Diagnosis and treatment of cancer frequently requires imaging to perform essential tasks. Imaging is used for detection, localization, and characterization of tumors - important tasks in diagnosis. Guidance or navigation, orientation, monitoring and evaluation are important steps that employ imaging in therapy. Medical imaging modalities are used to acquire the data needed to accomplish these tasks - radiography, fluoroscopy, x-ray computed tomography, positron emission tomography (PET) and single photon emission computed tomography (SPECT), ultrasonography, and magnetic resonance imaging.
In this chapter, the use of imaging in diagnosis and treatment of solid tumors is summarized. The principal emphasis is on current imaging technologies and image processing methods used to extract information that can guide and monitor interventions after cancer has been detected, leading to the initial diagnosis and staging.
The process for detection, diagnosis and treatment of cancer is illustrated in Fig. 18.1. One or many imaging examinations may be done at each step, and various modalities may be used depending on the specific cancer type, site, extent, and other factors.
For many solid tumors, as distinguished from leukemia which may not be associated with a well-defined mass, the imaging tasks are outlined in Fig. 18.2. Cancer is often detected, even when unsuspected, on a routine chest x-ray or screening examination, such as a mammogram. Once detected, it is important to localize the mass using imaging, especially when it is small. A biopsy procedure may be done under image guidance, leading to characterization of a suspicious mass and confirmation of malignancy. If the biopsy is negative, the lesion may be considered benign. In many cases, no further treatment is needed for a benign process.
If a malignancy is present, it is invariably treated. There are often several options, and sometimes different treatment modalities are used in combination. Among the options, the most common treatment methods are chemotherapy, surgical resection, and radiation therapy. The surgical and radiotherapy approaches require guidance to reach the mass, especially if it is small or near critical structures. Navigation is often done using computer-aided systems which instantaneously provide orientation data so that the surgeon, for example, can understand the relationship between a surgical instrument and nearby structures. Finally, treatment delivery is done, such as in radiation therapy, by depositing radiation to the tumor while minimizing the dose to adjacent structures. Imaging is used in the planning, execution and follow-up of these interventions.
Each imaging modality - radiography, computed tomography (CT for x-ray; SPECT for gamma emitting isotopes), magnetic resonance imaging (MRI), positron emission tomography, and others - provide complementary information. The same body region is often studied by several modalities to better understand the anatomy and function of a solid tumor and adjacent structures (Fig. 18.3).
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