BackgroundThe aim of this study was to retrospectively evaluate the patient effective dose (ED) for different PET/CT procedures performed with a variety of PET radiopharmaceutical compounds.PET/CT studies of 210 patients were reviewed including Torso (n = 123), Whole body (WB) (n = 36), Head and Neck Tumor (HNT) (n = 10), and Brain (n = 41) protocols with 18FDG (n = 170), 11C-CHOL (n = 10), 18FDOPA (n = 10), 11C-MET (n = 10), and 18F-florbetapir (n = 10). ED was calculated using conversion factors applied to the radiotracer activity and to the CT dose-length product.ResultsTotal ED (mean ± SD) for Torso-11C-CHOL, Torso-18FDG, WB-18FDG, and HNT-18FDG protocols were 13.5 ± 2.2, 16.5 ± 4.5, 20.0 ± 5.6, and 15.4 ± 2.8 mSv, respectively, where CT represented 77, 62, 69, and 63% of the protocol ED, respectively. For 18FDG, 18FDOPA, 11C-MET, and 18F-florbetapir brain PET/CT studies, ED values (mean ± SD) were 6.4 ± 0.6, 4.6 ± 0.4, 5.2 ± 0.5, and 9.1 ± 0.4 mSv, respectively, and the corresponding CT contributions were 11, 14, 23, and 26%, respectively. In 18FDG PET/CT, variations in scan length and arm position produced significant differences in CT ED (p < 0.01). For dual-time-point imaging, the CT ED (mean ± SD) for the delayed scan was 3.8 ± 1.5 mSv.ConclusionsThe mean ED for body and brain PET/CT protocols with different radiopharmaceuticals ranged between 4.6 and 20.0 mSv. The major contributor to total ED for body protocols is CT, whereas for brain studies, it is the PET radiopharmaceutical.
This study aimed to describe the commissioning of small field size radiosurgery cones in a 6-MV flattening filter free (FFF) beam and report our measured values. Four radiosurgery cones of diameters 5, 10, 12.5, and 15 mm supplied by Elekta Medical were commissioned in a 6-MV FFF beam from an Elekta Versa linear accelerator. The extraction of a reference signal for measuring small fields in scanning mode is challenging. A transmission chamber was attached to the lower part of the collimators and used for percentage depth dose (PDD) and profile measurements in scanning mode with a stereotactic diode. Tissue-maximum ratios (TMR) and output factors (OF) for all collimators were measured with a stereotactic diode (IBA). TMR and the OF for the largest collimator were also acquired on a polystyrene phantom with a microionization chamber of 0.016 cm volume (PTW Freiburg PinPoint 3D). Measured TMR with diode and PinPoint microionization chamber agreed very well with differences smaller than 1% for depths below 20 cm, except for the smaller collimator, for which differences were always smaller than 2%. Calculated TMR were significantly different (up to 7%) from measured TMR. OF measured with diode and chamber showed a difference of 3.5%. The use of a transmission chamber allowed the measurement of the small-field dosimetric properties with a simple setup. The commissioning of radiosurgery cones in FFF beams has been performed with essentially the same procedures and recommended detectors used with flattened beams. Good agreement was found between TMR measurements acquired with the IBA stereotactic diode and the PinPoint 3D microionization chamber. The transmission chamber overcomes the problem of extracting a reference signal and is of great help for small-field commissioning.
Purpose To determine which imaging method used during radioembolization (RE) work-up: contrast-enhanced computed tomography (CECT), 99mTc-MAA-SPECT/CT or cone beam-CT (CBCT), more accurately predicts the final target volume (TgV) as well as the influence that each modality has in the dosimetric calculation. Methods TgVs from 99mTc-MAA-SPECT/CT, CECT and CBCT were consecutively obtained in 24 patients treated with RE and compared with 90Y PET/CT TgV. Using the TgVs estimated by each imaging modality and a fictitious activity of 1 GBq, the corresponding absorbed doses by tumor and non-tumoral parenchyma were calculated for each patient. The absorbed doses for each modality were compared with the ones obtained using 90Y PET/CT TgV. Results 99mTc-MAA-SPECT/CT predicted 90Y PET/CT TgV better than CBCT or CECT, even for selective or superselective administrations. Likewise, 99mTc-MAA-SPECT/CT showed dosimetric values more similar to those obtained with 90Y PET/CT. Nevertheless, CBCT provided essential information for RE planning, such as ensuring the total coverage of the tumor and, in cases with more than one feeding artery, splitting the activity according to the volume of tumor perfused by each artery. Conclusion The joint use of 99mTc-MAA-SPECT/CT and CBCT optimizes dosimetric planning for RE procedures, enabling a more accurate personalized approach.
