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Introducción: La dupla Cyberknife y bisturí de rayos gamma (Infini) que se describe es la primera en Latinoamérica. Ambas máquinas han mostrado ser los mejores equipos para radiocirugía intracraneal. Se describe la experiencia inicial de Cyberknife en Centroamérica y su incorporación a un programa existente de bisturí de rayos gamma por vía de análisis comparativos dosimétricos. Material y método: En el año 2019 se realizaron planes comparativos y se trataron 180 pacientes con radiocirugía intracraneal con ambos sistemas tanto en patología tumoral, como vascular y funcional. Resultados: En el análisis dosimétrico comparativo en el gradiente de dosis de Infini mostró ser superior a Cyberknife en todos los casos. Para una esfera utilizando el colimador de 4 mm en Infini y de 5 mm en Cyberknife utilizando un plan isocéntrico con el -Trigeminal Path- el gradiente de dosis para Infini fue de 1.5 y para Cyberknife de 1.66. Para los casos de patología el gradiente de dosis media para Infini fue de 3 mm y para Cyberknife de 3.8 mm. Dando un puntaje de gradiente de dosis (Gradient Score Index) si Infini fuese de 100, Cyberknife obtuvo 87.3. Cyberknife mostró mejor conformalidad y cobertura (97% versus 96%) para todos los targets. Entre enero 2019 y enero 2020 se realizaron 180 radiocirugías, 60 con Cyberknife y 120 con Infini, 60 pacientes recibieron 146 sesiones con Cyberknife, radiocirugía fraccionada 39 (65%) y 21 (35%) en sesión única. Las dosis medias en tumores en dosis única fue 15 Gy (12.5 a 25 Gy) y en radiocirugía fraccionada 21 Gy (18 y 35). Ningún paciente ha experimentado toxicidad mayor a grado dos. Conclusiones: El bisturí de rayos gamma rotatorio reveló superioridad en gradiente de dosis con relación al Cyberknife. En su primer año Cyberknife ha mostrado ser una herramienta segura en el tratamiento de patología intracraneal. Más seguimiento clínico y radiológico es necesario para verificar su efectividad comparativa
Introduction: The match between Cyberknife and Infini here described in this article is the first in Latinamerica. Both machines have proven to be the best for intracranial radiosurgery, we describe our initial experience with Cyberknife in Central America and how it was incorporated in an existing gamma ray program by ways of dosimetry comparisons. Methods: During 2019 comparative plans were made and a total of 180 patients received intracranial radiosurgery with both technologies, patients were treated for tumors, vascular anomalies, and functional pathology. Results: Basic dosimetry analysis regarding dose gradient the Infini proved superior to Cyberknife in all plans. For a sphere using the 4 mm collimator in Infini and the 5 mm in Cyberknife along with an isocentric plan using the -Trigeminal Path- dose gradient was 1.5 for Infini and 1.66 for Cyberknife. For the pathology cases Infini was 3 mm and for Cyberknife 3.8 mm on mean. Giving a Gradient Score Index (GSI) if Infini would be 100, Cyberknife would be 87.3. Cyberknife showed better conformality and coverage for all pathology targets (97% versus 96%). From January 2019 to January 2020, 180 intracranial radiosurgeries were done, 60 with Cyberknife and 120 with Infini, 60 patients received 146 sessions with Cyberknife, fractionated scheme 39 (65%) and 21 (35%) single dose. The median dose for tumors was 15 Gy (12.5 a 25 Gy) for single session and 21 Gy (18 y 35) for fractionated scheme. No patient experienced a higher toxicity tan grade two. Conclusions: In its first year Cyberknife has shown to be safe in treating intracranial pathology. Infini had a better dose gradient than Cyberknife. Longer clinical and radiological follow-up is needed to verify its comparative effectiveness.
