Particle Therapy Positron Emission Tomography (PT-PET) for Treatment Verification


Particle Therapy Positron Emission Tomography (PT-PET) for Treatment Verification

Fiedler, F.

Radiation therapy is an important treatment modality in cancer therapy. New radiation species, like protons and light ions have the potential of increasing tumor conformality of irradiation. Because of the way these particles deposit their energy on their path through tissue they allow for an increased dose deposition in the tumor volume and reduce the damage of the surrounding normal tissue.
High precision radiotherapy treatment requires efficient quality assurance techniques. Even small changes in the irradiated volume will lead to a mismatch of the deposited dose maximum and the tumor. This causes missing dose in the tumor volume and potential damage to normal tissue. Therefore, a treatment verification system is highly desirable. Between 1997 and 2008, the in-beam Positron Emission Tomography (PET) method was used at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany to monitor the dose delivered by 12C beams [1]. This method makes use of the β+-activity produced via nuclear interactions between the therapeutic beam and the patient tissue. The results and experiences of the clinical application of in-beam PET for carbon ions GSI will be shown. Based on this experience several approaches to improve the significance of the result have been studied.
Since the dose delivery is evaluated by means of a comparison between measured and simulated data a reliable prediction of β+-activity is crucial. To model the positron emitter production accurately, cross sections for all possible nuclear reactions occurring in the tissue during irradiation which lead to positron emitters are required. Since these cross sections are available only for a few reaction channels in the required energy range, a novel approach for estimating the positron emitter production from experimental data is introduced [2].
Up to now the comparison of the distributions is performed by well-trained observers (clinicians, physicists). This process is very time consuming and low in reproducibility. Therefore, a semi-automatic method has been developed evaluating the range and including a cavity filling detection algorithm. System inherent uncertainties are handled by means of a statistical approach [3, 4].
The Particle Therapy (PT)- PET method has been approved for static tumors under clinical conditions. However, also for intra-fractionally moving targets, the 4D simulation [5] as well as the 4D reconstruction [6] of PT-PET data has been established. By means of dedicated 4D-PET experiments the results of the comparison between measured and anticipated activities have been investigated.
References
[1] W. Enghardt, et al., Nucl. Instr. Meth A 525, 2004.
[2] M. Priegnitz, et al., IEEE Trans. Nucl. Sci. 59, 2012.
[3] S. Helmbrecht, et al., Phys. Med. Biol. 57, 2012.
[4] P. Kuess, et al., Med. Phys. 39, 2012.
[5] K. Laube, et al., Phys. Med. Biol. 58, 2013.
[6] K.Stützer, Phys. Med. Biol. 58, 2013.

  • Invited lecture (Conferences)
    Workshop on Range Assessment and Dose Verification in Particle Therapy, 29.-30.09.2014, Dresden, Deutschland

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Publ.-Id: 21006