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Advisor(s)
Abstract(s)
Objectivo: O objectivo do estudo foi testar a fiabilidade da detecção de erros, introduzidos aleatoriamente nas folhas do MLC, pelos sistemas utilizados no controlo de qualidade de arco terapia.
Material e Métodos: Foram introduzidos erros intencionais nas posições das folhas do MLC em doze planeamentos dosimétricos de arco terapia de quatro locais anatómicos: pulmão, pélvico, cerebral e cabeça e pescoço. Os erros introduzidos eram de sete amplitudes diferentes: 0,25, 0,5, 1, 2, 2,5, 3 e 5mm. Os planos modificados foram comparados aos planos originais através do sistema de dosimetria portal, sendo as medidas analisadas através do método de análise gamma com o critério de 3%/3mm.
Resultados: Não existiu relação entre a amplitude dos erros e a percentagem de detecção pelo software de Dosimetria Portal. Comparando planos dosimétricos do mesmo local anatómico, não se observaram diferenças significativas de detecção de erros. Avaliando as percentagens de detecção dos diferentes locais anatómicos verificou-se percentagens de detecção mais elevadas para os casos de pulmão e cabeça e pescoço, 83,3% e 45,8%. Tendo o pélvico e o cerebral percentagens de detecção de 12,5% e 20,8%. Os casos complexos a nível de heterogeneidade das folhas, pulmão e cabeça e pescoço apresentaram percentagens de detecção superiores comparativamente aos casos simples, pélvico e cerebral. O critério de 3%/3mm pode não ser suficientemente sensível para detectar todas as amplitudes dos erros que foram introduzidos neste estudo, principalmente em planos simples. Não houve diferença significativa de percentagens de detecção entre as folhas localizadas na periferia e no centro.
Conclusão: A dosimetria portal em planeamentos dosimétricos simples é menos sensível a erros nas posições das folhas do MLC, e a análise gamma com o critério de 3%/3mm não detecta a maioria das amplitudes utilizadas nestes casos. Em planeamentos complexos, o sistema utilizado tem uma performance aceitável em termos de detecção de erro a todas as amplitudes estudadas. É importante que cada serviço de radioterapia estabeleça protocolos adequados, de acordo com as técnicas praticadas e dispositivos disponíveis, de forma a garantir um sistema de controlo de qualidade eficiente.
Purpose: The purpose of the present study was to test the reliability in the detection of specific errors introduced randomly in the MLC by the systems used for arc therapy quality assurance. Material and Methods: Intentional errors were introduced in the MLC positions in twelve arc therapy dosimetric plans of four anatomic sites: lung, pelvic, brain and head and neck. The introduced errors were from seven different amplitudes: 0.25, 0.5, 1, 2, 2.5, 3 and 5mm. The modified plans were compared to original plans by Portal Dosimetry software. The measures were analyzed by gamma analysis with 3%/3mm criteria. Results: There was no relationship between the errors amplitude and percentage of errors detected by the portal dosimetry. Comparing dosimetric plans of the same anatomical site, no significant differences in error detection were observed. Evaluating the percentage detection in different anatomical sites it was found higher proportions of detection for cases of lung and head and neck, 83.3% and 45.8%. The brain and pelvic cases had detection percentages of 12.5% and 20.8%. Complex plans as lung and H&N cases, show superior detection percentages than pelvic and brain. The 3%/3mm criteria may not be sufficiently sensitive to detect all the amplitudes of the errors that were introduced in this study particularly in simple plans. There was no significant difference in detection percentage between the leaves located in periphery and center. Conclusion: The portal dosimetry software in simple plans is less sensitive to errors in the positions of the MLC leaves, and the gamma analysis with 3%/3mm criteria does not detect most of the amplitudes used in these cases. In complex plans, the system used has an acceptable performance in terms of error detection for all the studied amplitudes. It’s important that each radiotherapy service establish appropriate protocols in accordance with the available devices and techniques practiced so as to ensure an efficient quality assurance system.
Purpose: The purpose of the present study was to test the reliability in the detection of specific errors introduced randomly in the MLC by the systems used for arc therapy quality assurance. Material and Methods: Intentional errors were introduced in the MLC positions in twelve arc therapy dosimetric plans of four anatomic sites: lung, pelvic, brain and head and neck. The introduced errors were from seven different amplitudes: 0.25, 0.5, 1, 2, 2.5, 3 and 5mm. The modified plans were compared to original plans by Portal Dosimetry software. The measures were analyzed by gamma analysis with 3%/3mm criteria. Results: There was no relationship between the errors amplitude and percentage of errors detected by the portal dosimetry. Comparing dosimetric plans of the same anatomical site, no significant differences in error detection were observed. Evaluating the percentage detection in different anatomical sites it was found higher proportions of detection for cases of lung and head and neck, 83.3% and 45.8%. The brain and pelvic cases had detection percentages of 12.5% and 20.8%. Complex plans as lung and H&N cases, show superior detection percentages than pelvic and brain. The 3%/3mm criteria may not be sufficiently sensitive to detect all the amplitudes of the errors that were introduced in this study particularly in simple plans. There was no significant difference in detection percentage between the leaves located in periphery and center. Conclusion: The portal dosimetry software in simple plans is less sensitive to errors in the positions of the MLC leaves, and the gamma analysis with 3%/3mm criteria does not detect most of the amplitudes used in these cases. In complex plans, the system used has an acceptable performance in terms of error detection for all the studied amplitudes. It’s important that each radiotherapy service establish appropriate protocols in accordance with the available devices and techniques practiced so as to ensure an efficient quality assurance system.