A non Gaussian model for the lateral dose evaluation in hadrontherapy

Challenging issues in Treatment Planning System for hadrontherapy are the accurate calculation of dose distribution, the reduction in Memory space required to store the dose kernel of individual pencil beams and the shortening of computation time for dose optimization and calculation. In this framework, the prediction of lateral dose distributions is a topic of great interest because currently, a Double Gaussian parametrization is typically used as approximation although other parametrizations are also available. The best accuracy for this kind of calculations can be obtained by Monte Carlo (MC) methods, at the expense of a long computing time. As alternative, we propose a flexible model based on the full Molière theory for Coulomb multiple scattering. The use of the original equations of the theory allows to remove free parameters for the electromagnetic interaction with the advantage of full accuracy with a reasonable increase in the computing time. The contribution of the nuclear interactions are also fully taken into account with a two-parameters fit on FLUKA simulation and this part is added to the electromagnetic core with a proper weight. The model has been validate with MC simulations and with Heidelberg Ion-Beam Therapy Center (HIT) experimental data. In a second step, the model has been inserted in a research Treatment Planning System CERR - A Computational Environment for Radiotherapy Research at the Ludwig-Maximilians-Universitat Munchen, to compare its result against the ones obtained with the currently used Double Gaussian parametrization to evaluate the lateral energy deposition. A quantitative comparison has been done to evaluate the difference between a treatment plan obtained using the Double Gaussian parametrization and a treatment plan obtained using the model calculation, in the cases of a single beam and a full treatment plan in homogeneous water phantom and also a plan is performed in presence of inhomogeneities.Eine der anspruchsvollsten Herausforderungen in der Bestrahlungsplanung von Ionenstrahltherapie ist die präzise Berechnung der Dosisverteilung im Patienten, die Reduktion des Speicherbedarfs der Dosiskernel von einzelnen Pencil-beams, sowie die Verkürzung der Rechenzeit fur Dosisoptimierung und -berechnung. In diesem Rahmen ist die Berechnung der lateralen Protonen-Dosisverteilungen ein Thema von großem Interesse, da momentan eine Double Gaussian Parametrisierung als Näherung verwendet wird, obwohl weitere Parametrisierungen existieren. Die größte Genauigkeit fur diese Art von Berechnungen kann mit Monte Carlo (MC) Simulationen erzielt werden, jedoch auf Kosten langer Laufzeiten. Als Alternative wird in dieser Arbeit ein flexibles Modell vorgeschlagen, welches auf der vollständigen Moliere-Theorie fur Multiples Coulomb Streuung basiert. Die Verwendung der originalen Gleichungen der Theorie erlaubt die Reduktion der freien Parameter für die elektromagnetischen Wechselwirkungen, was den Vorteil der vollen Genauigkeit mit einer moderaten Erhöhung der Rechenzeit vereint. Der Beitrag von nuklearen Wechselwirkungen wird mit einem zwei-Parameter Fit an FLUKA Simulationen berucksichtigt und dieser Anteil wird dann zu dem elektromagnetischen Core mit einer Gewichtung addiert. Das Modell wurde in das Forschungs-Bestrahlungsplanungssystem CERR A Computational Environment for Radiotherapy Research implementiert, um die Ergebnisse bei der lateralen Dosis-Deposition mit der momentan verwendeten Double Gaussian Parametrisierung zu vergleichen. Ein quantitativer Vergleich wurde durchgeführt zwischen den Bestrahlungsplänen die einmal mit der Double Gauss Parametrisierung und einmal mit dem vorgeschlagene Modell berechnet wurden. Das untersuchte Szenario beinhaltete Pläne die entweder für einzelne Strahlen verschiedener Energien in einem homogenen Wasserphantom, ein voller Bestrahlungsplan in einem homogenen Wasserphantom, sowie einzelne Strahlen verschiedener Energien für ein Phantom mit Inhomogenitäten berechnet wurden.Temi di grande interesse nell’ambito dello sviluppo dei Software per il calcolo di piani di trattamento per adroterapia (Treatment Planning System (TPS)), sono la riduzione dei tempi computazionali del calcolo e dell’ottimizzazione della dose, e la riduzione della memoria richiesta per l’archiviazione della dose di ogni singolo fascio (pencil beam). In questo contesto, la valutazione della distribuzione laterale della dose è un argomento di grande interesse in quanto attualmente viene utilizzata una funzione a doppia gaussiana come approssimazione, che risulta non completamente accurata. Altre parametrizzazioni sono disponibili; anch’esse rimangono però approssimazioni. La migliore accuratezza per questo tipo di calcolo della dose viene ottenuta utilizzando le tecniche Monte Carlo (MC)che richiedono però tempi computazionali molto lunghi. In alternativa, questo lavoro propone un modello flessibile e analitico basato sulla teoria completa di Moli`ere per la valutazione dello scattering multiplo di Coulomb. L’utilizzo delle equazioni originali di questa teoria permette di rimuovere ogni parametro libero per il calcolo delle interazioni elettromagnetiche, ottenendo così il vantaggio di un’accuratezza pari a quella del metodo MC ma con tempi di calcolo di molto inferiori. Il contributo delle interazioni nucleari è considerato tramite un fit, con soli due parametri, sulle simulazioni MC FLUKA. La funzione viene aggiunta alla parte analitica elettromagnetica assegnando ad entrambe un fattore di peso di senso fisico, calcolato appropriatamente. Il modello così ottenuto è stato validato con simulazioni MC e con dati sperimentali del centro di adroterapia di Heidelberg, Heidelberg Ion-Beam Therapy Center (HIT). Successivamente, il modello è stato inserito nel TPS di ricerca CERR - A Computational Environment for Radiotherapy Research presso l’Università di Monaco Ludwig-Maximilians-Universitat Munchen, per confrontare i risultati ottenuti valutando piani di trattamento che utilizzano l’approssimazione gaussiana per il calcolo della dose, con piani ditrattamento che utilizzano il modello per il calcolo della dose stessa. Uno studio quantitativo è stato svolto considerando i casi di: singoli fasci di energia fissata in un fantoccio di acqua omogeneo, un piano di trattamento completo (come caso reale della pratica clinica, che considera più fasci di diverse energie e posizioni) in un fantoccio di acqua omogeneo, e infine i casi di singoli fasci a energie fissate in fantocci che presentano disomogeneità