La radioembolización (RE) consiste en la administración por vía intraarterial hepática de microesferas marcadas con un isótopo radiactivo que emita radiación de corto alcance, que permita impartir dosis absorbidas elevadas en el tejido tumoral y limitar la dosis absorbida en el tejido sano. Su eficacia se basa en la vascularización característica del hígado y de los tumores hepáticos. El tejido hepático sano recibe su flujo sanguíneo a través de la vena porta, mientras que los tumores hepáticos se irrigan principalmente por la arteria hepática. El pequeño tamaño de las microesferas permite que lleguen hasta el tumor a través de la vasculatura hepática, quedando permanentemente implantadas dentro del sistema vascular tumoral e impidiendo su paso a la circulación venosa. La planificación de los tratamientos de RE, a partir de la imagen 99mTc-MAA SPECT-CT, es la única herramienta disponible que permite realizar una evaluación dosimétrica personalizada previa a la administración del tratamiento. El cálculo preciso de las dosis absorbidas favorece la optimización tanto de la selección de pacientes candidatos a RE como del proceso de planificación para maximizar su eficacia terapéutica y minimizar la toxicidad en tejido sano. Por tanto, una metodología dosimétrica optimizada y reproducible es no sólo importante, sino esencial. En la actualidad, prácticamente ninguno de los procesos que se engloban dentro de un procedimiento dosimétrico está completamente estandarizado. En este contexto, surge un gran interés en abordar la comparación de diferentes técnicas en una única serie de pacientes, que facilite la estandarización del uso de las mismas. El objetivo de este estudio de investigación es optimizar y estandarizar el procedimiento dosimétrico en la planificación de los tratamientos de RE hepática con 90Y-microesferas, cuantificando la repercusión de cada variante metodológica en la dosis absorbida ycaracterizando su impacto clínico. Se consideraron cuatro modelos dosimétricos diferentes, dos métodos multicompartimentales, el método de partición y el modelo de partición multitumor planteado como novedad en este trabajo, y dos métodos de dosimetría a nivel de vóxel. Se compararon las dosis absorbidas, tanto en el tejido sano como en el tejido tumoral, resultantes de aplicar estos modelos dosimétricos sobre las imágenes pre-tratamiento. Del análisis de los resultados obtenidos, se desprende que llevar a cabo una segmentación completa de los compartimentos, a partir de los contornos del hígado, el volumen diana y cada una de las lesiones individuales que constituyen el conglomerado tumoral, contribuye a que los cálculos dosimétricos sean más precisos, lo que permite optimizar la selección de pacientes candidatos a RE y aporta información importante para decidir el mejor esquema terapéutico para el paciente. Además, las metodologías empleadas para determinar parámetros como el índice TN y el factor de calibración han demostrado tener un impacto importante en el cálculo de las dosis absorbidas resultantes. Así, el procedimiento empleado tiene un papel fundamental en la dosimetría de los tratamientos de RE, y es esencial establecer una única metodología para su cálculo. El nuevo modelo de partición multi-tumor es una herramienta fácil de implementar y podría ser de gran utilidad en aquellos centros en los que no es posible implementar métodos de dosimetría a nivel de vóxel, ya que aporta una mayor precisión que el modelo de partición estándar en el cálculo de la dosis absorbida en el tejido tumoral. Como resultado final de este trabajo se diseñó un algoritmo de recomendaciones, cuyo principal objetivo es contribuir a la estandarización de los métodos empleados en la dosimetría pre-tratamiento. Así, en función de las herramientas disponibles y de los datos recogidos de cada paciente, cada centro puede elegir la forma de proceder más adecuada para el cálculo de las dosis absorbidas.
Introduction A rapid deploy of unexpected early impact of the COVID pandemic in Spain was described in 2020. Oncology practice was revised to facilitate decision-making regarding multimodal therapy for prevalent cancer types amenable to multidisciplinary treatment in which the radiotherapy component searched more efficient options in the setting of the COVID-19 pandemic, minimizing the risks to patients whilst aiming to guarantee cancer outcomes. Methods A novel Proton Beam Therapy (PBT), Unit activity was analyzed in the period of March 2020 to March 2021. Institutional urgent, strict and mandatory clinical care standards for early diagnosis and treatment of COVID-19 infection were stablished in the hospital following national health-authorities’ recommendations. The temporary trends of patients care and research projects proposals were registered. Results 3 out of 14 members of the professional staff involved in the PBR intra-hospital process had a positive test for COVID infection. Also, 4 out of 100 patients had positive tests before initiating PBT, and 7 out of 100 developed positive tests along the weekly mandatory special checkup performed during PBT to all patients. An update of clinical performance at the PBT Unit at CUN Madrid in the initial 500 patients treated with PBT in the period from March 2020 to November 2022 registers a distribution of 131 (26%) pediatric patients, 63 (12%) head and neck cancer and central nervous system neoplasms and 123 (24%) re-irradiation indications. In November 2022, the activity reached a plateau in terms of patients under treatment and the impact of COVID pandemic became sporadic and controlled by minor medical actions. At present, the clinical data are consistent with an academic practice prospectively (NCT05151952). Research projects and scientific production was adapted to the pandemic evolution and its influence upon professional time availability. Seven research projects based in public funding were activated in this period and preliminary data on molecular imaging guided proton therapy in brain tumors and post-irradiation patterns of blood biomarkers are reported. Conclusions Hospital-based PBT in European academic institutions was impacted by COVID-19 pandemic, although clinical and research activities were developed and sustained. In the post-pandemic era, the benefits of online learning will shape the future of proton therapy education.
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