The use of PET/CT in radiotherapy planning: contribution of deformable registration

INTRODUCTION Medical imaging provides information for diagnosis and staging, evaluation of treatment response, and also plays pivotal role in advanced radiotherapy treatment planning. In the era of the innovative conventional and functional imaging techniques, the main goal of radiation therapy, which is to maximize the dose to the target while minimizing the dose to adjacent healthy organs, can be actualized. On the basis of this, accurate delineation has led to the safe decrease of radiotherapy volumes, in terms of resulting in a reduced risk of normal tissue toxicity, and increasing tumor control probability (De Ruysscher et al., 2005; van Der Wel et al., 2005). Computed tomography (CT) is the primary modality for image-based treatment planning, but conventional anatomic imaging with CT has limited sensitivity to identify distinctly the anatomic borders of the tumor (Nestle et al., 2009). Integration of multimodality imaging data for radiotherapy treatment planning is beneficial and indespensable for perfect delineation (Kessler et al., 1991; Rosenman et al., 1998). Currently, several studies showed that positron emission tomography–computed tomography (PET/CT) is significantly used for staging for various type of tumor. PET/CT combines biological activity and anatomical information in a single study session, and provides to distinguish viable tumor focus. The use of PET/CT for fused images with planning CT (pCT) may allow adequate tumor visualization (De Ruysscher et al., 2005; van Der Wel et al., 2005). Otherwise, implementation of PET/CT information for radiation therapy planning (RTP) to accurate delineation is under investigation, but is not recommended for a routine procedure. In this paper, we focus on the clinical adoption of PET/CT and the use of PET/CT in RTP.