A non Gaussian model for the lateral dose evaluation in hadrontherapy: development and Treatment Planning System implementation

Challenging issues in Treatment Planning System for hadrontherapy are the accurate calculation of dose distribution, the reduction in memory space required to store the dose kernel of individual pencil beams and the shortening of computation time for dose optimization and calculation. In this framework, the prediction of lateral dose distributions is a topic of great interest because currently, a Double Gaussian parametrization is typically used as approximation although other parameterizations are also available. The best accuracy for this kind of calculations can be obtained by Monte Carlo (MC) methods, at the expense of a long computing time. As alternative, we propose a flexible model based on the full Molière theory for Coulomb multiple scattering. The use of the original equations of the theory allows to remove free parameters for the electromagnetic inter action with the advantage of full accuracy with a reasonable increase in the computing time. The contribution of the nuclear interactions are also fully taken into account with a two-parameters fit on FLUKA simulation and this part is added to the electromagnetic core with a proper weight. The Model has been inserted in a research Treatment Planning System CERR - A Computational Environment for Radiotherapy Research, to compare its result against the ones obtained with the currently used Double Gaussian parametrization to evaluate the lateral energy deposition. A quantitative comparison has been done to evaluate the difference between a treatment plan obtained using the Double Gaussian parametrization and a treatment plan obtained using the model calculation, in the cases of a single beam and a full treatment plan in homogeneous water phantom and also a plan is performed in presence of inhomogeneities

Biological Impact of Target Fragments on Proton Treatment Plans: An Analysis Based on the Current Cross-Section Data and a Full Mixed Field Approach

SIMPLE SUMMARY: Proton therapy is now an established external radiotherapy modality for cancer treatment. Clinical routine currently neglects the radiobiological impact of nuclear target fragments even if experimental evidences show a significant enhancement in cell-killing effect due to secondary particles. This paper quantifies the contribution of proton target fragments of different charge in different irradiation scenarios and compares the computationally predicted corrections to the overall biological dose with experimental data. ABSTRACT: Clinical routine in proton therapy currently neglects the radiobiological impact of nuclear target fragments generated by proton beams. This is partially due to the difficult characterization of the irradiation field. The detection of low energetic fragments, secondary protons and fragments, is in fact challenging due to their very short range. However, considering their low residual energy and therefore high LET, the possible contribution of such heavy particles to the overall biological effect could be not negligible. In this context, we performed a systematic analysis aimed at an explicit assessment of the RBE (relative biological effectiveness, i.e., the ratio of photon to proton physical dose needed to achieve the same biological effect) contribution of target fragments in the biological dose calculations of proton fields. The TOPAS Monte Carlo code has been used to characterize the radiation field, i.e., for the scoring of primary protons and fragments in an exemplary water target. TRiP98, in combination with LEM IV RBE tables, was then employed to evaluate the RBE with a mixed field approach accounting for fragments’ contributions. The results were compared with that obtained by considering only primary protons for the pristine beam and spread out Bragg peak (SOBP) irradiations, in order to estimate the relative weight of target fragments to the overall RBE. A sensitivity analysis of the secondary particles production cross-sections to the biological dose has been also carried out in this study. Finally, our modeling approach was applied to the analysis of a selection of cell survival and RBE data extracted from published in vitro studies. Our results indicate that, for high energy proton beams, the main contribution to the biological effect due to the secondary particles can be attributed to secondary protons, while the contribution of heavier fragments is mainly due to helium. The impact of target fragments on the biological dose is maximized in the entrance channels and for small [Formula: see text] values. When applied to the description of survival data, model predictions including all fragments allowed better agreement to experimental data at high energies, while a minor effect was observed in the peak region. An improved description was also obtained when including the fragments’ contribution to describe RBE data. Overall, this analysis indicates that a minor contribution can be expected to the overall RBE resulting from target fragments. However, considering the fragmentation effects can improve the agreement with experimental data for high energy proton beams