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Humanos , Radiocirurgia , Cérebro , Metástase Neoplásica , Neoplasias , NeurocirurgiaRESUMO
Introducción: Las recomendaciones en el manejo de metástasis superiores a 2 cm especialmente las sintomáticas sugieren cirugía como primera opción. En el presente artículo se discute el papel de radiocirugía como primer manejo de estos pacientes. Material y método: Se evaluaron 37 pacientes sintomáticos con lesiones metastásicas superiores a 8.5 cc tratados con radiocirugía entre el 2011 y el 2018. Resultados: La media de volumen fue de 12.5 cc (8.5-78.4), 9 (24%) pacientes fueron tratados utilizando LINAC, el volumen medio fue de 20 cc (9.2-70 cc). Los tratamientos con Gamma-Ray fueron administrados a 28 (76%) pacientes, 9 (32%) de ellos en protocolo de radiocirugía adaptativa, la dosis para todo el grupo fue de 13.8 Gy (7.5-18 Gy), con dosis media de 17.9 Gy, el volumen medio fue de 16.3 cc (8.5-78.4 cc) para gamma. El Karnofsky al inicio era de 60 (50-70) y de 80 (60-100) a los 30 días (P=0.0001). A los 30 días, 95% de las lesiones habían reducido su tamaño en un 74% (11-95%). La sobrevida media de la serie fue de 19 meses (4-34), el riesgo acumulado de muerte del SNC fue de 5.4%. Conclusiones: Radiocirugía en nuestra experiencia ha mostrado ser eficaz en el control de metástasis a cerebro de gran tamaño, reduciendo la necesidad de cirugí
Introduction: Current recommendations with regards to metastases larger than 2 cm specially in symptomatic patients suggest surgery as a first choice. We analyze the role of upfront radiosurgery as first line of treatment in such patients. Methods: 37 symptomatic patients that harbored tumors greater than 8.5 cc in volume were treated from 2011 to January 2018. Results: The median tumor volume was 12.5 cc (8.5-78.4), 9 (24%) patients were treated with LINAC with a volume of 20 cc (9.2-70 cc). The treatments with GammaRay were administrated to 28 (76%) patients, 9 (32%) of them with adaptive radiosurgery protocol, the prescription dose for the gamma group was 13.8 Gy (7.5-18Gy) mean dose of 17.9 Gy (13.2-23.3 Gy) with a mean volume of 16.3 cc (8.5-78.4 cc). Karnofsky score was 60 (50-70) the day of treatment and 80 (60-100) at 30 days (P=0.0001). At 30 days, 95% of the tumors had reduced in size in a 74% (11-95%) for those evaluated. Median survival was 19 months (4-34), with an accumulative risk of death from central nervous progression of 5.4%. Conclusions: Radiosurgery in our experience has shown to be effective in controlling large metastases, reducing the need for open surgery.
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Humanos , Feminino , Neoplasias da Mama , Sistema Nervoso Central , Radiocirurgia , Cérebro , Metástase Neoplásica , Neoplasias , NeurocirurgiaRESUMO
En el Departamento de Radioterapia del Instituto de Oncología y Radiobiología se ha puesto, en servicio clínico, un moderno acelerador lineal de electrones. Esto brindó la posibilidad de utilizar el dispositivo electrónico de imagen portal (EPID) para realizar los controles de calidad paciente-específico de tratamientos de radioterapia, con intensidad modulada (IMRT). Se estudió y validó el uso del EPID en la verificación de tratamientos de IMRT, modalidad de múltiples segmentos estáticos, con fotones de 6 MV de energía. Se determinó la curva dosis-respuesta del EPID para valores de dosis en agua. Se halló la profundidad de referencia en agua del EPID (Descripción: D:/Scielo/Nucleus html/n 59/img/e01055916.jpg) mediante la determinación de su respuesta a la variación del tamaño de campo, y la comparación de esta con la variación del factor de dispersión en agua, calculado para diferentes profundidades, con un sistema de planificación de tratamientos (TPS). Se calcularon perfiles y mapas de dosis a Descripción: D:/Scielo/Nucleus html/n 59/img/e01055916.jpg con el TPS, utilizando una configuración de haces colapsados. Los mapas de dosis y perfiles fueron comparados con los medidos, usando las imágenes procesadas del EPID para diferentes casos clínicos sencillos (campos abiertos y con cuña) y uno complejo (caso clínico de IMRT de cabeza y cuello). Se utilizó la función Gamma como herramienta de comparación. El criterio de comparación Gamma empleado fue 3 % de diferencia de dosis y 4 mm de distancia para la concordancia de la dosis. Se obtuvo una tasa de aceptación mayor del 90% para los puntos evaluados.
