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Avaliação das doses nos órgãos em tomografia computorizada de planeamento em radioterapia
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Abstract(s)
A tomografia computorizada (TC) utilizada no planeamento de tratamentos de radioterapia (RT), utiliza aquisições de imagens extensas e protocolos complexos, o que tem vindo a reforçar a importância de se avaliar as doses inerentes à prática, e garantir a segurança radiológica dos doentes. A avaliação da exposição associada a estas aquisições é relevante, de modo a garantir que as doses administradas aos doentes são otimizadas, minimizando o risco de efeitos indesejados.
Este estudo tem como objetivo avaliar os parâmetros e protocolos de aquisição de imagens nos exames de TC de planeamento de RT, para as indicações clínicas de cabeça e pescoço, sistema nervoso central (SNC), pulmão 4D, pulmão Stereotactic Body Radiation Therapy (SBRT), mama, mama e axila, mama Deep Inspiration Breath Hold (DIBH) e próstata. Ainda como objetivo pretende-se estimar as doses absorvidas pelos órgãos, a dose efetiva, analisar níveis de referência de diagnóstico (NRD) locais, e definir valores típicos de dose.
A análise foi realizada para uma amostra de 151 doentes que realizaram TC de planeamento, com o equipamento da marca General Electric, modelo Discovery TM RT. As estimativas dosimétricas foram calculadas com recurso ao software The National Cancer Institute Dosimetry System for Computed Tomography (NCICT). Para cada exame registaram-se os parâmetros de aquisição das imagens, os intervalos de aquisição, os diâmetros anatómicos dos doentes, os valores de Volume Computed Tomography Dose Index (CTDIvol), Dose-Length Product (DLP), o Size-Specific Dose Estimate (SSDE), bem como as doses absorvidas pelos órgãos e a dose efetiva estimada.
Os objetivos propostos foram alcançados, pois analisaram-se os parâmetros de aquisição dos protocolos de TC de planeamento de RT, os comprimentos de aquisição, estimaram-se as doses absorvidas nos órgãos e as doses efetivas. Os resultados foram comparados com a literatura existente, permitindo uma avaliação crítica. Analisaram-se NRD locais e definiu- se os valores típicos de exposição.
Propuseram-se valores típicos de dose, baseados no P50 da distribuição dos valores de CTDIvol e de DLP, para as indicações clínicas de cabeça e pescoço de (12,90 mGy e 567 mGy.cm), SNC (11,60 mGy e 383 mGy.cm), mama (13,10 mGy e 496 mGy.cm), mama e axila (13 mGy e 526 mGy.cm), mama DIBH (10,60 mGy e 809 mGy.cm), pulmão 4D (30,70 mGy e 2423 mGy.cm) e pulmão SBRT (39,90 mGy e 2141 mGy.cm) e para a próstata (15,10 mGy e 717 mGy.cm).
Como perspetiva futura, destaca-se a importância de aumentar a casuística, integrar critérios de avaliação da qualidade de imagem e realizar comparações com outras ferramentas de cálculo de dose. Destaca-se também a possibilidade de realizar estimativas do risco decorrentes da exposição à TC de planeamento.
Os resultados obtidos permitem uma melhor compreensão das práticas locais de aquisição em TC de planeamento de RT, reforçam a importância da avaliação periódica dos protocolos e a relevância da proteção e segurança radiológica na prática clínica. Além disso, constituem um ponto de partida à implementação de estratégias de otimização e à definição de NRD no serviço de RT.
