ABSTRACT
The accuracy of an out-of-field dose from an Elekta Synergy accelerator calculated using the X-ray Voxel Monte Carlo (XVMC) dose algorithm in the Monaco treatment planning system (TPS) for both low-energy (6 MV) and high-energy (15 MV) photons at cardiac implantable electronic device (CIED) depths was investigated through a comparison between MCNPX simulated out-of-field doses and measured out-of-field doses using three high spatial and sensitive active detectors. In addition, total neutron equivalent dose and fluence at CIED depths of a 15-MV dose from an Elekta Synergy accelerator were calculated, and the corresponding CIED relative neutron damage was quantified. The results showed that for 6-MV photons, the XVMC dose algorithm in Monaco underestimated out-of-field doses in all off-axis distances (average errors: -17% at distances X < 10 cm from the field edge and -31% at distances between 10 < X ≤ 16 cm from the field edge), with an increasing magnitude of underestimation for high-energy (15 MV) photons (up to 11%). According to the results, an out-of-field photon dose at a shallower CIED depth of 1 cm was associated with greater statistical uncertainty in the dose estimate compared to a CIED depth of 2 cm and clinical depth of 10 cm. Our results showed that the relative neutron damage at a CIED depth range for 15 MV photon is 36% less than that reported for 18 MV photon in the literature.
Subject(s)
Heart , Neutrons , Photons , Prostheses and Implants , Radiotherapy Dosage , Algorithms , Humans , Monte Carlo MethodABSTRACT
BACKGROUND: We have recently validated a quarter-time protocol in Myocardial Perfusion Imaging named IQ-SPECT, whose basic principle is to implement a multifocal collimator; However, in clinical practice, it may sometimes be difficult to center the heart in the region of highest magnification of the multifocal collimators (the so-called sweet spot). We therefore aimed to evaluate whether a heart mispositioning may affect results in MPI. METHODS: We simulated a rest study with an anthropomorphic phantom with an in vivo distribution of 400 MBq [(99m)Tc]tetrofosmin, with and without a transmural defect (TD). For each set of images, we performed 5 acquisitions, one with a correct centering and with other 4 degrees of mispositioning. Raw data and reconstructed images were evaluated qualitatively and quantitatively, including no corrections, correction for attenuation, for scatter or for both. We assessed polar plot uniformity, LV wall thickness, and TD and cavity contrast. RESULTS: Images obtained either with a correct heart centering or with mild misposition showed no differences, both qualitatively and quantitatively. Those obtained with major mispositioning differed in uniformity and TD contrast depending on correction parameters. CONCLUSION: This is the first study investigating how a heart mispositioning can affect diagnostic accuracy with IQ-SPECT system. Mild-to-moderate mispositioning (≤2.5 cm) is unlikely to significantly affect results.
Subject(s)
Myocardial Perfusion Imaging , Patient Positioning , Tomography, Emission-Computed, Single-Photon , Anthropometry , Heart/diagnostic imaging , Heart Ventricles/pathology , Humans , Image Processing, Computer-Assisted , Motion , Organophosphorus Compounds , Organotechnetium Compounds , Phantoms, Imaging , Radiopharmaceuticals , Reproducibility of Results , SoftwareABSTRACT
Objective: To investigate the clinical feasibility of a Deep Inspiration Breath Hold (DIBH) 18F-FDG PET-CT acquisition in apnea and compare the results obtained between these acts of acquisition in apnea and in Free Breathing in the evaluation of lung lesions. Material and methods: A pre-clinical phantom study was performed to evaluate the shortest simulated DIBH time according to the minimum detectable lesion that can be detected by our ultrasound scanner. This study was conducted by changing acquisition time and sphere-to-background activity ratio values and by using radioactivity densities similar to those generally found in clinical examinations. In the clinical study, 25 patients with pulmonary lesions underwent a standard whole body 18F-FDG PET-CT scan in free breathing followed by a 20 s single thorax acquisition PET/CT in DIBH acquisition. Results: The phantom study indicated that a 20-s acquisition time provides an accurate evaluation of smallest sphere shaped lesions. In the clinical study, PET-CT scans obtained in DIBH studies showed a significant reduction of misalignment between the PET and CT scan images and an increase of SUVmax compared to free breathing acquisitions. A correlation between the %BH-index and lesion displacement between PET and CT images in FB acquisition was demonstrated, significantly higher for lesions with a displacement > 8 mm. Conclusion: The single 20 s acquisition of DIBH PET-CT is a feasible technique for lung lesion detection in the clinical setting. It only requires a minor increase in examination time without special patient training. 