A modern clinical electron linear accelerator was commissioned at the Department of Radiotherapy in the Oncology and Radiobiology Institute. The use of electronic portal image device (EPID) for patient-specific intensity modulated radiotherapy (IMRT) quality assurance is assessed and validated. An IMRT step & shoot approach, using multileaf collimator was used. The EPID dose-response curve was determined for a 6MV photon beam. The EPID effective water scattering depth (Descripción: D:/Scielo/Nucleus html/n 59/img/e01055916.jpg) was assessed through measurements of its response versus field size variation and compared with the output factor scatter at different depths, calculated with a radiotherapy treatment planning system (TPS). Dose profiles and dose maps were calculated at Descripción: D:/Scielo/Nucleus html/n 59/img/e01055916.jpg with the TPS, using a collapsed beam setup. The dose maps and profiles were compared with the processed EPID images for simple cases (i.e. open and wedged fields) and a more complex case (a head and neck IMRT clinical case). Comparison was performed using the Gamma function. Results showed Gamma passing rates higher than 90 % for all compared points, using comparison criteria of dose difference 3% and 4mm of distance to agreement.
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Los análisis de riesgo aplicados a los tratamientos de radioterapia se han convertido en una necesidad innegable, partiendo de los peligros generados por la combinación del empleo de potentes campos de radiación sobre los pacientes y la ocurrencia de errores humanos y fallos de equipos durante esos tratamientos. La técnica por excelencia para llevar a cabo estos análisis ha sido la matriz de riesgo. El trabajo presenta el desarrollo de un nuevo algoritmo para ejecutar esta tarea con amplias potencialidades gráficas y analíticas, lo que lo convierte en una opción muy útil para el monitoreo del riesgo y la optimización de los programas de garantía de calidad. El sistema SECURE-MR, soporte informático de este algoritmo, se empleó con éxito en el análisis de riesgo de diversas prácticas de radioterapia. Lo distinguen nuevas posibilidades de análisis partiendo de la consideración de factores controladores del riesgo como las robusteces de frecuencia de iniciadores y de consecuencias. Sus capacidades analíticas y gráficas permiten novedosos desarrollos de ordenamiento de contribuyentes al riesgo y de representación de la información de procesos y secuencias accidentales. El trabajo muestra la aplicación del sistema propuesto a un proceso genérico de tratamiento de radioterapia con acelerador lineal.
Risk analyses applied to radiotherapy treatments have become an undeniable necessity, considering the dangers generated by the combination of using powerful radiation fields on patients and the occurrence of human errors and equipment failures during these treatments. The technique par excellence to execute these analyses has been the risk matrix. This paper presents the development of a new algorithm to execute the task with wide graphic and analytic potentialities, thus transforming it into a very useful option for risk monitoring and the optimization of quality assurance. The system SECURE-MR, which is the basic software of this algorithm, has been successfully used in risk analysis regarding different kinds of radiotherapies. Compared to previous methods, It offers new possibilities of analysis considering risk controlling factors as the robustness of reducers of initiators frequency and its consequences. Their analytic capacities and graphs allow novel developments to classify risk contributing factors, to represent information processes as well as accidental sequences. The paper shows the application of the proposed system to a generic process of radiotherapy treatment using a lineal accelerator.
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Simulation of a linear accelerator (linac) head requires determining the parameters that characterize the primary electron beam striking on the target which is a step that plays a vital role in the accuracy of Monte Carlo calculations. In this work, the commissioning of photon beams (6 MV and 15 MV) of an Elekta Precise accelerator, using the Monte Carlo code EGSnrc, was performed. The influence of the primary electron beam characteristics on the absorbed dose distribution for two photon qualities was studied. Using different combinations of mean energy and radial FWHM of the primary electron beam, deposited doses were calculated in a water phantom, for different field sizes. Based on the deposited dose in the phantom, depth dose curves and lateral dose profiles were constructed and compared with experimental values measured in an arrangement similar to the simulation. Taking into account the main differences between calculations and measurements, an acceptability criteria based on confidence limits was implemented. As expected, the lateral dose profiles for small field sizes were strongly infl uenced by the radial distribution (FWHM). The combinations of energy/FWHM that best reproduced the experimental results were used to generate the phase spaces, in order to obtain a model with the motorized wedge included and to calculate output factors. A good agreement was obtained between simulations and measurements for a wide range of fi eld sizes , being all the results found within the range of tolerance.
