In-beam Positron Emission Tomography Research Articles

Random coincidences during in-beam PET measurements at microbunched therapeutic ion beams

Abstract At the experimental carbon ion tumour therapy facility at GSI Darmstadt, in-beam positron emission tomography (PET) is used to monitor the dose delivery precision. A dual head positron camera has been assembled from commercial detector components in order to measure the β + -activity, induced by the irradiation, simultaneously to the dose application. Despite the positive clinical impact, the image quality is limited by the low counting statistics, orders of magnitude below that in standard PET applications to nuclear medicine. This paper investigates the origin for the noisy acquisition during particle extraction from the synchrotron of GSI. The results demonstrate the failure of standard random correction techniques due to a γ -ray background correlated in time with the carbon ion beam microstructure. This prevents the use of data acquired during beam extraction for imaging. The loss of counting statistics is expected to rise further at the future hospital-based facility at Heidelberg, due to a more efficient utilisation of the accelerator resulting in shorter beam pauses and a reduced treatment time. In this respect, this paper provides the basis for a new data acquisition concept tailored to the unconventional application of in-beam PET imaging to therapy monitoring at radiofrequency pulsed radiation sources.

Dose quantification from in-beam positron emission tomography

Positron emission tomography (PET) imaging of the radioactivity distributions induced by therapeutic irradiation is at present the only feasible method for an in situ and non-invasive monitoring of radiooncology treatments with ion beams. The clinical implementation of this imaging technology at the experimental carbon ion therapy facility at the Gesellschaft für Schwerionenforschung (GSI) at Darmstadt, Germany is outlined and an interactive approach for a PET guided quantification of local dose deviations with respect to the treatment plan is presented.

The modelling of positron emitter production and PET imaging during carbon ion therapy

At the carbon ion therapy facility of GSI Darmstadt in-beam positron emission tomography (PET) is used for imaging the β+-activity distributions which are produced via nuclear fragmentation reactions between the carbon ions and the atomic nuclei of the irradiated tissue. On the basis of these PET images the quality of the irradiation, i.e. the position of the field, the particle range in vivo and even local deviations between the planned and the applied dose distribution, can be evaluated. However, for such an evaluation the measured β+-activity distributions have to be compared with those predicted from the treatment plan. The predictions are calculated as follows: a Monte Carlo event generator produces list mode data files of the same format as the PET scanner in order to be processed like the measured ones for tomographic reconstruction. The event generator models the whole chain from the interaction of the projectiles with the target, i.e. their stopping and nuclear reactions, the production and the decay of positron emitters, the motion of the positrons as well as the propagation and the detection of the annihilation photons. The steps of the modelling, the experimental validation and clinical implementation are presented.

The LSO/APD array as a possible detector for in-beam PET in hadron therapy

We have studied the performance of finger-like LSO:Ce (LSO) crystals coupled one by one to pixels of avalanche photodiode detector (APD) arrays during their operation in coincidence at /sup 12/C ion beams of parameters being typical for tumor irradiations. In a first step of these experiments the parameters of the detectors and the signal processing setup have been characterized off-beam, i.e., by means of /spl beta//sup +/ radioactive sources (/sup 22/Na, /sup 68/Ge). Afterwards, the apparatus was installed at the medical beam line of the heavy ion synchrotron (SIS) of the Gesellschaft fu/spl uml/r Schwerionenforschung (GSI) at Darmstadt, Germany. Here the /spl beta//sup +/ activity produced by nuclear fragmentation reactions of /sup 12/C 200.3 AMeV heavy ion beams with polymerized methyl methacrylate phantoms were measured. Furthermore, a /sup 68/Ge source was included into the in-beam experiment, in order to check the stability of the setup and to compare energy and time resolution before, during, and after the phantom irradiations. Additionally, it could be demonstrated by means of high resolution /spl gamma/-ray spectroscopy that LSO is not activated by the light projectile fragments escaping the patients downbeam during therapeutic irradiations The experimental results indicate that LSO scintillator is a suitable material for in-beam positron emission tomography (PET) and, furthermore, the LSO/APD array is a feasible detector concept for in-beam monitoring of the dose application by means of PET.

