Results 1 - 10 of 30443
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[en] The concept and general layout of a new high-power proton multistage (asynchronous) cyclotron is presented. The proposed cyclotron system has a number of advantages over the conventional one and may be simultaneously used for different purposes, particularly it can serve as a powerful proton driver in several applications of the Accelerator Driven Transmutation Technologies and also serve as a proton cancer therapy source, an isotopes processing source, etc. The possibility of fitting a four-stages cyclotron which is able to produce 1.0 GeV, 30 m A average-current protons, into the plant facilities of the existing 6-GeV Yerevan Electron Synchrotron is described. 6 refs
[en] In this work, results are presented for the measurements of convoy electrons Y (Vp) in function of velocity Vp of the emerging protons of the surface in the energy range.4 < Vp/Vo < 3.5. Measurements were performed in carbon films (5μg/cm2), aluminium (180A) and gold (150A) using coaxial cylindric spectrometer. (A.C.A.S.)
[pt]Apresenta-se os resultados para medicoes de 'convoy' eletrons Y (Vp) em funcao da velocidade Vp dos protons emergentes da superficie na faixa de energia 4< Vp/Vo < 3,5. As medicoes foram realizadas com laminas de carbono (5μg/cm2), aluminio (180A) e ouro (150A) usando um espectrometro coaxial cilindrico. (C.G.C.)
[en] In clinical proton beam radiation therapy, an RBE of 1.1 relative to megavoltage X-rays is currently being employed at most treatment centers. This RBE pertains to radiation in the spread out Bragg-peak (SOBP) for all tissue systems, all dose levels per fraction and all proton beam energies. As the number of centers and treatment sites for which proton beam therapy continues to increase and additional experimental data is accrued, a re-assessment of the justification for a generic RBE is warranted. In this paper we address: (1) the constancy of the RBE along the central axis from the plateau entrance to the distal SOBP (upstream of the distal edge); (2) RBE as a function of dose (or cell survival level); and (3) the target cell or tissue (α/β) dependency of the RBE. This analysis pertains to modulated proton beams of initial energies of approximately 70-200 MeV and SOBPs of approximately 2-10 cm, respectively. With exceptions, the available experimental data indicate that the RBE of SOBP protons increases with decreasing dose or dose per fraction and increasing depth in the SOBP. with the magnitude of both effects likely being dependent on the α/β ratios of the target cells or tissues. The use of a generic RBE of 1.1 for all tissues, especially those exhibiting low α/β values such as CNS, may be too low. especially at dose levels of ≤ 2 Gy/fraction. Systematic determination of the RBE values dependent upon the three interdependent variables identified in this manuscript (beam depth, dose size and target tissue) will provide an enhanced data base for detailed treatment planning and institutional trial comparisons, thereby maximizing the therapeutic benefit of proton beams. (author)
[en] Purpose: To investigate the safety and efficacy of proton beam therapy (PBT) in patients with large hepatocellular carcinoma (HCC). Methods and Materials: Twenty-two patients with HCC larger than 10 cm were treated with proton beam therapy at our institution between 1985 and 2006. Twenty-one of the 22 patients were not surgical candidates because of advanced HCC, intercurrent disease, or old age. Median tumor size was 11 cm (range, 10-14cm), and median clinical target volume was 567 cm3 (range, 335-1,398 cm3). Hepatocellular carcinoma was solitary in 18 patients and multifocal in 4 patients. Tumor types were nodular and diffuse in 18 and 4 patients, respectively. Portal vein tumor thrombosis was present in 11 patients. Median total dose delivered was 72.6 GyE in 22 fractions (range, 47.3-89.1 GyE in 10-35 fractions). Results: The median follow-up period was 13.4 months (range, 1.5-85 months). Tumor control rate at 2 years was 87%. One-year overall and progression-free survival rates were 64% and 62%, respectively. Two-year overall and progression-free survival rates were 36% and 24%, respectively. The predominant tumor progression pattern was new hepatic tumor development outside the irradiated field. No late treatment-related toxicity of Grade 3 or higher was observed. Conclusions: The Bragg peak properties of PBT allow for improved conformality of the treatment field. As such, large tumor volumes can be irradiated to high doses without significant dose exposure to surrounding normal tissue. Proton beam therapy therefore represents a promising modality for the treatment of large-volume HCC. Our study shows that PBT is an effective and safe method for the treatment of patients with large HCC.