"Entwicklung und Klinische Implementierung neuer Verfahren zur Dosismessung in der Strahlentherapie mit Schwerionen"
Zusammenfassung der Projektergebnisse
Ion beam therapy for cancer treatment is a highly conformal radiation therapy. To exploit its full potential for patient treatments, it is needed to improve the detection possibilities of ion beams. The aim of our project was to find a measurement method which would increase the spatial resolution for patient plan verifications prior to the treatment. All the experiments were performed at the Heidelberg Ion Beam Therapy Facility (HIT) in Germany. Two-dimensional detectors with high spatial resolution (radiochromic EBT films, flat-panel detector and crystalline silicon detector) were analysed as alternatives to the standard system composed of an array of pin-point ionization chambers. The flat-panel detector was evaluated as the most promising candidate for the near future. It provides sufficient spatial resolution, large sensitive area and online readout. A good homogeneity of the response can be reached by using the developed correction procedure. An excellent longtime stability of the detector response was found (±0.5% in 15 months), reflecting no signs of radiation damage, which has to be further monitored. The found linearity of the response with the fluence rate simplifies quantitative measurements. For patient plan verifications a new method was developed, based on absolute two-dimensional fluence measurements in the plateau. For this purpose the detector response was calibrated in terms of fluence. Quantitative tests using real patient treatment plans have shown very good agreement between the measured fluence distributions and the calculations of the treatment planning system using an evaluation algorithm based on the gamma-index analysis. This method provides a 150-times higher spatial resolution than the standard method. Therefore it is especially valuable for strongly inhomogeneous treatment fields. Since this technique does need a water phantom, it can be used with a gantry, where is a lack of alternative methods. Although it does not provide dose measurements in depth, the dose can be calculated from the measured fluence distributions using the strictly controlled energies at HIT. In this way it is also feasible to recalculate the dose distribution on a patient CT to evaluate the effects of disagreements, what is a clear advantage of the new technique. The cost of the flat-panel detector is acceptable and also its practical properties (size, weight, simplicity) make it feasible to be used in daily clinical routine. Therefore newly developed technique has a good perspective for clinical application as soon as legal issues with its implementation for this purpose are clarified. As a side-effect of the project, it was found that the flat-panel detector is suitable for daily quality assurance measurements including beam spot position and shape as well as homogeneity of scanned fields. Its use in the clinical practice will enable time saving corresponding to about one patient treatment per day. It gains further importancy due to finished production of the used film type and non-availability of equivalent alternative detectors. From the perspective of the results reached by electronic detectors, EBT films represent a too slow method to be used for patient plan verifications in the daily routine. However, it can be a useful tool for the determination of the dose on the skin during the therapy, as requested in some countries. The independency of the response on the beam energy, caused by orders of magnitude higher saturation dose, is represents an advantage in comparison to radiographic films. The response of the Timepix detector was tested in medical ion beams. It provides increased spatial resolution and high sensitivity which enable to register single particles online and provides energy loss measurements for high energetic protons and carbon ions using the energy calibration. The investigations show that the response has also sensitivity to different particle types. With respect to its price, we conclude that the flat-panel detector is a suffcient canditate to be used for patient plan verifications in the near future. However, the superb capabilities of the Timepix detector make it a promising candidate to deliver diverse information desired in ion beam therapy, unaccessible to other detectors.
Projektbezogene Publikationen (Auswahl)
- Dosimetric properties of Gafchromic EBT films in medical carbon ion beams, Phys. Med. Biol. 55 5557-67 (2010)
M. Martišíková and O. Jäkel
- Dosimetric properties of Gafchromic EBT films in monoenergetic medical ion beams, Phys. Med. Biol. 55 3741-51 (2010)
M. Martišíková and O. Jäkel
- Gafchromic EBT films for ion dosimetry, Radiation Measurements 45 1268-70 (2010)
M. Martišíková, O. Jäkel
- Study of Gafchromic EBT film response over a large dose range, Phys. Med. Biol. 55 N281-90 (2010)
M. Martišíková and O. Jäkel
- Test of an amorphous silicon detector in medical proton beams, Nucl. Instrum. Meth A 633 Supplement 1 S259-61 (2010)
M. Martišíková, B. M. Hesse, O. Jäkel
- Measurement of secondary radiation during ion beam therapy with the pixel detector Timepix, Journal of Instrumentation 6 C11014 (2011)
M. Martišíková, J. Jakubek, C. Granja, B. Hartmann, L. Opálka, S. Pospíšil and O. Jäkel
- Selective detection of secondary particles and neutrons produced in ion beam therapy with 3D sensitive voxel detector, Journal of Instrumentation 6 C12010 (2011)
J. Jakubek, C. Granja, B. Hartmann, O. Jäkel, M. Martisikova, L. Opalka and S. Pospisil
