Imaging
Summary of Key Points
• Noninvasive medical imaging often is essential to cancer management at multiple times in the course of the illness.
• Imaging currently is used for screening to detect cancer, characterize lesions, perform locoregional and systemic staging, provide prognostic information, assess response during and after therapy, restage after treatment, perform follow-up of patients for recurrence, and precisely guide biopsies and therapies such as external beam or systemic radiation, brachytherapy, or thermal and other ablations.
• More invasive interventional radiologic procedures also can guide and monitor vascular or intraluminal delivery of treatments such as radioactive microspheres, embolic materials, radiofrequency or cryoablation, and therapeutic drugs.
• Imaging methods range from the traditional anatomic methods—radiograph, computed tomography (CT), and ultrasound—to the more functional methods of magnetic resonance imaging (MRI) and nuclear medicine methods, including positron emission tomography (PET), single photon emission computed tomography (SPECT), and planar nuclear imaging. Hybrid methods combining PET and CT, SPECT and CT, and PET and MRI are growing in importance. Optical imaging is promising but is limited by penetration of light through tissues to superficial structures in most cases.
• Plain films and mammography remain useful techniques, with mammography (including digital mammography) being the main imaging method that has been clearly proven capable of reducing cancer deaths when applied in the screening setting.
• CT remains the cornerstone technology for most oncologic imaging, and CT technology that allows for rapid-sequence angiography is finding new applications, as is three-dimensional reconstruction of CT data sets. Screening data with CT-colonography continues to improve, and in some studies it has been found to be comparable with traditional colonoscopy for colon cancer screening. CT scanning for lung cancer screening appears to be capable of reducing lung cancer death rates when applied to high-risk populations. The radiation dose from CT is a concern, and major efforts to reduce this dose from CT scanning have been implemented in newer CT systems.
• MRI is the imaging tool of choice for central nervous system, spinal, and musculoskeletal neoplasms, as well as for assessing vascular and some hepatobiliary and pelvic lesions. MRI also can be used to detect breast cancers, especially in women with dense breasts. Concerns regarding gadolinium-associated nephrogenic systemic fibrosis have led to cautions in the use of MRI contrast medium in patients with impaired renal function. Newer MRI techniques such as diffusion imaging and complement diffusion contrast MRI appear promising in assessing response to tumor treatment.
• Bone scans using single-photon methods (e.g., technetium-99m methylene diphosphonate) remain the dominant procedure for detecting suspected bone metastases; however, the PET agent fluorine-18 sodium fluoride is increasingly being applied. These techniques may be less sensitive for marrow involvement than MRI and other PET techniques for detecting bone metastases of many tumors.
• PET and PET/CT technology using 18