La simulación del cabezal de un acelerador lineal requiere de la determinación de los parámetros que caracterizan el haz primario de electrones que incide en el blanco de radiación, los cuales juegan un papel importante en la exactitud de los cálculos con Monte Carlo. En este trabajo se realizó la habilitación de los haces de fotones (6 MV y 15 MV) de un acelerador Elekta Precise, empleando el código de Monte Carlo EGSnrc. De forma adicional se estudió la influencia que ejerce cambios en las características del haz primario de electrones sobre la distribución de dosis absorbida en diferentes campos de radiación. Basado en la dosis absorbida, curvas de dosis en profundidad y perfiles de dosis se calcularon y compararon con valores experimentales medidos en un arreglo similar a las simulaciones empleando criterios de aceptabilidad. Los perfiles de dosis para campos pequeños resultaron ser fuertemente dependientes de la distribución radial (FWHM). Las combinaciones de energías/FWHM que mejor se ajustaron a las mediciones se emplearon en la generación de espacios de fases, para obtener un modelo con la cuña motorizada y para el cálculo de los factores de campo. Se obtuvo muy buena correspondencia entre las mediciones y las simulaciones realizadas, encontrándose todos los resultados dentro de los márgenes de tolerancias.
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The analysis of some parameters of interest in radiotherapy Medical Physics based on an experimentally validated Monte Carlo model of an Elekta Precise lineal accelerator was performed for 6 and 15 MV photon beams. The simulations were performed using the EGSnrc code. As reference for simulations, the values of the previously obtained optimal beam parameters (energy and FWHM) were used. Deposited dose calculations in water phantoms were done, on typical complex geometries commonly are used in acceptance and quality control tests, such as irregular and asymmetric fields. Parameters such as MLC scatter, maximum opening or closing position, and the separation between them were analyzed from calculations in water. Similarly simulations were performed on phantoms obtained from CT studies of real patients, making comparisons of the dose distribution calculated with EGSnrc and the dose distribution obtained from the computerized treatment planning systems used in routine clinical plans. All the results showed a great agreement with measurements, fi nding all of them within tolerance limits. These results allowed the possibility of using the developed model as a robust verifi cation tool for validating calculations in very complex situations, where the accuracy of the available TPS could be questionable.
El análisis de algunos parámetros de interés en la física médica de la radioterapia, basado en un modelo de Monte Carlo de un acelerador Elekta Precise, fue realizado en este trabajo para los haces de fotones de 6 y 15 MV. Las simulaciones se realizaron con el código EGSnrc. Como referencia para las simulaciones, se emplearon los parámetros óptimos (energía y FWHM) previamente calculados. Los cálculos de la dosis absorbida se realizaron con maniquíes de agua sobre geometrías complejas, comúnmente empleadas en las pruebas de aceptación y control de calidad en la clínica. Parámetros de interés como la dispersión en las MLC, máxima posición de apertura o cierre y la separación entre estas se analizaron a partir de los cálculos en agua. De forma similar se realizaron cálculos en maniquíes construidos a partir de los estudios tomográficos, y comparaciones con los resultados reportados por el sistema de planifi cación en dichos casos. Los resultados obtenidos evidenciaron una gran concordancia con las mediciones, encontrándose dentro de los límites de tolerancias reportados. Estos resultados crean la base para el empleo del modelo de Monte Carlo como una herramienta robusta para la verificación y validación de los cálculos de dosis en situaciones de gran complejidad, donde la exactitud de los sistemas de planificación es cuestionable.