Attenuation and scatter correction for in-beam positron emission tomography monitoring of tumour irradiations with heavy ions

An in-beam dual-head positron camera is used to monitor the dose application in situ during the tumour irradiation with carbon ion beams at the experimental heavy ion therapy facility at GSI Darmstadt. Therefore, a positron emission tomograph has been mounted directly at the treatment site. A fully 3D reconstruction algorithm based on the maximum likelihood expectation maximization (MLEM) algorithm has been developed and adapted to this spatially varying imaging situation. The scatter and attenuation correction are included in the forward projection step of the maximum likelihood image reconstruction. This requires an attenuation map containing the information on the material composition and densities. This information is derived from the x-ray computed tomograms of the patient and the patient fixation system including the head-rest. The normalization of scattered events relative to the unscattered events is done by a global scatter fraction factor which is estimated by means of a Monte Carlo simulation. The feasibility of the proposed algorithm is shown by means of computer simulations, phantom measurements as well as patient data.

Treatment planning for heavy ion radiotherapy: clinical implementationand application

The clinical implementation and application of a novel treatmentplanning system (TPS) for scanned ion beams is described, which is in clinicaluse for carbon ion treatments at the German heavy ion facility (GSI).All treatment plans are evaluated on the basis of biologically effective dosedistributions. For therapy control, in-beam positron emission tomography (PET)and an online monitoring system for the beam intensity and position are used.The absence of a gantry restricts the treatment plans to horizontal beams.Most of the treatment plans consist of two nearly opposing lateral fields orsometimes orthogonal fields. In only a very few cases a single beam was used.For patients with very complex target volumes lateral and even distal fieldpatching techniques were applied. Additional improvements can be achieved whenthe patient's head is fixed in a tilted position, in order to achievesparing of the organs at risk.In order to test the stability of dose distributions in the case of patientmisalignments we routinely simulate the effects of misalignments forpatients with critical structures next to the target volume.The uncertainties in the range calculation are taken into account by amargin around the target volume of typically 2-3 mm, which can, however, beextended if the simulation demonstrates larger deviations.The novel TPS developed for scanned ion beams was introduced into clinicalroutine in December 1997 and was used for the treatment planning of 63patients with head and neck tumours until July 2000. Planning strategies andmethods were developed for this tumour location that facilitate the treatmentof a larger number of patients with the scanned heavy ion beam in a clinicalsetting. Further developments aim towards a simultaneous optimization of thetreatment field intensities and more effective procedures for the patientset-up. The results demonstrate that ion beams can be integrated into aclinical environment for treatment planning and delivery.

NDE and fracture studies of hot-pressed Si3N4 37721 Roberts, R.A.; Singh, J.P.; Vaitekunas, J.J. Argonne National Laboratory, Illinois (United States), DE87-011481 21 pp. (Feb. 1987)

The benefit of using dedicated in-beam positron emission tomography (PET) detectors in the treatment room instead of commercial tomographs nearby is an open question. This work quantitatively compares the measurable signal for in-beam and offline PET imaging, taking into account realistic acquisition strategies at different ion beam facilities. Both scenarios of pulsed and continuous irradiation from synchrotron and cyclotron accelerators are considered, because of their widespread use in most carbon ion and proton therapy centers.A mathematical framework is introduced to compare the time-dependent amount and spatial distribution of decays from irradiation-induced isotope production. The latter is calculated with Monte Carlo techniques for real proton treatments of head-and-neck and paraspinal tumors. Extrapolation to carbon ion irradiation is based on results of previous phantom experiments. Biologic clearance is modeled taking into account available data from previous animal and clinical studies.Ratios between the amount of physical decays available for in-beam and offline detection range from 40% to 60% for cyclotron-based facilities, to 65% to 110% (carbon ions) and 94% to 166% (protons) at synchrotron-based facilities, and increase when including biologic clearance. Spatial distributions of decays during irradiation exhibit better correlation with the dose delivery and reduced influence of biologic processes.In-beam imaging can be advantageous for synchrotron-based facilities, provided that efficient PET systems enabling detection of isotope decays during beam extraction are implemented. For very short (<2 min) irradiation times at cyclotron-based facilities, a few minutes of acquisition time after the end of irradiation are needed for counting statistics, thus affecting patient throughput.

