Spectrum averaged cross section measurements of lutetium using standard 252Cf neutron source.

The spectrum averaged cross section (SACS) in a standard neutron field is a preferable tool for cross section validation. The presented work uses only neutron standard, i.e., 252Cf(sf) reaction neutron field, for validation of lutetium threshold cross sections. SACS were inferred from gamma spectrometry derived reaction rates. The SACS which were derived include 175Lu (n,2n)174Lu, 175Lu (n,3n)173Lu, 175Lu (n,p)175Yb, and 176Lu (n,n')176m1Lu reactions. All these reactions SACS were measured for the first time. MCNP6.2 calculations using JEFF-3.3 or ENDF/B-VIII.0 libraries for lutetium cross sections were compared with experimental data. The agreement was found very poor for all reactions under study. Thus there is a need for their improvement. The presented data can be also used for validation of the various theoretical models.

Testing of various neutron filters in reference neutron field in LR-0 reactor for nuclear data validation and verification.

Neutron activation analysis is the reference method used for offline determination of the neutron flux density in defined positions. It can be used in the nuclear energy industry-as well as in medical- or space applications. For accurate neutron flux evaluation, well-known and reliable cross sections are needed. In the thermal and fast energy region, many reliable monitoring reactions exists, however, in case of the epithermal and intermediate energy region, there are practically no dosimetry nuclear reactions sensitive specifically in this energy range. Due to this fact, both new data are being measured and methodologies are under development to describe and test this energy region. It was found that various neutron filters can be used to cut parts of neutron spectra and thus methodology based on spectrum filtering could potentially be employed to survey cross sections of interest. It this paper, the use of 3 different filters - B4C, Cd, and In is studied, on the case of the 55Mn(n,γ) reaction. Measured values of that cross section in the given filtered reference spectra are reported.

Validation of selected (n,2n) dosimetry reactions in IRDFF-1.05 library.

Spectrum-averaged cross sections (SACS) have been measured in the reference 252Cf(sf) neutron field for the following high-threshold (n,2n) neutron dosimetry reactions since they are especially important due to the high threshold which allows validation of upper parts of prompt fission neutron spectrum. This work includes 59Co(n,2n)58Co, 197Au(n,2n)196Au, 169Tm(n,2n)168Tm, 55Mn(n,2n)54Mn, 93Nb(n,2n)92 mNb and 89Y(n,2n)88Y and for the 59Co(n,p)59Fe threshold reactions. SACS were inferred from experimentally determined reaction rates by gamma spectrometry using a semiconductor high-purity germanium detector to measure irradiated samples. Measured reaction rates agree within quoted uncertainties with those calculated from the IRDFF-1.05 library, except for the reaction 55Mn(n,2n)54Mn, for which the measured value is underestimated by 16%. For this reaction the ENDF-B/VII.1 evaluation agrees with measured reaction rate within uncertainties.

An implementation to read and write IAEA phase-space files in GEANT4-based simulations.

PURPOSE: To develop a stand-alone code to make any application coded with the GEANT4 (GEometry ANd Tracking, version 4) toolkit capable of reading and writing phase-space (phsp) files in the format created by the IAEA (International Atomic Energy Agency), so that the exchange of phsp files between other validated Monte Carlo (MC) codes and GEANT4 is possible. METHODS: We present a stand-alone code, written in C++ object-oriented language, developed in a way that ensures the compatibility with future versions of the IAEA phsp format. The aim of the reader part is to get the information from a given IAEA phsp file and create the primary particles in a GEANT4 user application. On the other hand, the writer part of the code is the responsible for writing the IAEA phsp files during a run of the GEANT4 application. RESULTS: A testing simulation was written with GEANT4 to verify the performance of this code, with satisfactory results. An example of use in a GEANT4 application which simulates the treatment head of a radiotherapy linear electron accelerator (linac) is also shown, comparing dose calculations with experimental data. CONCLUSIONS: This stand-alone package, which can be used in any GEANT4 application, allows the exchange of validated phsp files between different MC codes and the use of phsp data from many different accelerators and fields in dosimetry studies. Furthermore, it also offers additional utilities of interest in medical applications.

Production of 230U/226Th for targeted alpha therapy via proton irradiation of 231Pa.