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PURPOSE: The purpose of this study was to investigate influence of different scanning speeds on measurements of photon beam flatness and symmetry. METHODS: Commissioning and quality assurance of linear accelerators require extensive beam measurements. To increase efficacy, we evaluated flatness, symmetry and penumbra of 6MV photon beam using the Varian-TrueBeamTM system. Scanning speeds were 0.3, 0.5, 0.75, 1, 1.5, and 2.5cm/s. Measurements were performed in water phantom (BluePhantom2 , IBA-Dosimetry) at depths of maximum dose, 5,10, and 20cm, for 10×10 cm field size. For each scanning speed and depth, measurements were repeated five times to give results sufficient statistical significance, in both crossline and inline directions. Beam flatness was calculated using variation over mean (80%), whereas symmetry was calculated using point difference quotient (IEC) algorithm. After filed scanning chamber (Wellhofer) was fully stopped, system was paused for stabilization time of 15s to avoid buildup of ripples. RESULTS: It was noticed for all measurements that minimum and maximum flatness and symmetry were recorded when scanning speeds were 0.3cm and 2.5cm, respectively. For depth of maximum dose, maximum flatness and symmetry were 0.82% and 100.58% (crossplane), and 0.94% and 100.96% (inplane). The average was 0.76% and 100.38% (SD 0.04 and 0.12) for crossplane; 0.89% and 100.87% (SD 0.04 and 0.06) for inplane measurements. As the scanning depth increased, flatness and symmetry increased, but SD for all measurements was within the same range (0.04-0.07 and 0.04-0.12). The maximum absolute difference for flatness and symmetry for maximum and minimum speed were 0.16% and 0.34%.However, for scanning speeds from 0.5-1cm/s, results were almost identical with maximum SD 0.03 for both flatness and symmetry. Use of different scanning speeds did not influence penumbra; SD was 0 for all measurements. CONCLUSIONS: This study reveals small influence of scanning speed within predefined range. Consequently, difference in measurements does not have clinical significance.
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PURPOSE: This study examines the optimal angle for a dual-field Stanford technique for TSET at extended SSD (SSD= 1, 2, 3, 4, 5 m) to predict a readily available optimal angle for any SSD. METHODS: The optimal angle at various SSDs is found using detector array. The diode array consists of 9 diodes placed on a vertical board with a measured vertical scale with the origin placed at isocenter. The lateral distance ranges from -100 to +75 cm. A square 36×36 cm2 field is used to deliver dose in HDTSe- delivery mode with a dose rate 2500 MU/min from a Varian Clinic 2300IX linac. Several pairs of gantry angles for the dual field are used, with the first gantry being 70°-78° and the second being 110° -102°. These Result in a dual field of 90° ± θ (θ = 10° - 20°) to build a suitable flatness profile on the vertical axis for treatment. The best group is chosen to determine the optimal angle for each SSD considered. From these optimal angles, an algorithm is determined for any extended SSD treatment. RESULTS: It is found that the optimal angle for TSET does change as one varies the SSD. These angle groups are specific for each SSD giving definite markers for the algorithm. At an SSD of 5 m it has been shown that an optimal angle of θ = 106° produces the best flatness on the vertical axis. While at SSD of 4 m, 9 = 18° Conclusions: An algorithm can now be applied for any treatment center considering a dual- field Stanford technique for TSET simplifying the physics commissioning process for the center in consideration.
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PURPOSE: Besides flattening-filter-free beams, Varian TureBeam Linac also has conventional flattened photon beams. In our facility, we have TrueBeam, Trilogy and iX machines from Varian; they all have same energy specifications: 6 and 10 MV photon beams, as well as 6, 9, 12, 16 and 20 MeV electron beams. This study is to compare the photon and electron beams dosimeter parameters among the three machines. METHODS: Beam data (including PDDs, inline and crossline profiles at various field sizes and various depths) were collected using Sun Nuclear Dosimetry 3D Scanner with nominal 100 cm SSD setup. These data were post processed using Sun Nuclear Dosimetry software, including normalization, interpolation and smoothing. The ion chambers used for scanning are IBA CC13. RESULTS: Photon beams: The percentage depth doses with field sizes of 4×4, 6×6, 10×10, 15×15, 20×20, 30×30 and 40×40 cm × cm of 6 MV and 10 MV photon beams from the three machines are very close. Compared with Varian Golden Beam Data, the maximal variation of PDDs at depths of 5, 10, 15, 20, and 30 cm is 1.0%, with mean value 0.6% and standard deviation 0.28% for 6 MV; for 10 MV beams, they are 2.0% (at depth of 30 cm), 0.9%, and 0.48% respectively. Also, the three machines have very similar beam profiles; the profiles' shoulder, penumbra and umbra match well for both inline and crossline beam profiles at various field sizes and various depths.Electron beams: As compared the percentage surface doses (0.5 mm from the surface), dmax, R90, R80, R50, and R30 of electron beams with energy of 6, 9, 12, 16, and 20 MeV at 10 cm cone, the electron beams of TrueBeam and iX are almost identical. CONCLUSIONS: The 6 and 10 MV photon beam data of TrueBeam, Trilogy, and iX have a same variation range when comparing with Varian Golden Beam Data.
