RESUMEN
PURPOSE: In this article we report on the results of a survey of physics plan review practices conducted by the Cancer Care Ontario Communities of Practice and the variations in practice between and within centers. METHODS: The medical physicists at each center worked together to complete the survey and submit a single response for that center. A 4-point Likert scale, used to report the variation in practice at each center, was quantified into two parameters: "Intra-center variation", the distribution of responses within the center, and "Variation between centers", the difference between the center's response and the provincial mean. These metrics were correlated with center characteristics to identify factors that impacted on variations in practice. RESULTS: Bolus and heterogeneity correction were the only two items checked by all physicists in all centers. In more than half of the centers, image registration and DVH binning are not likely checked by physics. A significant difference in the variation between centers is observed for centers that used a single vendor's products. Centers that used an official checklist indicated higher levels and a wider range of Intra-center variation. Higher workload did not affect the variation in checking patterns between physicists in the same center. CONCLUSIONS: The effect of a center's resources on their checking practice suggest that local environment and workflow be accounted for when implementing TG275 guidelines. The observation that standardized checklists did not reduce checking variability point to the importance of following the checklist development guidelines in MPPG4 to avoid ineffective checklists.
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Física , Planificación de la Radioterapia Asistida por Computador , Informe de Investigación , Flujo de TrabajoRESUMEN
A first-time survey across 15 cancer centers in Ontario, Canada, on the current practice of patient-specific quality assurance (PSQA) for intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) delivery was conducted. The objectives were to assess the current state of PSQA practice, identify areas for potential improvement, and facilitate the continued improvement in standardization, consistency, efficacy, and efficiency of PSQA regionally. The survey asked 40 questions related to PSQA practice for IMRT/VMAT delivery. The questions addressed PSQA policy and procedure, delivery log evaluation, instrumentation, measurement setup and methodology, data analysis and interpretation, documentation, process, failure modes, and feedback. The focus of this survey was on PSQA activities related to routine IMRT/VMAT treatments on conventional linacs, including stereotactic body radiation therapy but excluding stereotactic radiosurgery. The participating centers were instructed to submit answers that reflected the collective view or opinion of their department and represented the most typical process practiced. The results of the survey provided a snapshot of the current state of PSQA practice in Ontario and demonstrated considerable variations in the practice. A large majority (80%) of centers performed PSQA measurements on all VMAT plans. Most employed pseudo-3D array detectors with a true composite (TC) geometry. No standard approach was found for stopping or reducing frequency of measurements. The sole use of delivery log evaluation was not widely implemented, though most centers expressed interest in adopting this technology. All used the Gamma evaluation method for analyzing PSQA measurements; however, no universal approach was reported on how Gamma evaluation and pass determination criteria were determined. All or some PSQA results were reviewed regularly in two-thirds of the centers. Planning related issues were considered the most frequent source for PSQA failures (40%), whereas the most frequent course of action for a failed PSQA was to review the result and decide whether to proceed to treatment.
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Radiocirugia , Radioterapia de Intensidad Modulada , Canadá , Humanos , Dosificación Radioterapéutica , Planificación de la Radioterapia Asistida por ComputadorRESUMEN
Volumetric-modulated arc therapy (VMAT) treatment plans that are highly modulated or complex may result in disagreements between the planned dose distribution and the measured dose distribution. This study investigated established VMAT complexity metrics as a means of predicting phantom-based measurement results for 93 treatments delivered on a TrueBeam linac, and 91 treatments delivered on two TrueBeam STx linacs. Complexity metrics investigated showed weak correlations to gamma passing rate, with the exception of the Modulation Complexity Score for VMAT, yielding moderate correlations. The Spearman's rho values for this metric were 0.502 (P < 0.001) and 0.528 (P < 0.001) for the TrueBeam and TrueBeam STx, respectively. Receiver operating characteristic analysis was also performed. The aperture irregularity on the TrueBeam achieved a 53% true positive rate and a 9% false-positive rate to correctly identify complex plans. Similarly, the average field width on the TrueBeam STx achieved a 60% true-positive rate and an 8% false-positive rate. If incorporated into clinical workflow, these thresholds can identify highly modulated plans and reduce the number of dose verification measurements required.
