Functional Imaging for Radiation Treatment Planning, Response Assessment, and Adaptive Therapy in Head and Neck Cancer,福建省肿瘤医院 郑德春 博士,Role of routine and functional Imaging (FI),Screening and diagnosis of neoplasms Precise staging of malignancy Response assessment of cancer treatment Monitor recurrences,Benefit of FI,Major modalities of FI: positron emission tomography (PET) combined with CT or magnetic resonance (MR) imaging fMRI: DWI, DCE-MRI, BOLD, spectroscopy etc. Emerging techniques: PET-MRI, DKI, IVIM, APT, CEST etc. Offer complementary information including metabolism of FDG, proliferation, hypoxia, and cell membrane synthesis by PET hypoxia and permeability by DCE MRI and IVIM, cell proliferation and apoptosis by DWI, IVIM and DKI, and epidermal growth factor receptor status.,About this article,Part I: Discusses the practical aspects of integrating functional imaging into head-and-neck radiation therapy planning. Part II: Reviews the potential of molecular imaging biomarkers for response assessment and therapy adaptation. Authors concluded that FI allowed more individualized treatment planning in patients with head and neck SCCs in the emerging era of personalized medicine.,Part I Role of Functional Imaging in Radiation Therapy Planning,There was a 20% decrease in OS among patients who underwent radiation therapy with a protocol that did not comply with established institutional standards. Reasons:Inaccuracies in tumor target delineation Inter-observer variability in clinical practice based on CT for target delineation Functional MRI and PET techniques provide different and potentially complementary information about the tumor extent and biologic activity.,PET-based Tumor Target Contouring,Tumor uptake of PET radioactive tracers can provide excellent contrast resolution between neoplastic and normal tissues. There are two DOSE CONTOURING methods: visual interpretation and automated delineation methods.,Example of automated delineation,Figure 2. SCC arising from the epiglottis (T2N2bM0) in a 67-year-old man. Axial fused FDG PET/CT image shows tumor contours automatically generated with diagnostic software by using percentages of the maximum SUV (20%, 30%, 40%, and 50%) and a fixed SUV cutoff of 2.5.,Automated delineation is believe to be more objective than visual delineation. Because, an alteration of the SUV scale can change the apparent tumor volume and lead to increased inter-observer variability.,Status of PET-contouring at present,At present, there is no consensus regarding the optimal contouring method. The most practical approach to defining the tumor target is to rely on expert visual interpretations by nuclear medicine physicians and radiologists And rely on knowledge of the likely patterns of disease infiltration within strict SUV scale limits. However, limited spatial resolution and partial volume effects blur the edges of FDG-avid tumors at PET.,PET-based Radiation Therapy Planning,the FDG PETdefined gross tumor volume (GTV) was found to be smaller and more accurate than the CT- or MR imagingdefined GTV and closer to the tumor volume at pathologic analysis. however, no single imaging modality allowed perfectly accurate three-dimensional estimation of the tumor volume. All modalities failed to detect about 10% of the tumor volume, mainly because of superficial tumor extension. PET was found to allow the identification of potential disease extension beyond the CT-defined GTV in 29%64% of cases.,PET-based Radiation Therapy Planning,Duprez et al (24) demonstrated the feasibility of applying dose escalation to an FDG PETavid GTV with dose painting by numbers instead of with GTV contouring. The use of multimodality imaging raises the question of whether the GTV should be defined on the basis of imaging with only one or with several modalities？ The lack of concordance found between various imaging modalities suggests that the safest approach when defining a target is to use all imaging modalities along with physical examination. Anatomic and functional imaging modalities could provide different but complementary information during contouring and planning for cancer RT treatment.,Contour lines are color coded to show the imaging modality on which they are based (green = CT, blue = MR imaging, orange = PET).,Adaptive Radiation Therapy Planning,There is considerable interest in personalizing treatment in an attempt to optimize the therapeutic ratio for individual patients. One avenue for achieving this is to alter the delivery of radiation therapy on the basis of changes in the tumor and/or normal organs during a course of treatment. Mainly current radiation therapy is planned at a single pretreatment time-point to delineate the target volume and any organs at risk, with no account taken of anatomic changes during the course of fractionated radiation therapy.,Adaptive Radiation Therapy Planning,Geets et al showed reductions of 51% in the clinical target volume and 48% in the planning target volume after a partial course (45-Gy dose) of radiation therapy. In a subsequent study of patients receiving CRT therapy for laryngopharyngeal cancer , PET-based and CT-based primary tumor GTVs were found to decrease at a mean rate of 3.2% and 3.9% per treatment day, respectively while nodal GTVs decreased at a rate of 2.2% per treatment day. In addition, positional shifts were noted in the GTV.,