What is the best way to evaluate clinical target volume for radiotherapy of brain tumors?

Abstract

475 ISSN 2045-0907 10.2217/CNS.13.49 © 2013 Future Medicine Ltd CNS Oncol. (2013) 2(6), 475–477 Over the last few decades, the goal of understanding dosing and protection of surrounding normal tissue during radiotherapy (RT) has improved. To date, technological development in RT has been focused on achieving a better definition of the tumor/target to increase the therapeutic efficacy. Volume definition (for targets and organs at risk [OAR]) is essential for the success of RT treatment planning, where it plays a crucial role in the complete eradication of the disease without toxic effects on healthy tissue. Computed tomography (CT) remains the only imaging modality used for dose calculation in RT treatment planning, despite the existence of other imaging modalities, such as MRI and PET, which are important in the detection of the target. Several studies have analyzed the importance of the definition of tumors and OAR [1–6], and the impact of various CT slice thicknesses on the identification of clinical target volume (CTV) has been assessed in terms of volume and dose reconstruction algorithms for RT planning [7,8]. However, all of the RT processes are based on CT, so slice thickness affects not only the CTV, but also OAR definition, quality of reconstructed images in all planes (sagital, coronal and axial), digitally reconstructed radiographs, treatment planning system beam’s-eye view and the dose–volume histogram. Moreover, as RT techniques are more sensitive to geometric uncertainties due to their sharper dose gradients around the target volume and OAR, or severe hypofractionations, such as intensity-modulated RT (IMRT), stereotactic RT or brachytherapy, the volume definition becomes much more important [9,10]. The Photon Treatment Planning Collaborative Work Group recommended a CT slice thickness in the range of 3–5 mm for the head and 5–10 mm for the body to obtain an accurate definition of the inferior and superior borders of the CTV, this suggests that further studies in the CT slice thickness optimization are required [11]. A CT scanner has the availability of different slice thicknesses (from oneto several millimeters); it is, therefore, useful to choose the optimum slice thickness for treatment planning based on the tumor localization, with respect to the treatment purpose (palliative or curative). Larger slice thickness may miss part of the considered