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Radioterapia de Intensidad Modulada , Humanos , Aceleradores de Partículas , Fantasmas de Imagen , Dosificación Radioterapéutica , Planificación de la Radioterapia Asistida por ComputadorRESUMEN
The American Association of Physicists in Medicine recommends that the reference dose-rate distribution, used for treatment planning for low-energy photon brachytherapy sources in routine clinical use, must be based on at least two independent determinations: one using experimentally measured dose rates and one using Monte Carlo simulation dosimetry techniques. In this work, we present an approach for developing consensus dosimetry parameters from various independent reference dosimetry studies for interstitial brachytherapy sources. This approach is applied to four recently published papers on the dosimetric properties of the BrachySeed Model LS-1 125I seed. Consensus values for the dose-rate constant, radial dose function, and anisotropy parameters are presented for the LS-1 Model 125I seed.
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Braquiterapia/métodos , Braquiterapia/normas , Consenso , Radioisótopos de Yodo/análisis , Radioisótopos de Yodo/uso terapéutico , Radiometría/métodos , Radiometría/normas , Algoritmos , Humanos , Radiofármacos/análisis , Radiofármacos/uso terapéutico , Dosificación Radioterapéutica , Planificación de la Radioterapia Asistida por Computador/métodos , Planificación de la Radioterapia Asistida por Computador/normas , Estándares de Referencia , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Estados UnidosRESUMEN
Recently, 103Pd brachytherapy sources have been increasingly used for interstitial implants as an alternative to 125I sources. The BrachySeedPd-103 Model Pd-1 seed is one of the latest in a series of new brachytherapy sources that have become available commercially. The dosimetric properties of the seed were investigated by Monte Carlo simulation, which was performed using the Integrated Tiger Series CYLTRAN code. Following the AAPM Task Group 43 formalism, the dose rate constant, radial dose function, and anisotropy parameters were determined. The dose rate constant, A, was calculated to be 0.613 +/- 3% cGy h(-1) U(-1). This air kerma strength was derived from Monte Carlo simulation using the point extrapolation method. The radial dose function, g(r), was computed at distances from 0.15 to 10 cm. The anisotropy function, F(r,theta), and anisotropy factor, phi(an)(r), were calculated at distances from 0.5 to 7 cm. The anisotropy constant, phi(an), was determined to be 0.978, which is closer to unity than most other 103Pd seeds, indicating a high degree of uniformity in dose distribution. The dose rate constant and the radial dose function were also investigated by analytical modeling, which served as an independent evaluation of the Monte Carlo data, and found to be in good agreement with the Monte Carlo results.
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Braquiterapia/instrumentación , Braquiterapia/métodos , Modelos Biológicos , Paladio/administración & dosificación , Radiometría/métodos , Planificación de la Radioterapia Asistida por Computador/métodos , Anisotropía , Braquiterapia/normas , Simulación por Computador , Humanos , Modelos Estadísticos , Método de Montecarlo , Radioisótopos/uso terapéutico , Dosificación Radioterapéutica , Planificación de la Radioterapia Asistida por Computador/normas , Dispersión de Radiación , Sensibilidad y Especificidad , Programas InformáticosRESUMEN
The BrachySeed model LS-1 is one of the latest in a series of new brachytherapy 125I seeds that have recently become available commercially for interstitial implants. The dosimetric properties of the seed were investigated analytically, experimentally, and by Monte Carlo simulation. Following the AAPM Task Group 43 formalism, the radial dose function, dose rate constant, and anisotropy parameters were determined. Experimental measurements were made in solid water-equivalent phantoms using GafChromic MD-55-2 films, with correction for the low energy film response. Analyses were carried out from absolute measurements, as well as relative measurements against the Nycomed Amersham OncoSeed Model 6711, which also served to validate our experimental methodology. A small, but systematic difference in the absolute measurements was observed depending on the duration of the irradiation. Monte Carlo simulation was performed using the Integrated Tiger Series CYLTRAN code. We benchmarked the code by comparing the dose parameters of Model 6702 with published values. The radial dose function, g(r), of the Model LS-1 seed was computed at distances from 0.25 to 10 cm by analytical and Monte Carlo calculations with reasonably good agreement. The suggested dose rate constant, A, based on the Monte Carlo simulation is 0.90+/-0.03 cGy h(-1) U(-1). This value is smaller than, but overlaps the experimental determination of 0.98+/-0.06 cGy h(-1) U(-1). The anisotropy function, F(r, theta), and anisotropy factor, phi(an)(r), compared favorably with those of the Model 6711.