Processing of real-time images for quantitative neutron radiography : 37863 Polichar, R.; Shreve, D. Neutron Radiography, Proceedings of the Second World Conference, Paris (France), 16–20 Jun. 1986. pp. 587–594. D. Reidel Publishing Company

The benefit of using dedicated in-beam positron emission tomography (PET) detectors in the treatment room instead of commercial tomographs nearby is an open question. This work quantitatively compares the measurable signal for in-beam and offline PET imaging, taking into account realistic acquisition strategies at different ion beam facilities. Both scenarios of pulsed and continuous irradiation from synchrotron and cyclotron accelerators are considered, because of their widespread use in most carbon ion and proton therapy centers.A mathematical framework is introduced to compare the time-dependent amount and spatial distribution of decays from irradiation-induced isotope production. The latter is calculated with Monte Carlo techniques for real proton treatments of head-and-neck and paraspinal tumors. Extrapolation to carbon ion irradiation is based on results of previous phantom experiments. Biologic clearance is modeled taking into account available data from previous animal and clinical studies.Ratios between the amount of physical decays available for in-beam and offline detection range from 40% to 60% for cyclotron-based facilities, to 65% to 110% (carbon ions) and 94% to 166% (protons) at synchrotron-based facilities, and increase when including biologic clearance. Spatial distributions of decays during irradiation exhibit better correlation with the dose delivery and reduced influence of biologic processes.In-beam imaging can be advantageous for synchrotron-based facilities, provided that efficient PET systems enabling detection of isotope decays during beam extraction are implemented. For very short (<2 min) irradiation times at cyclotron-based facilities, a few minutes of acquisition time after the end of irradiation are needed for counting statistics, thus affecting patient throughput.

Improvement of reconstructed image quality in neutron CT : 37871 Matsumoto, G.; Sendo, T.; Honda, S.; Ohkubo, K.; Ikeda, Y. Neutron Radiography, Proceedings of the Second World Conference, Paris (France), 16–20 Jun. 1986. pp. 745–752. D. Reidel Publishing Company

The benefit of using dedicated in-beam positron emission tomography (PET) detectors in the treatment room instead of commercial tomographs nearby is an open question. This work quantitatively compares the measurable signal for in-beam and offline PET imaging, taking into account realistic acquisition strategies at different ion beam facilities. Both scenarios of pulsed and continuous irradiation from synchrotron and cyclotron accelerators are considered, because of their widespread use in most carbon ion and proton therapy centers.A mathematical framework is introduced to compare the time-dependent amount and spatial distribution of decays from irradiation-induced isotope production. The latter is calculated with Monte Carlo techniques for real proton treatments of head-and-neck and paraspinal tumors. Extrapolation to carbon ion irradiation is based on results of previous phantom experiments. Biologic clearance is modeled taking into account available data from previous animal and clinical studies.Ratios between the amount of physical decays available for in-beam and offline detection range from 40% to 60% for cyclotron-based facilities, to 65% to 110% (carbon ions) and 94% to 166% (protons) at synchrotron-based facilities, and increase when including biologic clearance. Spatial distributions of decays during irradiation exhibit better correlation with the dose delivery and reduced influence of biologic processes.In-beam imaging can be advantageous for synchrotron-based facilities, provided that efficient PET systems enabling detection of isotope decays during beam extraction are implemented. For very short (<2 min) irradiation times at cyclotron-based facilities, a few minutes of acquisition time after the end of irradiation are needed for counting statistics, thus affecting patient throughput.