Extension and validation of an analytical model for in vivo PET verification of proton therapy--a phantom and clinical study.

The interest in positron emission tomography (PET) as a tool for treatment verification in proton therapy has become widespread in recent years, and several research groups worldwide are currently investigating the clinical implementation. After the first off-line investigation with a PET/CT scanner at MGH (Boston, USA), attention is now focused on an in-room PET application immediately after treatment in order to also detect shorter-lived isotopes, such as O15 and N13, minimizing isotope washout and avoiding patient repositioning errors. Clinical trials are being conducted by means of commercially available PET systems, and other tests are planned using application-dedicated tomographs. Parallel to the experimental investigation and new hardware development, great interest has been shown in the development of fast procedures to provide feedback regarding the delivered dose from reconstructed PET images. Since the thresholds of inelastic nuclear reactions leading to tissue ß+ -activation fall within the energy range of 15-20 MeV, the distal activity fall-off is correlated, but not directly matched, to the distal fall-off of the dose distribution. Moreover, the physical interactions leading to ß+ -activation and energy deposition are of a different nature. All these facts make it essential to further develop accurate and fast methodologies capable of predicting, on the basis of the planned dose distribution, expected PET images to be compared with actual PET measurements, thus providing clinical feedback on the correctness of the dose delivery and of the irradiation field position. The aim of this study has been to validate an analytical model and to implement and evaluate it in a fast and flexible framework able to locally predict such activity distributions directly taking the reference planning CT and planned dose as inputs. The results achieved in this study for phantoms and clinical cases highlighted the potential of the implemented method to predict expected activity distributions with great accuracy. Thus, the analytical model can be used as a powerful substitute method to the sensitive and time-consuming Monte Carlo approach.

Comparison of two dedicated 'in beam' PET systems via simultaneous imaging of (12)C-induced beta(+)-activity.

The selective energy deposition of hadrontherapy has led to a growing interest in quality assurance techniques such as 'in-beam' PET. Due to the current lack of commercial solutions, dedicated detectors need to be developed. In this paper, we compare the performances of two different 'in-beam' PET systems which were simultaneously operated during and after low energy carbon ion irradiation of PMMA phantoms at GSI Darmstadt. The results highlight advantages and drawbacks of a novel in-beam PET prototype against a long-term clinically operated tomograph for ion therapy monitoring.

Experimental validation of the filtering approach for dose monitoring in proton therapy at low energy.

The higher physical selectivity of proton therapy demands higher accuracy in monitoring of the delivered dose, especially when the target volume is located next to critical organs and a fractionated therapy is applied. A method to verify a treatment plan and to ensure the high quality of the hadrontherapy is to use Positron Emission Tomography (PET), which takes advantage of the nuclear reactions between protons and nuclei in the tissue during irradiation producing beta(+)-emitting isotopes. Unfortunately, the PET image is not directly proportional to the delivered radiation dose distribution; this is the reason why, at the present time, the verification of depth dose profiles with PET techniques is limited to a comparison between the measured activity and the one predicted for the planned treatment by a Monte Carlo model. In this paper we test the feasibility of a different scheme, which permits to reconstruct the expected PET signal from the planned radiation dose distribution along beam direction in a simpler and more direct way. The considered filter model, based on the description of the PET image as a convolution of the dose distribution with a filter function, has already demonstrated its potential applicability to beam energies above 70 MeV. Our experimental investigation provides support to the possibility of extending the same approach to the lower energy range ([40, 70] MeV), in the perspective of its clinical application in eye proton therapy.

[Autoantibodies in chronic hepatitis C. Markers of autoimmunity or non-specific events?]. / Autoanticorpi nell'epatite cronica da virus C. Marcatori di autoimmunità o eventi aspecifici?

In the light of the high prevalence of non organ-specific autoantibodies in chronic hepatitis C, the possibility that such a finding may represent the consequence of a viral, autoimmune or overlapping disease should be considered, which may in turn require a different therapeutical approach. It is known, anyway, that the diagnosis of autoimmune hepatitis is based on a set of epidemiological, clinical, biochemical, histological criteria and autoantibody pattern. In 113 cases of chronic hepatitis with HCV infection, we determined the presence of non organ-specific autoantibodies [anti-nuclear (ANA), anti-smooth muscle (SMA), anti-liver-kidney microsomal antibodies (LKM), anti-mithocondrial antibodies (AMA)] and described the epidemiological, clinical, biochemical, histological characteristics and therapeutic response to interferon. 40 patients (35%) exhibited non organ-specific autoantibodies: 25 patients were SMA positive (Vasal pattern), 4 ANA positive (Speckled pattern), 7 ANA (Speckled pattern) + SMA (Vasal pattern) positive and 4 LKM positive. All subjects with HCV infection and autoantibodies did not display additional criterias of autoimmunity, including the same outcome to interferon therapy when compared to HCV positive patients without autoantibodies. The failure to determine clinical features, associated to autoimmunity in HCV positive patients with autoantibodies, suggests that autoantibody occurrence may represent a fortuitous event during the course of HCV infection.