Comparisons of dose distributions between IMPT and VMAT for pancreatic cancer / 中华放射医学与防护杂志

Objective:To compare dose distributions of hypofractionated radiotherapy for pancreatic cancer between IMPT and VMAT.Methods:Ten pancreatic cancer cases were included in this retrospective study. Photon (Edge) and proton (Proteus?PLUS) plans were designed by Eclipse and RayStation TPS, respectively. All plans were transferred to MIM system for extraction of parameters, which included Dmin, Dmean and Dmax of PTV, conformity index (CI), new conformity index (nCI), homogeneity index (HI), gradient index (GI), coverage, Dmax and dose-volume of the organs at risk (OARs). Results:There was no significant difference in CI between the two groups. The higher PTV Dmin, Dmean, Dmax, D98%, D2%, HI, coverage and the better GI, D2 cmwere found in VMAT ( t/ Z=-4.63-5.32, P<0.05). The lower 10%_PD was found in IMPT ( t=-7.47, P<0.05). Regarding the OARs, Dmax of the intestine, stomach, and duodenum and Dmean of the left kidney were similar between two groups without significant difference ( P>0.05). The D5 cm 3 of the intestine, D10 cm 3 of the stomach, D5 cm 3 and D10 cm 3 of the duodenum, D2/3 of the left kidney, Dmean and D2/3 of the right kidney were lower in IMPT than those in VMAT ( t/ Z=-8.12--2.60, P<0.05). However, the Dmax and D0.35 cm 3 of the spinal cord were higher in IMPT than those in VMAT ( t=7.30, 6.77, P<0.05). Conclusions:Both of hypofractionated radiotherapy plans of pancreatic cancer designed by VMAT and IMPT could meet clinical needs. No significant difference was found in Dmax of the adjacent gastrointestinal tracts between the two groups. While IMPT had the advantage over VMAT in the case of lower dose-volumes of the gastrointestinal tracts. Nevertheless, less protections of the OARs in front of the tumor volume could be provided by IMPT compared with VMAT.

Aplicación de un modelo de un acelerador Elekta Precise basado en Monte Carlo para la evaluación de la respuesta de detectores de estado sólido / Application of an Elekta Precise lineal accelerator model based on Monte Carlo to evaluate the solid state detectors response

En el trabajo se realizó el análisis de la respuesta de diferentes detectores de estado sólido a partir de un modelo de Monte Carlo de un acelerador lineal Elekta Precise, para los haces de energías de 6 MV y 15 MV. Para ello se realizaron simulaciones con el código EGSnrc. Se calculó la dosis depositada en un maniquí de agua voxelizado con su superficie a 100 cm de la fuente, empleando los valoresóptimos de energía media y FWHM del haz primario de electrones para este modelo. A partir de la dosis depositada en el maniquí se construyeron las curvas de dosis en profundidad y perfiles de dosis a diferentes profundidades. Las curvas se compararon con valores medidos para cada detector empleado en un arreglo experimental similar a la simulación realizada, aplicando criterios de aceptabilidad basados en intervalos de confianza. De forma adicional se analizó para cada caso la dosis en función del tamaño de campo. Se obtuvo una buena correspondencia entre las simulaciones y las mediciones, encontrándose todos los resultados dentro de los márgenes de tolerancia.

The evaluation of the solid state detectors response based on a Monte Carlo model of an Elekta Precise lineal accelerator, was done in this work for the beam energies of 6 y 15 MV. Simulations were performed using the EGSnrc code. Employing the optimal values of mean energy and FWHM from the primary electron beam, deposited dose in a voxelized water phantom at 100 cm of source to surface distance was calculated. Depth dose curves and lateral dose profi les were obtained. Comparison between simulations and the experimental values obtained for each detector, were done using acceptability criteria based on confi dence limits. Additionally outputs factors were analyzed in each one of the study cases. Good agreement between simulations and measurements were reached.

Nuevas curvas de calibración para la dosimetría biológica en Cuba / New calibration curves for biological dosimetry in Cuba

RESUMEN Se muestran 11 curvas dosis respuesta in vitro obtenidas por primera vez en el país para tres indicadores biológicos: anillos en cromosomas prematuramente condensados (PCC-R) índice PCC; focos gamma H2AX (-H2AX), todos ellos en linfocitos de sangre periférica humana. Estas curvas en su conjunto cubren un intervalo de dosis desde 0,1 Gy hasta 25 Gy, y varias calidades de radiación, así como varios tiempos post exposición, lo cual fortalece las capacidades para dar respuesta a las emergencias radiológicas y amplía las posibilidades de contribuir al esclarecimiento de cualquier suceso radiológico anormal que pueda ocurrir en la región, donde el indicador predominante en la actualidad continúa siendo la cuantificación de dicéntricos en linfocitos de la sangre periférica.

ABSTRACT In this paper we show the dose response curves in vitro obtained at first time in Cuba, with several biological indicators for radiation damage: rings in premature chromosome condensation (PCC-R); PCC index and -H2AX foci, all of these in peripheral human lymphocytes. These curves cover an interval of doses between 0.1 Gy to 25 Gy, several radiation qualities and times post-exposition, strengthening the capabilities of the Cuban laboratory to give answer to the radiological emergencies and in the same way increase its contribution to elucidate any radiological abnormal event take place at the region where the main indicator at the present time is the dicentric assay in lymphocytes of peripheral blood.

