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[en] The measured lateral profiles (LP) by small ion chambers (IC) and the planar integral spot dose (PISD) by large area IC can be affected by their sizes and both need to be corrected. The purpose of this study is to: (a) quantify the detector size effect on the LP of the proton pencil beam spots (PPBS) and (b) to devise a procedure to accurately determine the PISD
[en] This paper presents the results-obtained in studying the two-prong interactions observed in the Saclay 81 cm hydrogen bubble chamber exposed to the 3.0 and 4.0 GeV/c antiproton beams from CERN Proton-Synchroton. Total elastic cross-sections corresponding to both energies are given. The results are given. The results are compared with those of p-p scaterring at different energies and with those of p-p scattering. Several optical-models, from the simples one (the black disk model) to a rather elaborated, four-parameters model have been applied. These models can explain some of the experimental results but fail in predicting the angular distribution of large angle scattering. (Author)
[en] Proton radiotherapy or proton therapy (PT) is based on the use of accelerated proton beams up to 230 MeV kinetic energies, to irradiate tumours very precisely. Although the proton therapy is coming to Spain now, with a center planned for the current year 2019 and a second for the year 2020, it is a totally contrasted cancer therapy, in continuous evolution and improvement, with more than sixty years of existence , and more than 90 centers in operation around the world. Proton therapy offers significant advantages in the treatment of certain types of tumours and clinical cases, and completes and extends existing therapies. The new centers in Spain will represent an important alternative for many patients who can benefit from the dosimetric characteristics of proton therapy. From the point of view of radioprotection, the facilities of protonterapia are radioactive facilities of second category, Type III, so its construction and operation must verify the Spanish regulations and accomplish the requeriments of the Nuclear Safety Council, and its shielding must be designed, executed and verified in accordance with the legal rules.
[es]La radioterapia con protones o protonterapia (PT) se basa en la utilización de haces de protones acelerados hasta energías cinéticas de 230 MeV, para irradiar tumores de forma muy precisa. Aunque la protonterapia está llegando a España ahora, con un centro previsto para el presente año 2019 y un segundo para el año 2020, se trata de una terapia contra el cáncer totalmente contrastada, en continua evolución y mejora, con más de sesenta años de existencia, y más de 90 centros en funcionamiento alrededor del mundo. La protonterapia ofrece ventajas significativas en el tratamiento de ciertos tipos de tumores y casos clínicos, completando y ampliando terapias existentes en la actualidad. Los nuevos centros en España van a suponer una alternativa importante para muchos pacientes que puedan beneficiarse de las características dosimétricas de este tipo de terapia. Desde el punto de vista de radioprotección, las instalaciones de protonterapia son instalaciones radiactivas de segunda categoría, Tipo III, por lo que su construcción y explotación deben verificar la reglamentación española y cumplir requerimientos del Consejo de Seguridad Nuclear, y su blindaje debe ser diseñado, ejecutado y verificado de acuerdo con dichas disposiciones.
[en] In spite of many experimental investigations, the energy dependence of the W value, defined as the mean energy required to produce an ion pair, is not yet well understood for protons and heavier charged particles. To clear up the energy dependence of the W value, it is calculated for protons in different gases employing an analytical model. In this model, the differential value ω is computed by using experimental data for the stopping power, the cross sections for the ionisation and the charge exchange, and the energy distribution of the ejected electrons that can produce additional ion pairs by ionisation of the target molecules. The model was used for protons of energy T between 0.1 and 1000 keV. Preliminary results suggest that the minimum in the W(T) curve can be attributed to the charge exchange of the ion projectiles with the gas molecules. (Author)
[en] Inverse planning for intensity- and energy-modulated radiotherapy (IEMRT) with proton beams involves the selection of (i) the relative importance factors to control the relative importance of the target and sensitive structures, (ii) an appropriate energy resolution to achieve an acceptable depth modulation, (iii) an appropriate beamlet width to modulate the beam laterally, and (iv) a sufficient number of beams and their orientations. In this article we investigate the influence of these variables on the optimized dose distribution of a simulated prostate cancer IEMRT treatment. Good dose conformation for this prostate case was achieved using a constellation of I factors for the target, rectum, bladder, and normal tissues of 500, 50, 15, and 1, respectively. It was found that for an active beam delivery system, the energy resolution should be selected on the basis of the incident beams' energy spread (σE) and the appropriate energy resolution varied from 1 MeV at σE=0.0 to 5 MeV at σE=2.0 MeV. For a passive beam delivery system the value of the appropriate depth resolution for inverse planning may not be critical as long as the value chosen is at least equal to one-half the FWHM of the primary beam Bragg peak. Results indicate that the dose grid element dimension should be equal to or no less than 70% of the beamlet width. For this prostate case, we found that a maximum of three to four beam ports is required since there was no significant advantage to using a larger number of beams. However for a small number (≤4) of beams the selection of beam orientations, while having only a minor effect on target coverage, strongly influenced the sensitive structure sparing and normal tissue integral dose
[en] A new protocol for calibration of proton beams was established by the ICRU in report 59 on proton dosimetry. In this paper we report the results of an international proton dosimetry intercomparison, which was held at Loma Linda University Medical Center. The goals of the intercomparison were, first, to estimate the level of consistency in absorbed dose delivered to patients if proton beams at various clinics were calibrated with the new ICRU protocol, and second, to evaluate the differences in absorbed dose determination due to differences in 60Co-based ionization chamber calibration factors. Eleven institutions participated in the intercomparison. Measurements were performed in a polystyrene phantom at a depth of 10.27 cm water equivalent thickness in a 6-cm modulated proton beam with an accelerator energy of 155 MeV and an incident energy of approximately 135 MeV. Most participants used ionization chambers calibrated in terms of exposure or air kerma. Four ionization chambers had 60Co-based calibration in terms of absorbed dose-to-water. Two chambers were calibrated in a 60Co beam at the NIST both in terms of air kerma and absorbed dose-to-water to provide a comparison of ionization chambers with different calibrations. The intercomparison showed that use of the ICRU report 59 protocol would result in absorbed doses being delivered to patients at their participating institutions to within ±0.9% (one standard deviation). The maximum difference between doses determined by the participants was found to be 2.9%. Differences between proton doses derived from the measurements with ionization chambers with NK-, or Nw - calibration type depended on chamber type. Using ionization chambers with 60Co calibration factors traceable to standard laboratories and the ICRU report 59 protocol, a distribution of stated proton absorbed dose is achieved with a difference less than 3%. The ICRU protocol should be adopted for clinical proton beam calibration. A comparison of proton doses derived from measurements with different chambers indicates that the difference in results cannot be explained only by differences in 60Co calibration factors. (author.)
[en] It is demonstrated that a dosimeter that consists of four ion chambers, each with different wall thickness, is able to reproduce the BFO dose with reasonable accuracy. This generalized dosimetric system is only slightly more complex than dosimeters in current use. This preliminary development had two built-in assumptions; the isotropicity of the radiation and the neglect of nuclear reaction effects. Only the nuclear reaction effects have been calculated. (U.S.)