20 s DIBH scan provided a more precise measurement of SUVmax, especially for lesions in the lower lung lobes which usually show greater displacement between PET and CT scan images in FB acquisition (AU)
Objetivo: Estudiar la viabilidad clínica de la adquisición 18F-FDG PET-TC en apnea y comparar los resultados obtenidos entre las adquisiciones en apnea y en respiración libre en la valoración de lesiones pulmonares. Material y métodos: Se ha realizado un estudio preclínico en maniquí con objeto de establecer el tiempo mínimo de adquisición en apnea en función de la más pequeña lesión evidenciable con nuestro tomógrafo. Este estudio se obtuvo modificando los tiempos de adquisición y la relación de actividad entre esfera y fondo utilizando actividades parecidas a las encontradas en la práctica clínica. En el estudio clínico, 25 pacientes con lesiones pulmonares fueron evaluados mediante PET-TC con 18F-FDG en respiración libre y posteriormente en apnea de 20 segundos. Resultados: El estudio en maniquí indicó que una adquisición de 20 segundos es adecuada para la valoración de las esferas más pequeñas. En el estudio clínico, las adquisiciones PET-TC obtenidas en apnea mostraron una significativa reducción de la desalineación entre la imagen PET y la imagen TC y un incremento en el valor del SUVmax respecto a las adquisiciones en respiración libre. Hemos demostrado la existencia de correlación entre el %BH-index y la desalineación en respiración libre, significativamente mayor en las lesiones con desalineación superior a 8 mm. Conclusiones: La adquisición PET-TC de 20 segundos en apnea es una técnica viable para la detección de la lesión pulmonar en el entorno clínico y requiere solo un pequeño aumento en el tiempo de examen sin requerir especial entrenamiento del paciente. La adquisición en apnea aporta una medida más precisa del SUVmax, especialmente en las lesiones de los lóbulos inferiores que normalmente presentan una marcada desalineación entre las imágenes PET y TC (AU)
Subject(s)
Humans , Lung Neoplasms , Positron-Emission Tomography/methods , Inhalation/physiology , Fluorodeoxyglucose F18 , ApneaABSTRACT
PURPOSE: The aim of this study is to report results of measurements of dose to the skin in vivo with radiochromic EBT films in treatments with helical tomotherapy. METHODS AND MATERIALS: In vivo measurements were performed by applying pieces of radiochromic films to the skin or to the inner side of thermoplastic mask before the treatment. The sites of treatment included scalp, brain, head and neck, cranio-spinal axis and lower limbs. Skin dosimetry was performed in a patient who experienced grade 3-4 acute side effects to the skin shortly after the first treatment sessions. For each patient we measured the setup errors using the daily MVCT acquired for image guidance of the treatment. EBT films were read with a flatbed Epson Expression scanner and images were processed with an in-house written routine. RESULTS: A total of 96 measurements of dose to the skin performed on 14 patients. The mean difference and standard error of the mean difference between measured and TPS-calculated dose was -9.2% ± 2.6% for all treatments, -6.6% ± 2.6% for head and neck treatments. These differences were statistically significant at the 0.05 significance level (t-Student test). Planned dose and dose range in the region of measurements were not correlated with dose discrepancy. CONCLUSIONS: Radiochromic EBT films are suitable detectors for surface dose measurements in tomotherapy treatments. Results show that TPS overestimates dose to the skin measured with EBT radiochromic films. In vivo skin measurements with EBT films are a useful tool for quality assurance of tomotherapy treatments, as the treatment planning system may not give accurate dose values at the surface.