(230)U and its daughter nuclide (226)Th are novel therapeutic nuclides for application in targeted alpha-therapy of cancer. We have investigated the feasibility of producing (230)U/(226)Th via proton irradiation of (231)Pa according to the reaction (231)Pa(p,2n)(230)U. The experimental excitation function for this reaction is reported for the first time. Cross sections were measured using thin targets of (231)Pa prepared by electrodeposition and (230)U yields were analyzed using alpha-spectrometry. Beam parameters (energy and intensity) were determined both by calculation using a mathematical model based on measured beam orbits and beam current integrator and by parallel monitor reactions on copper foils using high-resolution gamma-spectrometry and IAEA recommended cross-section data. The measured cross sections are in good agreement with model calculations using the EMPIRE-II code and are sufficiently high for the production of (230)U/(226)Th in clinically relevant amounts. A highly effective separation process was developed to isolate clinical grade (230)U from irradiated protactinium oxide targets. Product purity was assessed using alpha- and gamma-spectrometry as well as ICPMS.

Cross-sections of the reaction 232Th(p,3n)230Pa for production of 230U for targeted alpha therapy.

(230)U/(226)Th is a promising novel alpha-emitter system for application in targeted alpha therapy of cancer. The therapeutic nuclides can be produced by proton irradiation of natural (232)Th according to the reaction (232)Th(p,3n)(230)Pa, followed by subsequent beta decay of (230)Pa to (230)U. In this study, the experimental excitation function for the (232)Th(p,3n)(230)Pa reaction up to 34 MeV proton energy has been measured using the stacked-foil technique. The proton energies in the various foils were calculated with the SRIM 2003 code and gamma-ray spectrometry was used to measure the activities of the various radioisotopes produced. The measured cross-sections are in good agreement with selected literature values and with model calculations using the EMPIRE II code. The reaction (232)Th(p,3n)(230)Pa allows the production of carrier-free (230)U in clinically relevant levels.

Uncertainty estimation in intensity-modulated radiotherapy absolute dosimetry verification.

PURPOSE: Intensity-modulated radiotherapy (IMRT) represents an important method for improving RT. The IMRT relative dosimetry checks are well established; however, open questions remain in reference dosimetry with ionization chambers (ICs). The main problem is the departure of the measurement conditions from the reference ones; thus, additional uncertainty is introduced into the dose determination. The goal of this study was to assess this effect systematically. METHODS AND MATERIALS: Monte Carlo calculations and dosimetric measurements with five different detectors were performed for a number of representative IMRT cases, covering both step-and-shoot and dynamic delivery. RESULTS: Using ICs with volumes of about 0.125 cm(3) or less, good agreement was observed among the detectors in most of the situations studied. These results also agreed well with the Monte Carlo-calculated nonreference correction factors (c factors). Additionally, we found a general correlation between the IC position relative to a segment and the derived correction factor c, which can be used to estimate the expected overall uncertainty of the treatment. CONCLUSION: The increase of the reference dose relative standard uncertainty measured with ICs introduced by nonreference conditions when verifying an entire IMRT plan is about 1-1.5%, provided that appropriate small-volume chambers are used. The overall standard uncertainty of the measured IMRT dose amounts to about 2.3%, including the 0.5% of reproducibility and 1.5% of uncertainty associated with the beam calibration factor. Solid state detectors and large-volume chambers are not well suited to IMRT verification dosimetry because of the greater uncertainties. An action level of 5% is appropriate for IMRT verification. Greater discrepancies should lead to a review of the dosimetric procedure, including visual inspection of treatment segments and energy fluence.

Micro ionization chamber dosimetry in IMRT verification: clinical implications of dosimetric errors in the PTV.

BACKGROUND AND PURPOSE: Absolute dose measurements for Intensity Modulated Radiotherapy (IMRT) beamlets is difficult due to the lack of lateral electron equilibrium. Recently we found that the absolute dosimetry in the penumbra region of the IMRT beamlet, can suffer from significant errors (Capote et al., Med Phys 31 (2004) 2416-2422). This work has the goal to estimate the error made when measuring the Planning Target Volume's (PTV) absolute dose by a micro ion chamber (microIC) in typical IMRT treatment. The dose error comes from the assumption that the dosimetric parameters determining the absolute dose are the same as for the reference conditions. MATERIALS AND METHODS: Two IMRT treatment plans for common prostate carcinoma case, derived by forward and inverse optimisation, were considered. Detailed geometrical simulation of the microIC and the dose verification set-up was performed. The Monte Carlo (MC) simulation allows us to calculate the delivered dose to water and the dose delivered to the active volume of the ion chamber. However, the measured dose in water is usually derived from chamber readings assuming reference conditions. The MC simulation provides needed correction factors for ion chamber dosimetry in non reference conditions. RESULTS: Dose calculations were carried out for some representative beamlets, a combination of segments and for the delivered IMRT treatments. We observe that the largest dose errors (i.e. the largest correction factors) correspond to the smaller contribution of the corresponding IMRT beamlets to the total dose delivered in the ionization chamber within PTV. CONCLUSION: The clinical impact of the calculated dose error in PTV measured dose was found to be negligible for studied IMRT treatments.