Design and optimization of a beam-shaping assembly for BNCT based on a neutron generator / Diseñó y optimización de un conformador del haz para terapia por captura de neutrones del boro, basado en un generador de neutrones

La simulación de un haz de neutrones se realizó para determinar la mejor energía de estos en el tratamiento de tumores bien profundos en la terapia por captura de neutrones del boro. Dos figuras de mérito, la máxima dosis absorbida en tejido sano y la dosis absorbida en el tumor a determinada profundidad dentro del cerebro, se utilizaron para evaluar la eficiencia del tratamiento. Se estudiaron el tiempo de irradiación, la ganancia terapéutica y la cantidad de potencia generada en el blanco, como parámetros de la calidad del haz. Se diseñaron y optimizaron moderadores, reflectores y delimitadores para moderar los neutrones de alta energía, producidos en la reacción de fusión (d;n), hasta un espectro de energías útiles para la terapia. Se utilizaron uranio metálico y manganeso para la moderación de neutrones rápidos a epitérmicos, mientras que el compuesto Fluental se utilizó para el ajuste final del espectro. Se propuso un blanco semiesférico para disipar el doble de la cantidad de potencia generada en el blanco, y disminuir las dimensiones del moderador. Todos los cálculos se realizaron utilizando el código de simulación MCNP-4C. Una vez obtenida la mejor configuración del moderador, se obtuvieron las distribuciones de dosis en la cabeza y el cerebro. La ganancia terapéutica se aumentó en un 9%, a la vez que la corriente requerida para una hora de tratamiento, así como las dimensiones del moderador disminuyeron en un 50%.

A monoenergetic neutron beam simulation study is carried out to determine the most suitable neutron energy for treatment of shallow and deep-seated brain tumors in the context of Boron Neutron Capture Therapy. Two figures-of-merit, i.e. the absorbed dose for healthy tissue and the absorbed tumor dose at a given depth in the brain are used to measure the neutron beam quality. Also irradiation time, therapeutic gain and the power generated in the target are utilized as beam assessment parameters. Moderators, reflectors and delimiters are designed and optimized to moderate the high-energy neutrons from the fusion reactions (d;n) and (d;n) down to a suitable energy spectrum. Metallic uranium and manganese are successfully tested for fast-to-epithermal neutron moderation as well as FluentalTM for the neutron spectrum shifting. A semispherical target is proposed in order to dissipate twice the amount of power generated in the target, and decrease all the dimensions of the BSA. The cooling system of the target is also included in the calculations. Calculations are performed using the MCNP code. After the optimization of our beam-shaper a study of the dose distribution in the head had been made. The therapeutic gain is increased in 9% while the current required for one hour treatment is decreased in comparison with the trading prototypes of NG used for Boron Neutron Capture Therapy.

Mass spectroscopy investigation of the effect of gamma irradiation on the mean value of the number of ethoxy groups in the triton x-100 / Estudio del efecto de la radiación gamma en elvalor medio del número de grupos etoxiLados del surfactante Tritón X-100

El efecto de la radiación gamma proveniente de una fuente de 60Co en la estructura del surfactante no iónico Tritón X-100 fue investigado. Tres regiones principales pueden ser distinguidas en el comportamiento del valor medio del número de grupos etóxidos al aumentar la dosis. Sin embargo, el resultado global encontrado fue una pequeña variación en este valor medio al cambiar la dosis entre 0 y 70 KGy.

The effect of gamma radiation from a 60Co source on the structure of a nonionic surfactant, namely TRITON X-100, was investigated. Three main regions can be distinguished in the behavior of the mean value of ethoxy groups with an increase in the absorbed dose. However just a slightly decrease on this mean value was obtained when the dose range from 0 to 70 kGy.

Dosimetric measurements for X(?)-knife beams / 中华放射肿瘤学杂志

Purpose: There is no appropriate instrument or devices and corresponding technological specification for measurement of output dose and dose disdribution in stereotactic radiothrapy. Small field of the stereotatic radiotherapy can't be measured by normal ionization chamber for its characteristics.A practible instrument and method were developed for dose measurement in stereotactic irradiation.Materials and Methods:A diode detector with 1mm sensitivety volume and a 0.3cc graphite chamber developed by us are used to measure the dose output & dose distribution in warious phantom for the beams used in stereotactic irradiation.Results:The dose outputs and dose ditributions measured by SCD-61 diode developed by us were tested and verified by TLD dosemeter,and the results show tha there is a 5% consistency for the value at the focus point.Conclusion: the diameter of the detector used for measurement must be smaller than the halt size of the radiation beams to be measured. A diode detector with 1mm sensitivity volume is the best choice for the dosimetric measurements for smaller beams used in stereotactic irradiation.

Optimization of Dose Distribution for LINAC-based Radiosurgery with Multiple Isocenters / 대한치료방사선과학회지

The current LINAC technique for radiosurgery utilizes a single isocenter approach with multiple noncoplanar arcs. This approach results in spherical dose distributions in the target. Many arteriovenous malformations and tumors suitable for radiosurgical treatment have non-spherical or irregular shapes. The basic approach presented in this paper is to use two or multiple isocenters with standard arcs to shape irregular target volumes through the use of multiple spherical targets. Selection of reasonable irradiation parameters in the first stage is critical to the success of real-time optimization. A useful guideline for optimum isocenter separation and collimator size is developed to shape the target margin uniformly with an desired isodose surface for an elongated target. The implementation of multiple isocenters with three dimensional dose model and application of multiple isocenters approach to several cases are discussed.