Gilli, Rocío L. (2023) Diseño de un fantoma para auditorías dosimétricas remotas en braquiterapia de alta tasa de dosis / Design of a phantom for remote dosimetric audits in high dose rate brachyterapy. Maestría en Física Médica, Universidad Nacional de Cuyo, Instituto Balseiro.
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Resumen en español
Una de las herramientas esenciales de un programa de QA en radioterapia, que contribuye a garantizar exactitud en la dosimetría de sus tratamientos, es el uso de auditorias dosimétricas. El objetivo de este trabajo fue evaluar la factibilidad de implementar un programa de auditoría dosimétrica postal de nivel II en braquiterapia de alta tasa de dosis (BT HDR) con fuente de 192"Ir por primera vez en Argentina, basando la dosimetría en el uso de luminiscencia ópticamente estimulada (OSL). Para esto, se diseñó y construyó un fantoma solido en PMMA de 80x140x80 mm"3 con dos canales para introducir la fuente y una ranura para colocar un dosímetro OSL nanoDot. El diseño mostró ser resistente a envíos por correo postal, práctico, portátil y económico. Para medir la dosis, se caracterizó y calibró un lote de dosímetros con el equipo Gammamed Plus iX, el cual aloja una fuente de 192"Ir. Se determinaron factores de influencia en el cálculo de dosis propios de los OSLDs, y se analizaron posibles situaciones fuera del protocolo propuesto. Posteriormente, se implementó un estudio piloto de auditoría dosimétrica en colaboración con 3 centros de RT de Argentina, para lo cual se desarrolló un protocolo con instrucciones de planificación e irradiación, una hoja de trabajo y una encuesta para evaluar la calidad del programa propuesto, que se enviaron junto con el fantoma y los dosímetros. Como instancia final, se confeccionó un informe con los resultados obtenidos, el cual fue presentado al físico médico responsable de realizar la medición. Los resultados de la caracterización de los OSLD fueron muy satisfactorios, estando todos los factores de influencia dentro de límites publicados internacionalmente. La incertidumbre para el cálculo de dosis con el sistema dosimétrico propuesto fue del ±4% con un nivel de confianza del 95 %. A partir de este valor se estableció como nivel de aceptación ´optimo aquellas desviaciones porcentuales entre la dosis reportada por el TPS del centro y la dosis medida con OSLD, menores al ±4 %; y aceptables, aquellas desviaciones entre el ±4% y ±5 %. En este contexto, los resultados obtenidos en los 3 centros se encontraron dentro del limite ´optimo, independientemente del equipo HDR auditado. Asimismo, a través de la encuesta, los centros indicaron sensaciones positivas hacia el proyecto, destacando la facilidad de uso del fantoma y la claridad de la instrucciones tanto para planificación como para irradiación. Como conclusión, en esta primera experiencia se obtuvieron resultados muy alentadores, tanto en el uso de los OSLDs como dosímetros para 192"Ir, como del estudio piloto en sí, que serviría de base para un futuro programa oficial de auditorías dosimétricas en BT HDR por primera vez en nuestro país.
Resumen en inglés
One of the essential tools in a QA program in radiotherapy, contributing to ensuring accuracy in the dosimetry of treatments, is the use of dosimetric audits. The objective of this work was to evaluate the feasibility of implementing a level II postal dosimetric audit program in high-dose-rate brachytherapy (HDR BT) with a 192"Ir source for the first time in Argentina, basing dosimetry on the use of optically stimulated luminescence (OSL). For this purpose, a solid PMMA phantom of dimensions 80x140x80 mm"3 was designed and constructed with two channels to insert the source and a slot to place an OSL nanoDot dosimeter. The design proved to be resistant to postal shipments, practical, portable, and cost-effective. To measure the dose, a batch of dosimeters was characterized and calibrated with the Gammamed Plus iX equipment, which houses a 192"Ir source. Influence factors in the dose calculation specific to OSLDs were determined, and potential deviations from the proposed protocol were analyzed. Subsequently, a pilot dosimetric audit study was implemented in collaboration with three radiotherapy centers in Argentina. For this, a protocol with planning and irradiation instructions, a worksheet, and a survey to assess the quality of the proposed program were developed and sent along with the phantom and dosimeters. As a final step, a report with the obtained results was prepared and presented to the medical physicist responsible for carrying out the measurement. The results of the OSLD characterization were very satisfactory, with all influencing factors falling within internationally published limits. The uncertainty for dose calculation with the proposed dosimetric system was ±4% with a 95% confidence level. Based on this value, deviations between the dose reported by the center’s TPS and the dose measured with OSLDs were established as optimal if they were less than ±4%, and acceptable if they fell between ±4% and ±5%. In this context, the results obtained in all three centers were within the optimal limit, regardless of the audited HDR equipment. Additionally, through the survey, the centers expressed positive feedback about the project, highlighting the ease of use of the phantom and the clarity of instructions for both planning and irradiation. In conclusion, in this first experience, very encouraging results were obtained, both in the use of OSLDs as dosimeters for 192"Ir, and in the pilot study itself, which would serve as the basis for a future official program of dosimetric audits in BT HDR for the first time in our country.
| Tipo de objeto: | Tesis (Maestría en Física Médica) |
|---|---|
| Palabras Clave: | Audits; Auditoría; Brachytherapy; Braquiterapia; [Phantom; Fantoma] |
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| Materias: | Medicina > Física médica Medicina > Dosimetría |
| Divisiones: | FUESMEN |
| Código ID: | 1229 |
| Depositado Por: | Marisa G. Velazco Aldao |
| Depositado En: | 18 Mar 2024 12:25 |
| Última Modificación: | 18 Mar 2024 12:25 |
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