The Drift Chamber detector of the FOOT experiment: Performance analysis and external calibration

The study that we present is part of the preparation work for the setup of the FOOT (FragmentatiOn Of Target) experiment whose main goal is the measurement of the double differential cross sections of fragments produced in nuclear interactions of particles with energies relevant for particle therapy. The present work is focused on the characterization of the gas-filled drift chamber detector composed of 36 sensitive cells, distributed over two perpendicular views. Each view consists of six consecutive and staggered layers with three cells per layer. We investigated the detector efficiency and we performed an external calibration of the space–time relations at the level of single cells. This information was then used to evaluate the drift chamber resolution. An external tracking system realized with microstrip silicon detectors was adopted to have a track measurement independent on the drift chamber. The characterization was performed with a proton beam at the energies of 228 and 80 MeV. The overall hit detection efficiency of the drift chamber has been found to be 0.929±0.008 , independent on the proton beam energy. The spatial resolution in the central part of the cell is about 150±10 μ m and 300±10 μ m and the corresponding detector angular resolution has been measured to be 1.62±0.16 mrad and 2.1±0.4 mrad for the higher and lower beam energies, respectively. In addition, the best value on the intrinsic drift chamber resolution has been evaluated to be in the range 60−100 μ m. In the framework of the FOOT experiment, the drift chamber will be adopted in the pre-target region, and will be exploited to measure the projectile direction and position, as well as for the identification of pre-target fragmentation events

Characterization of 150 μm\mu m thick silicon microstrip prototype for the FOOT experiment

International audienceThe goals of the FOOT (FragmentatiOn Of Target) experiment are to measure the proton double differential fragmentation cross-section on H, C, O targets at beam energies of interest for hadrontherapy (50–250 MeV for protons and 50–400 MeV/u for carbon ions), and also at higher energy, up to 1 GeV/u for radioprotection in space. Given the short range of the fragments, an inverse kinematic approach has been chosen, requiring precise tracking capabilities for charged particles. One of the subsystems designed for the experiment will be the MSD (Microstrip Silicon Detector), consisting of three x-y measurement planes, each one made by two single sided silicon microstrip sensors. In this document, we will present a detailed description of the first MSD prototype assembly, developed by INFN Perugia group and the subsequent characterization of the detector performance. The prototype is a wide area(∼ 100 cm$^{2}$) single sensor, 150 μm thick to reduce material budget and fragmentation probability along the beam path, with 50 μm strip pitch and 2 floating strip readout approach. The pitch adapter to connect strips with the readout channels of the ASIC has been implemented directly on the silicon surface. Beside the interest for the FOOT experiment, the results in terms of cluster signal, signal-to-noise ratio, dynamic range of the readout chips, as well as long-term stability studies in terms of noise, are relevant also for other experiments where the use of thin sensors is crucial

Characterization of 150 μm thick silicon microstrip prototype for the FOOT experiment

International audienceThe goals of the FOOT (FragmentatiOn Of Target) experiment are to measure the proton double differential fragmentation cross-section on H, C, O targets at beam energies of interest for hadrontherapy (50–250 MeV for protons and 50–400 MeV/u for carbon ions), and also at higher energy, up to 1 GeV/u for radioprotection in space. Given the short range of the fragments, an inverse kinematic approach has been chosen, requiring precise tracking capabilities for charged particles. One of the subsystems designed for the experiment will be the MSD (Microstrip Silicon Detector), consisting of three x-y measurement planes, each one made by two single sided silicon microstrip sensors. In this document, we will present a detailed description of the first MSD prototype assembly, developed by INFN Perugia group and the subsequent characterization of the detector performance. The prototype is a wide area(∼ 100 cm$^{2}$) single sensor, 150 μm thick to reduce material budget and fragmentation probability along the beam path, with 50 μm strip pitch and 2 floating strip readout approach. The pitch adapter to connect strips with the readout channels of the ASIC has been implemented directly on the silicon surface. Beside the interest for the FOOT experiment, the results in terms of cluster signal, signal-to-noise ratio, dynamic range of the readout chips, as well as long-term stability studies in terms of noise, are relevant also for other experiments where the use of thin sensors is crucial