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PURPOSE: Since the 2001 IOM Report Crossing the Quality Chasm: A New Health System for the 21st Century, the need to provide quality metrics in health care has increased. Quality metrics have yet to be defined for the field of radiation oncology. This study represents one institutes initial efforts defining and measuring quality metrics using our electronic medical record and verify system(EMR) as a primary data collection tool. This effort began by selecting meaningful quality metrics rooted in the IOM definition of quality (safe, timely, efficient, effective, equitable and patient-centered care) that were also measurable targets based on current data input and workflow. METHODS: Elekta MOSAIQ 2.30.04D1 was used to generate reports on the number of Special Physics Consults(SPC) charged as a surrogate for treatment complexity, daily patient time in department(DTP) as a measure of efficiency and timeliness, and time from CT-simulation to first LINAC appointment(STL). The number of IMRT QAs delivered in the department was also analyzed to assess complexity. RESULTS: Although initial MOSAIQ reports were easily generated, the data needed to be assessed and adjusted for outliers. Patients with delays outside of radiation oncology such as chemotherapy or surgery were excluded from STL data. We found an average STL of six days for all CT-simulated patients and an average DTP of 52 minutes total time, with 23 minutes in the LINAC vault. Annually, 7.3% of all patient require additional physics support indicated by SPC. CONCLUSIONS: Utilizing our EMR, an entire year's worth of useful data characterizing our clinical experience was analyzed in less than one day. Having baseline quality metrics is necessary to improve patient care. Future plans include dissecting this data into more specific categories such as IMRT DTP, workflow timing following CT-simulation, beam-on hours, chart review outcomes, and dosimetric quality indicators.
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PURPOSE: If the Linac is unavailable during the IMRT treatment schedule, the patient can be switched to a different Linac or prostpond treatment until the origonal Linac is available. The resulting dosimetric difference is estimated and the compromise in the TCP is estimated for both scenarios. This work investigates the feasibility and rationale of switching patients between different accelerators for IMRT in contrast to prostponing the treatment. METHODS: We performed Monte Carlo simulations of photon beams from different Linac models and vendors. Prostate and head and neck treatment plans for Siemens Primus, Primart, Artiste and Varian-21Ex/IX accelerators are studied in this work. Dose distributions for given plans are recalculated using different beam data with the same nominal energy from different Linacs. We have compared DVHs, the maximum, the minimum and the mean dose to the target and critical structures due to switching accelerators. In the process of switching a treatment plan to a different accelerator, there are issues, such as optimum penumbra compensation, dose distribution at the boundary of target and critical structures and multileaf collimator (MLC) leaf width effects, needed to be considered and verified with measurements. In making the final decision whether to switch machines, the TCP based on a linear-quadratic model with time factor is considered. RESULTS: Two DVHs of two plans from Varian and Siemens models are delivered on different machines. Slight dose coverage differences have been observed. TCP estimation with both delayed and without delayed treatments is calculated. Undesired drop of TCP is observed with treatment gap. CONCLUSIONS: Based on the analyses done in this work, it is therapeutically more beneficial to switch a patient to a different machine than to postpone a treatment until the original machine is available, especially for fast growing tumors such as head and neck cancers.
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PURPOSE: To compare measured and calculated doses using Pencil Beam (PB) and Monte Carlo (MC) algorithm on a CIRS thorax phantom for SBRT lung treatments. METHODS: A 6MV photon beam generated by a Primus linac with an Optifocus MLC (Siemens) was used. Dose calculation was done using iPlan v4.1.2 TPS (BrainLAB) by PB and MC (dose to water and dose to medium) algorithms. The commissioning of both algorithms was done reproducing experimental measurements in water. A CIRS thorax phantom was used to compare doses using a Farmer type ion chamber (PTW) and EDR2 radiographic films (KODAK). The ionization chamber, into a tissue equivalent insert, was placed in two position of lung tissue and was irradiated using three treatments plans. Axial dose distributions were measured for four treatments plans using conformal and IMRT technique. Dose distribution comparisons were done by dose profiles and gamma index (3%/3mm). RESULTS: For the studied beam configurations, ion chamber measurements shows that PB overestimate the dose up to 8.5%, whereas MC has a maximum variation of 1.6%. Dosimetric analysis using dose profiles shows that PB overestimates the dose in the region corresponding to the lung up to 16%. For axial dose distribution comparison the percentage of pixels with gamma index bigger than one for MC and PB was, plan 1: 95.6% versus 87.4%, plan 2: 91.2% versus 77.6%, plan 3: 99.7% versus 93.1% and for plan 4: 98.8% versus 91.7%. It was confirmed that the lower dosimetric errors calculated applying MC algorithm appears when the spatial resolution and variance decrease at the expense of increased computation time. CONCLUSIONS: The agreement between measured and calculated doses, in a phantom with lung heterogeneities, is better with MC algorithm. PB algorithm overestimates the doses in lung tissue, which could have a clinical impact in SBRT lung treatments.