Computed tomography (CT) used in radiotherapy (RT) treatment planning involves extensive image acquisition and complex protocols, which has reinforced the importance of assessing the doses inherent in the practice and ensuring the patients’ radiation safety. The assessment of exposure associated with these acquisitions is essential to ensure that the doses administered to patients are optimised, minimising the risk of undesired effects. This study aims to evaluate the imaging acquisition parameters and protocols used in CT simulation scans for RT planning, focusing on clinical indications including head and neck, central nervous system (CNS), 4D lung, Stereotactic Body Radiation Therapy (SBRT) lung, breast, breast and axilla, Deep Inspiration Breath Hold (DIBH) breast, and prostate. Additionally, the study seeks to estimate doses absorbed by the organs and effective dose, analyse local diagnostic reference levels (DRLs), and define typical dose values. The analysis was conducted on a sample of 151 patients who underwent planning CT scans, acquired using a GE Discovery TM RT CT scanner. Dosimetric estimates were calculated using The National Cancer Institute Dosimetry System for Computed Tomography (NCICT) software. For each examination, the image acquisition parameters, acquisition intervals, anatomical diameters of patients, Volume Computed Tomography Dose Index (CTDIvol), Dose-Length Product (DLP), Size-Specific Dose Estimate (SSDE) values, as well as the absorbed doses by the organs and the estimated effective dose were recorded. The proposed objectives were achieved, as the acquisition parameters of the RT planning CT protocols and acquisition lengths were analysed, and the doses absorbed by the organs and effective doses were estimated. The results were compared with the existing literature, allowing for a critical evaluation. Local DRL were analysed and typical exposure values were defined. Typical dose values were proposed based on the 50th percentile (P50) of the CTDIvol and DLP distributions for the clinical indications of the head and neck (12,90 mGy and 567 mGy·cm), CNS (11,60 mGy and 383 mGy·cm), breast (13,10 mGy and 496 mGy·cm), breast and axilla (13 mGy and 526 mGy·cm), breast DIBH (10,60 mGy and 809 mGy·cm), 4D lung (30,70 mGy and 2423 mGy·cm), lung SBRT (39,90 mGy and 2141 mGy·cm), and prostate (15,10 mGy and 717 mGy·cm). As a future perspective, it is important to expand the sample, integrate image quality assessment criteria, and make comparisons with other dose calculation tools. It is also worth highlighting the potential to estimate the risk associated with exposure from planning CT scans, in the future. The results obtained allow for a better understanding of local acquisition practices in RT planning CT, reinforce the importance of periodic evaluation of protocols, and highlight the relevance of radiation protection and safety in clinical practice. Furthermore, they constitute a starting point for the implementation of optimisation strategies and the definition of DRL.
Computed tomography (CT) used in radiotherapy (RT) treatment planning involves extensive image acquisition and complex protocols, which has reinforced the importance of assessing the doses inherent in the practice and ensuring the patients’ radiation safety. The assessment of exposure associated with these acquisitions is essential to ensure that the doses administered to patients are optimised, minimising the risk of undesired effects. This study aims to evaluate the imaging acquisition parameters and protocols used in CT simulation scans for RT planning, focusing on clinical indications including head and neck, central nervous system (CNS), 4D lung, Stereotactic Body Radiation Therapy (SBRT) lung, breast, breast and axilla, Deep Inspiration Breath Hold (DIBH) breast, and prostate. Additionally, the study seeks to estimate doses absorbed by the organs and effective dose, analyse local diagnostic reference levels (DRLs), and define typical dose values. The analysis was conducted on a sample of 151 patients who underwent planning CT scans, acquired using a GE Discovery TM RT CT scanner. Dosimetric estimates were calculated using The National Cancer Institute Dosimetry System for Computed Tomography (NCICT) software. For each examination, the image acquisition parameters, acquisition intervals, anatomical diameters of patients, Volume Computed Tomography Dose Index (CTDIvol), Dose-Length Product (DLP), Size-Specific Dose Estimate (SSDE) values, as well as the absorbed doses by the organs and the estimated effective dose were recorded. The proposed objectives were achieved, as the acquisition parameters of the RT planning CT protocols and acquisition lengths were analysed, and the doses absorbed by the organs and effective doses were estimated. The results were compared with the existing literature, allowing for a critical evaluation. Local DRL were analysed and typical exposure values were defined. Typical dose values were proposed based on the 50th percentile (P50) of the CTDIvol and DLP distributions for the clinical indications of the head and neck (12,90 mGy and 567 mGy·cm), CNS (11,60 mGy and 383 mGy·cm), breast (13,10 mGy and 496 mGy·cm), breast and axilla (13 mGy and 526 mGy·cm), breast DIBH (10,60 mGy and 809 mGy·cm), 4D lung (30,70 mGy and 2423 mGy·cm), lung SBRT (39,90 mGy and 2141 mGy·cm), and prostate (15,10 mGy and 717 mGy·cm). As a future perspective, it is important to expand the sample, integrate image quality assessment criteria, and make comparisons with other dose calculation tools. It is also worth highlighting the potential to estimate the risk associated with exposure from planning CT scans, in the future. The results obtained allow for a better understanding of local acquisition practices in RT planning CT, reinforce the importance of periodic evaluation of protocols, and highlight the relevance of radiation protection and safety in clinical practice. Furthermore, they constitute a starting point for the implementation of optimisation strategies and the definition of DRL.
Description
Keywords
Tomografia Computorizada de Planeamento Radioterapia Avaliação de Doses nos Órgãos Níveis de Referência de Dose Software NCICT Planning Computed Tomography Radiotherapy Organ Dose Assessment Dose Reference Levels NCICT Software