Microionization chamber for reference dosimetry in IMRT verification: clinical implications on OAR dosimetric errors.

Intensity modulated radiotherapy (IMRT) has become a treatment of choice in many oncological institutions. Small fields or beamlets with sizes of 1 to 5 cm2 are now routinely used in IMRT delivery. Therefore small ionization chambers (IC) with sensitive volumes 0.1 cm3 are generally used for dose verification of an IMRT treatment. The measurement conditions during verification may be quite different from reference conditions normally encountered in clinical beam calibration, so dosimetry of these narrow photon beams pertains to the so-called non-reference conditions for beam calibration. This work aims at estimating the error made when measuring the organ at risk's (OAR) absolute dose by a micro ion chamber (microIC) in a typical IMRT treatment. The dose error comes from the assumption that the dosimetric parameters determining the absolute dose are the same as for the reference conditions. We have selected two clinical cases, treated by IMRT, for our dose error evaluations. Detailed geometrical simulation of the microIC and the dose verification set-up was performed. The Monte Carlo (MC) simulation allows us to calculate the dose measured by the chamber as a dose averaged over the air cavity within the ion-chamber active volume (D(air)). The absorbed dose to water (D(water)) is derived as the dose deposited inside the same volume, in the same geometrical position, filled and surrounded by water in the absence of the ion chamber. Therefore, the D(water)/D(air) dose ratio is the MC estimator of the total correction factor needed to convert the absorbed dose in air into the absorbed dose in water. The dose ratio was calculated for the microIC located at the isocentre within the OARs for both clinical cases. The clinical impact of the calculated dose error was found to be negligible for the studied IMRT treatments.

An EGSnrc Monte Carlo study of the microionization chamber for reference dosimetry of narrow irregular IMRT beamlets.

Intensity modulated radiation therapy (IMRT) has evolved toward the use of many small radiation fields, or "beamlets," to increase the resolution of the intensity map. The size of smaller beamlets can be typically about 1-5 cm2. Therefore small ionization chambers (IC) with sensitive volumes < or = 0.1 cm3 are generally used for dose verification of IMRT treatment. The dosimetry of these narrow photon beams pertains to the so-called nonreference conditions for beam calibration. The use of ion chambers for such narrow beams remains questionable due to the lack of electron equilibrium in most of the field. The present contribution aims to estimate, by the Monte Carlo (MC) method, the total correction needed to convert the IBA-Wellhöfer NAC007 micro IC measured charge in such radiation field to the absolute dose to water. Detailed geometrical simulation of the microionization chamber was performed. The ion chamber was always positioned at a 10 cm depth in water, parallel to the beam axis. The delivered doses to air and water cavity were calculated using the CAVRZ EGSnrc user code. The 6 MV phase-spaces for Primus Clinac (Siemens) used as an input to the CAVRZnrc code were derived by BEAM/EGS4 modeling of the treatment head of the machine along with the multileaf collimator [Sánchez-Doblado et al., Phys. Med. Biol. 48, 2081-2099 (2003)] and contrasted with experimental measurements. Dose calculations were carried out for two irradiation geometries, namely, the reference 10x10 cm2 field and an irregular (approximately 2x2 cm2) IMRT beamlet. The dose measured by the ion chamber is estimated by MC simulation as a dose averaged over the air cavity inside the ion-chamber (Dair). The absorbed dose to water is derived as the dose deposited inside the same volume, in the same geometrical position, filled and surrounded by water (Dwater) in the absence of the ionization chamber. Therefore, the Dwater/Dair dose ratio is a MC direct estimation of the total correction factor needed to convert the absorbed dose in air to absorbed dose to water. The dose ratio was calculated for several chamber positions, starting from the penumbra region around the beamlet along the two diagonals crossing the radiation field. For this quantity from 0 up to a 3% difference is observed between the dose ratio values obtained within the small irregular IMRT beamlet in comparison with the dose ratio derived for the reference 10x10 cm2 field. Greater differences from the reference value up to 9% were obtained in the penumbra region of the small IMRT beamlet.

MLC leaf width impact on the clinical dose distribution: a Monte Carlo approach.

