Molecular Imaging to Plan Radiotherapy and Evaluate Its Efficacy

Abstract

Learning Objectives: On successful completion of this activity, participants should be able to describe (1) how to acquire high-quality molecular images for use in radiation therapy; (2) how molecular imaging can be used to plan radiotherapy and evaluate treatment efficacy; and (3) the limitations and challenges to widespread use of molecular imaging in radiation oncology.Financial Disclosure: The authors of this article have indicated no relevant relationships that could be perceived as a real or apparent conflict of interest. CME Credit: SNMMI is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to sponsor continuing education for physicians. SNMMI designates each JNM continuing education article for a maximum of 2.0 AMA PRA Category 1 Credits. Physicians should claim only credit commensurate with the extent of their participation in the activity. For CE credit, SAM, and other credit types, participants can access this activity through the SNMMI website (http://www.snmmilearningcenter.org) through November 2018.Molecular imaging plays a central role in the management of radiation oncology patients. Specific uses of imaging, particularly to plan radiotherapy and assess its efficacy, require an additional level of reproducibility and image quality beyond what is required for diagnostic imaging. Specific requirements include proper patient preparation, adequate technologist training, careful imaging protocol design, reliable scanner technology, reproducible software algorithms, and reliable data analysis methods. As uncertainty in target definition is arguably the greatest challenge facing radiation oncology, the greatest impact that molecular imaging can have may be in the reduction of interobserver variability in target volume delineation and in providing greater conformity between target volume boundaries and true tumor boundaries. Several automatic and semiautomatic contouring methods based on molecular imaging are available but still need sufficient validation to be widely adopted. Biologically conformal radiotherapy (dose painting) based on molecular imaging-assessed tumor heterogeneity is being investigated, but many challenges remain to fully exploring its potential. Molecular imaging also plays increasingly important roles in both early (during treatment) and late (after treatment) response assessment as both a predictive and a prognostic tool. Because of potentially confounding effects of radiation-induced inflammation, treatment response assessment requires careful interpretation. Although molecular imaging is already strongly embedded in radiotherapy, the path to widespread and all-inclusive use is still long. The lack of solid clinical evidence is the main impediment to broader use. Recommendations for practicing physicians are still rather scarce. 18 F-FDG PET/CT remains the main molecular imaging modality in radiation oncology applications. Although other molecular imaging options (e.g., proliferation imaging) are becoming more common, their widespread use is limited ...

18F-FCho PET and MRI for the prediction of response in glioblastoma patients according to the RANO criteria

“…A 40% threshold of SUV max was applied because it corresponded best with the visually enhanced tracer uptake in the tumor. Moreover, it is well known that an automatic threshold technique is the best guarantee that consistent VOIs are defined on repeat scans as are acquired in our study [31,34]. Other advantages of automatic thresholding are that the method is user independent as well as independent of any changes in tumor geometry, which is of particular relevance in studies that assess therapy response because tumors may shrink as a result of effective treatments [35].…”

Hybrid positron emission tomography segmentation of heterogeneous lung tumors using 3D Slicer: improved GrowCut algorithm with threshold initialization

“…The inclusion of biological imaging may have the highest impact in the reduction of interobserver variability in target definitions. 2 Since the early 2000s, there has been a surge of PET-based automatic and semiautomatic contouring methods that have been proposed to help delineate the metabolic tumor activity. The methods range from simple to complex methods.…”

18F-Fdg-PET-guided Planning and Re-Planning (Adaptive) Radiotherapy in Head and Neck Cancer: Current State of Art

“…18 F-FDG is the most popular radio-tracer used in oncology and its use is increased also in patients treated with RT (16). Currently, some authors nearly considered 18 F-FDG PET/CT as a routine test in RT practice to contour target volumes (both primary tumor and metastatic lymph nodes) in patients with H&N carcinoma, decreasing inter-and intraobserver variability and increasing the conformity to real tumor boundaries (17,18).…”

“…18 F-FDG PET may be useful even as a prognostic factor due to the ability to early detect tumor recurrences (15)(16)(17)(18)(51)(52)(53)(54).…”