1,721,185 research outputs found
The many faces of mathematical modelling in oncology
No full textThe application of modelling to solve problems in biology and medicine, and specifically in oncology and radiation therapy, is increasingly established and holds big promise. We provide an overview of the basic concepts of the field and its current state, along with new tools available and future directions for research. We will outline radiobiology models, examples of other anticancer therapy models, multiscale modelling, and we will discuss mechanistic and phenomenological approaches to modelling
Analisi e stima del contenuto di vapor d’acqua in atmosfera prodotta attraverso misure GNSS
No full textIl presente lavoro descrive le attività svolte nell'ambito del progetto "Sistema di monitoraggio in tempo reale dell'atmosfera per il Sardinia Radio Telescope (SRT)" finanziato con la Legge Regionale N.7 del 2007 della Sardegna. Sono esposte le attività svolte per il completamento dell’infrastruttura per il monitoraggio dell'atmosfera basata su stazioni permanenti GNSS appartenenti alla rete NRTK SARNET. Il completamento ha comportato l’installazione di un radiometro (MP3000A) nel sito di SRT e l’integrazione nella rete SARNET di 5 centraline meteorologiche (Vaisala PTU300) co-locate con altrettante stazioni permanenti della rete GNSS, a copertura della Sardegna meridionale. Si presentano, inoltre, le analisi effettuate sulle stime del contenuto di vapore d'acqua (IWV) derivate dal software GPSNet della Trimble, utilizzato nel centro di controllo della rete. Lo studio ha riguardato il confronto tra i valori del contenuto di vapor d’acqua in atmosfera misurati dal radiometro di SRT con quelli derivati dai ritardi troposferici ottenuti in tempo reale dalla rete GNSS in corrispondenza delle stazioni e successivamente interpolati in SRT. Nell'ambito dello stesso studio è stato possibile testare il nuovo software Trimble Atmosphere App, attualmente implementato parallelamente al software GPSNet sulla rete SARNET, in grado di fornire in tempo reale le mappe di IWV e del contenuto totale di elettroni (TEC)
Quantifying effects of lead shielding in electron beams: A Monte Carlo study
No full textLead shielding in contact with the patient's skin is often encountered in radiotherapy with electron beams. The influence of the lead shielding on dose distributions in the patient cannot fully be assessed using modern treatment planning systems. In this work the problem of quantifying the effect of lead shielding on dose distributions is addressed. Monte Carlo dose calculations were performed in a half-blocked water phantom shielded by lead, using a realistic model for the fluence of an electron linear accelerator. Electron beam energies of 6-20 MeV and lead thicknesses of 1-7 mm are used for 10 × 10 cm2 and 5 × 5 cm2 fields. The perturbation of the particle fluence and dose distributions in water introduced by the lead shielding is quantified. The effect of oblique electron beams on the dose perturbation is shown. A fictitious clinical example, the shielding of an eye in electron beam treatment, is used to demonstrate the usefulness of Monte Carlo based treatment planning algorithms that can incorporate the effects of lead shielding
Comparative analysis of dose volume histogram reduction algorithms for normal tissue complication probability calculations
No full textA model for estimating radiotherapy treatment outcome through the probability of damage to normal tissue and the probability of tumour control is a useful tool for treatment plan optimization, dose escalation strategies and other currently used procedures in radiation oncology. Normal tissue complication estimation (NTCP) is here analysed from the point of view of the reliability and internal consistency of the most popular model. Five different dose volume histogram (DVH) reduction algorithms, applied to the Lyman model for NTCP calculation, were analysed and compared. The study was carried out for sets of parameters corresponding to quite different expected dose-response relationships. In particular, we discussed the dependence of the models on the parameters and on the dose bin size in the DVH. The sensitivity of the different reduction schemes to dose inhomogeneities was analysed, using a set of simple DVHs representing typical situations of radiation therapy routine. Significant differences were substantiated between the various reduction methods regarding the sensitivity to the degree of irradiation homogeneity, to the model parameters and to the close bin size. Structural aspects of the reduction formalism allowed an explanation for these differences. This work shows that DVH reduction for NTCP calculation has still to be considered as avery delicate field and used with extreme care, especially for clinical applications, at least until the actual formulations are tuned against strong clinical data
Monte Carlo dose calculations and radiobiological modelling: Analysis of the effect of the statistical noise of the dose distribution on the probability of tumour control
No full textThe aim of this work is to investigate the influence of the statistical fluctuations of Monte Carlo (MC) dose distributions on the dose volume histograms (DVHs) and radiobiological models, in particular the Poisson model for tumour control probability (tcp). The MC matrix is characterized by a mean dose in each scoring voxel, d, and a statistical error on the mean dose, σ(d); whilst the quantities d and σ(d) depend on many statistical and physical parameters, here we consider only their dependence on the phantom voxel size and the number of histories from the radiation source. Dose distributions from high-energy photon beams have been analysed. It has been found that the DVH broadens when increasing the statistical noise of the dose distribution, and the tcp calculation systematically underestimates the real tumour control value, defined here as the value of tumour control when the statistical error of the dose distribution tends to zero. When increasing the number of energy deposition events, either by increasing the voxel dimensions or increasing the number of histories from the source, the DVH broadening decreases and tcp converges to the 'correct' value. It is shown that the underestimation of the tcp due to the noise in the dose distribution depends on the degree of heterogeneity of the radiobiological parameters over the population; in particular this error decreases with increasing the biological heterogeneity, whereas it becomes significant in the hypothesis of a radiosensitivity assay for single patients, or for subgroups of patients. It has been found, for example, that when the voxel dimension is changed from a cube with sides of 0.5 cm to a cube with sides of 0.25 cm (with a fixed number of histories of 108 from the source), the systematic error in the tcp calculation is about 75% in the homogeneous hypothesis, and it decreases to a minimum value of about 15% in a case of high radiobiological heterogeneity. The possibility of using the error on the tcp to decide how many histories to run for a given voxel size is also discussed
Dosimetric features of linac head and phantom scattered radiation outside the clinical photon beam: experimental measurements and comparison with treatment planning system calculations.
No full textBACKGROUND AND PURPOSE: Dosimetric measurements and treatment planning system (TPS) calculations in the region outside the clinical photon beams have been investigated. The aim was to estimate the calculation accuracy of a specific TPS in areas that are becoming increasingly relevant with the advent of new technologies, such as, for example, intensity modulation radiation therapy. MATERIALS AND METHODS: Measurements were performed on two different linacs to obtain, separately, the head scatter (electrons and photons), the transmission below the jaws and the phantom scatter outside the primary beam for different photon energies, distances from the field edge and field sizes. Calculations with a commercial TPS (Helax TMS) were then obtained and compared with these measurements. RESULTS: In general, reasonable agreement between calculations and measurements was obtained (1-2%), especially for photon scattering (head and phantom). Nevertheless, some discrepancies were found in the electron contamination computation, due probably to the approximations and assumptions made in the TPS calculation algorithm. CONCLUSIONS: The analyzed TPS presented good results, but for some particular clinical cases and moreover for advanced techniques such as intensity modulated radiation therapy, the calculation behaviour with respect to measurements and patient dose delivery should be carefully evaluated
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