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PURPOSE: To develop and validate an EPID-based 4D patient dose reconstruction framework accounting for linac delivery uncertainties, interfractional and intrafractional motions, and interplay effect. METHODS: Patients with fiducial markers were scanned with 4D-CT for SBRT planning. Before treatment, in-room 4D-CT was performed. Both the MLC and the tumor movements were tracked by continuously acquiring EPID images during treatment. Instead of directly using the heterogeneous transit photon fluence measured by the EPID, this method reconstructed the incident beam fluence based on the MLC apertures measured by the EPID and the delivered MU recorded by the linac. To account for the time-dependent-geometry, the incident fluence distributions were sorted into their corresponding phases based on the tumor motion pattern detected by the EPID and accumulated as the incident fluence map for each phase. Together with 4D-CT, it was then used for Monte Carlo dose calculation. Deformable registration was performed to sum up the phase doses for treatment assessment. The feasibility of using the transit EPID images for incident fluence reconstruction was evaluated against EPID in-air measurements. The accuracy of 3D- and 4D-dose reconstruction was validated by a motordriven cylindrical diode array for six clinical SBRT plans. RESULTS: The average difference between the measured and reconstructed fluence maps is within 0.16%. The reconstructed 3D-dose shows 1.4% agreement in the CAX-dose and >98.5% gamma-passing-rate (2%/2mm) in the peripheral-dose. A distorted dose distribution is observed in the measurement for the moving ArcCheck-phantom. The comparison between the measured and the reconstructed 4D-dose without considering interplay fails the gammaevaluation (59%-88.9% gamma-passing-rate). In contrast, when the interplay is considered, the dose distortion phenomena is successfully represented in the reconstructed dose (>97.6% gamma-passing-rate). CONCLUSIONS: The experimental validation demonstrates that the proposed method provides a practical way to reconstruct the fractional 4D-doses received by the patient and enables adaptive SBRT strategy.
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PURPOSE: To examine and facilitate the feasibility of the ArcCheck cylindrical diode array system as a patient specific QA device for CyberKnife radiosurgery delivery. METHODS: There is an obvious necessity for CyberKnife robotic radiosurgery patient QA procedures for hypofractionated treatment of larger planned treatment volumes (PTV), e.g. prostate. This need will increase when the future CyberKnife MLC is introduced. The small unflattened CyberKnife fields, along with the variation of beam-to-detector spatial angles, pose a significant detection challenge for dosimetric systems. The feasibility of the ArcCheck (Sun Nuclear Inc.) cylindrical diode array system for patient-specific QA on the CyberKnife is demonstrated using a beam-to-diode specific angular correction that was developed and has been applied. For localization and tracking, four gold seed fiducial markers were embedded in the system's central plug. We used a Monte Carlo 1% uncertainty for the dose calculation. RESULTS: By disabling the Linac based corrections and applying the custom CyberKnife correction that we developed, the passing rate increased from 39.6% to 99.8% using a 3%3mm gamma criteria for a given lung case. An additional lung case passed 98.5%. In both cases, a 10% dose threshold was used. In addition, brain, trigeminal nerve and lung cases with synchrony tracking are being investigated. CONCLUSIONS: We demonstrated the ArcCheck feasibility for CyberKnife patient specific QA performance. The custom CK angular correction that we developed and applied showed a high passing rate for the lung cases. A verification of the polar angle response should be conducted, in addition to the azimuthal angle that was verified for Linacs. Any data that is being retrieved is additional data to the current chamber point measurement procedures.