PURPOSE: The influence of the multileaf collimator (MLC) leaf width on the dose distribution in patients treated with conformal radiotherapy and intensity-modulated radiotherapy has been analyzed. This study was based on the Monte Carlo simulation with the beams generated by a linac with the double-focused MLC. MATERIALS AND METHODS: The transmission through the leaves and the exact shape of the penumbra regions are difficult to model by treatment planning system algorithms. An accurate assessment of the dose variations due to the leaf width change can be achieved by means of Monte Carlo simulation. The BEAM/EGS4 code was used at the Hospital of the Virgen Macarena to model a Siemens PRIMUS linac, featuring an MLC with a leaf width projecting 1 cm at the isocenter. Based on this real model, a virtual head was designed while allowing for a variation of the leaf width projection. Both the real linac and the virtual linac, with leaves projecting 0.5 cm, were used to obtain the dose distributions for several treatments. A few disease sites, including the prostate, head and neck, and endometrium, were selected for the design of the conformal and intensity-modulated radiotherapy treatments with a forward planning algorithm sensitive to the different shapes of the volumes of interest. Isodose curves, differential matrix, gamma function, and the dose-volume histograms (DVHs) corresponding to both MLC models were obtained for all cases. The tumor control probability and the normal tissue complication probability were derived for those cases studied featuring the greatest differences between results for both MLCs. RESULTS: The impact on the DVHs of changing leaf width projections at the isocenter from 1.0 cm to 0.5 cm was low. Radiobiologic models showed slightly better tumor control probability/normal tissue complication probability values using the virtual MLC with a leaf width projecting 0.5 cm at isocenter in those cases presenting greater differences in the DVHs. CONCLUSIONS: The impact on the clinical dose distribution due to the MLC leaf width change is low based on the design and conditions used in this study.

Total skin electron therapy treatment verification: Monte Carlo simulation and beam characteristics of large non-standard electron fields.

Total skin electron therapy (TSET) is a complex technique which requires non-standard measurements and dosimetric procedures. This paper investigates an essential first step towards TSET Monte Carlo (MC) verification. The non-standard 6 MeV 40 x 40 cm2 electron beam at a source to surface distance (SSD) of 100 cm as well as its horizontal projection behind a polymethylmethacrylate (PMMA) screen to SSD = 380 cm were evaluated. The EGS4 OMEGA-BEAM code package running on a Linux home made 47 PCs cluster was used for the MC simulations. Percentage depth-dose curves and profiles were calculated and measured experimentally for the 40 x 40 cm2 field at both SSD = 100 cm and patient surface SSD = 380 cm. The output factor (OF) between the reference 40 x 40 cm2 open field and its horizontal projection as TSET beam at SSD = 380 cm was also measured for comparison with MC results. The accuracy of the simulated beam was validated by the good agreement to within 2% between measured relative dose distributions, including the beam characteristic parameters (R50, R80, R100, Rp, E0) and the MC calculated results. The energy spectrum, fluence and angular distribution at different stages of the beam (at SSD = 100 cm, at SSD = 364.2 cm, behind the PMMA beam spoiler screen and at treatment surface SSD = 380 cm) were derived from MC simulations. Results showed a final decrease in mean energy of almost 56% from the exit window to the treatment surface. A broader angular distribution (FWHM of the angular distribution increased from 13 degrees at SSD = 100 cm to more than 30 degrees at the treatment surface) was fully attributable to the PMMA beam spoiler screen. OF calculations and measurements agreed to less than 1%. The effect of changing the electron energy cut-off from 0.7 MeV to 0.521 MeV and air density fluctuations in the bunker which could affect the MC results were shown to have a negligible impact on the beam fluence distributions. Results proved the applicability of using MC as a treatment verification tool for complex radiotherapy techniques.

Estudios de las técnicas de facilitación neuromuscular como medio para la disminución de la espasticidad en pacientes con lesiones estáticas encefálicas producidas por accidentes cerebrovasculares / Study of the tecnics of the neuromuscular facilitation how mean for to diminution of the spasticity in the patients with static encephalic lesions produced by brain-stroke

El estudio está dirigido a demonstrar que es posible disminuir los niveles de espasticidad de los pacientes que han sufrido Lesiones Estaticas Encefálicas producidas por Accidentes Cerebrovasculares, al aplicar un programa de neurorehabilitación donde se emplearon um grupo de Técnicas de Facilitación neuromuscular previamente seleccionadas.El experimento se realizó con una muestra de doze pacientes, seis pertencientes al grupo control y seis al grupo experimental, cuyo diagnóstico era el de accidentes cerebrovasculares que havían dejado como secuela hemiplejías de tipo espásticas. Todos ellos recibieron tratamiento en el Centro Internacional de Restauración Neurológica (CIREN). A los seis sujeitos del grupo no se les aplicaron las tecnicas de facilitación seleccionadas para el grupo experimental.El período de rehabilitación para los doce pacientes fue de un mes. La evaluación se llevó a cabo a través de mediciones goniométricas y la aplicación de la Escala Internacional de Barthel.Se comprobó que las tecnicas de facilitación neuromuscular utilizadas contribuyeron a disminuir considerablemente los niveles de espasticidad, existiendo diferencias significativas en el aumento de la amplitud articular del grupo experimental con respecto al grupo control, y se observó una tendencia mayor al aumento de la funcionalidad en el grupo experimental