range of proton beams in the patient’s body during radio-oncological treatments.  Energetic protons of therapeutic beams are stopped in the body and deposit most of their kinetic energy in the last few millimeters of the beam track.  The proton range (or track length) depends on the initial proton energy.  This allows focusing the destructive radiation dose just on the tumor.  However, the actual depth of the dose deposition maximum is hard to assess just because beam particles do, in contrast to hard X-rays, not leave the body.
To visualize proton beams, the scientists decided to capture the prompt gamma rays produced occasionally by beam particles passing tissue.  Those gamma rays can be measured, for instance, with a Slit Camera as developed by Ion Beam Applications (IBA).  In a collaborative project involving both the In-vivo Dosimetry and the High-Precision Radiotherapy groups, OncoRay scientists managed for the first time ever to precisely track the proton beam in a patient during several sessions of a fractionated treatment (1,2,3,4), i.e., a treatment delivered in several separate sessions or fractions.

Prompt Gamma-Ray Timing

Graduate students setting up detectors and targets for an experiment in the treatment room of the Universitäts Protonen Therapie Dresden (UPTD). Six “proton stopwatches”, each consisting of a cerium bromide scintillation detector and a superfast digital spectrometer by Target Systemelektronik, are used to measure the range of proton beams.

Moreover, the research group In-vivo Dosimetry has proposed, patented, and investigated a novel method of range assessment, named Prompt Gamma-Ray Timing (PGT).  It is based on the accumulation of arrival time distributions of prompt gamma rays in appropriate detectors, measured with respect to the sharply bunched proton beam.  The width of such distributions reflects the overall stopping time of the proton bunches in tissue, which is well correlated with the stopping distance, i.e., with the proton range (5,6,7).  These time distributions shall be measured and compared with the corresponding spectra predicted on the basis of treatment plans in real time.  Distinct deviations between prediction and measurement could immediately interrupt the treatment.  The „proton stopwatch” could thus be used for quality assurance and as an effective safety element.  At present, the PGT technique is being explored experimentally and planned to be translated to clinical applications step by step.  Generally, PGT is much simpler than other techniques of range assessment and should result in less expensive, cheaper systems to be used in clinical routine.

Verifying and exploring novel concepts or techniques requires frequent experimental campaigns performed at particle accelerators in various research facilities or clinics.  Those are complemented with computer simulations that allow understanding and extrapolating the experimental findings.  Scientists of the In-vivo Dosimetry group intensely collaborate with other research groups, with specialists of other disciplines, as well as with innovative companies to translate innovative research in distinct benefit for the patients at minimum time.