Applying PET/MR in Oncology - a Prospective Project

Overview

Cancer is a global health issue. According to the World Health Organization, Cancer is the second leading cause of death globally, and is responsible for an estimated 9.6 million deaths in 2018. In Israel, more than 30,000 new cases of cancer were diagnosed, and more than 11,000 deaths were cancer-related during 2016. Imaging plays a pivotal role in cancer management, and multiple techniques are used in all phases of cancer management. The overall morphological, structural, metabolic and functional information obtained in imaging is used for improved individualized therapy planning. Different imaging modalities are available during different time points in the natural history of different malignancies: Early detection of cancer through screening based on imaging is probably a major contributor to a reduction in mortality for certain cancers . Once a diagnosis is made, determining the clinical stage of cancer, meaning the extent of the disease before any treatment is given, is a critical element in determining appropriate treatment based on the experience and outcomes of groups of previous patients with similar stage . Precise clinical staging of cancer is crucial. Not only that this clear non-ambiguous description is a key factor that defines prognosis, it is also a chief component of inclusion, exclusion, and stratification criteria for clinical trials. Several cancer staging systems are used worldwide. The most clinically useful staging system is the tumor, node, and metastasis (TNM) staging system developed by the American Joint Committee on Cancer (AJCC) in collaboration with the Union for International Cancer Control (UICC). The AJCC TNM system classifies cancers by the size and extent of the primary tumor (T), involvement of regional lymph nodes (N), and the presence or absence of distant metastases (M). There is a TNM staging algorithm for cancers of virtually every anatomic site and histology, with the primary exception of pediatric cancers. The clinical TNM (cTNM) classification should be used to determine correctly the clinical stage of cancer and to help guide primary therapy planning.

Stage may be defined at several time points during the monitoring period of cancer patients. When using imaging obtained during the relevant time frame, one may use one of the other TNM categories to stage correctly the cancer: For example, imaging is of high value in assessing therapy response during and after systemic and/or radiation therapy is given . Using imaging data and the clinical posttherapy TNM classification (ycTNM) is helpful in determining the patient's response to treatment. In case a patient is given the systemic therapy as a neoadjuvant therapy before a planned curative surgery, imaging may categorize the patient as a responder vs non-responder. If categorized as an early non-responder, another therapy or an upfront surgery may be advised, while eliminating therapy toxicity. If imaging, however, supports major response to treatment, more conservative treatment and avoidance of surgical intervention may be considered and change patients quality of life dramatically. In patients given a systemic therapy as a curative or a palliative therapy, assessing the response via imaging is crucial as well - if imaging studies support a progressive disease, changing therapy protocol is advised. In a disease controlled by the therapy, imaging may aid in guiding follow-up schedule, lifestyle and medical management. In the context of therapy response assessment, imaging is also important in assessing side effects of the therapy. Imaging may identify radiation-induced injuries, and may recognize pathologies associated with chemotherapy, biologic and immunotherapy. Imaging is also critical when recurrence of malignant disease is suspected. In such cases, when signs or symptoms suggest local recurrence, or when raised level of a tumor marker is documented, different imaging techniques can dramatically guide restaging of the disease using the recurrence-TNM classification (rTNM). In such cases imaging may localize the recurrent disease and may guide surgical/radiation/systemic therapy . Different imaging modalities allow assessment of virtually every cancer site and in every time frame during the continuum of the disease. Imaging aids in assessing tumor's size, location, and relationship to normal anatomic structures, as well as the existence of nodal and/or distant metastatic disease. Among the most commonly used imaging modalities are computed tomography (CT), magnetic resonance (MR) imaging, positron emission tomography (PET) and ultrasound. In addition to providing key information for assigning the T, N, and M categories, imaging is invaluable for guiding biopsies and surgical resections. PET imaging has revolutionized the imaging evaluation of cancer . By exploiting biochemical and physiologic differences between tumor cells and normal tissues , PET imaging has become