Dados do Trabalho

Título

TECHNICAL ASPECTS OF COMPUTED TOMOGRAPHY APPLIED IN IMAGING DIAGNOSIS AND RADIATION THERAPY

Introdução

Computed tomography (CT) can be used for diagnosis (CTD) and for radiotherapy planning (CTRP), due to the excellent differentiation and resolution of tissues with the acquisition of three-dimensional images. In planning radiotherapy, it is essential to correctly determine and optimize the dose distribution in the planning target volume (PTV) and the organs at risk (OAR's) around the radiation field. Knowledge about CT techniques and their specificities regarding their application modalities: CTD or CTRP, is an essential requirement for a correct diagnosis and for an effective radiotherapy plan.

Objetivo

The aim of this study was to differentiate the main image acquisition techniques used in CTD and CTRP.

Método

Tomographic exams obtained with protocols for diagnostic use and protocols adapted for radiotherapy planning in a 16-channel multislice equipment were compared.

Resultados

The studies showed that the CTD examination table is cushioned, while for CTRP a rigid and perfectly flat plate is required, coupled to the examination table, so that the tomographic images conform to the calculation algorithms of the TPS (Treatment Planning System). The accessories used in the positioning for the CTD prioritize the patient's comfort and symmetry, in CTRP the accessories have as main objective the guarantee of daily reproducibility in the treatment. The selection of field of view (FOV) in CTD is made according to the study region, while in CTRP a larger FOV is needed, which encompasses a margin beyond the patient's body surface. The thickness and spacing between the cuts used in the most common CTD vary between 0.5 to 2.0 mm, in CTRP usually cuts from 3.0 to 5.0 mm are used. The reconstruction windows in CTD are essential to evaluate the different tissues, in CTRP only the soft tissue window is enough. The use of contrast in CTD is of great importance, whereas, in CTRP, it is not so used, but, when requested, it usually consists of only one contrast phase. Another distinction is that in CTD, chest and abdomen exams are performed with the patient in apnea, while in CTRP this does not apply, as it is not possible to guarantee reproducibility during treatment.

Conclusão

In view of the different requirements for the operation of a tomography, knowledge and differentiation between CTD and CTRP are essential for the necessary protocol adaptation.

Palavras-chave

computed tomography; diagnosis; radiotherapy planning.

Área

Radioterapia