Imaging Techniques
Computed Tomography (CT), also known as CAT scanning (Computerized Axial Tomography), utilizes X-rays to generate detailed cross-sectional images of the body. By combining data from several X-ray images taken from different angles, CT creates comprehensive two-dimensional images of bones, blood vessels, and soft tissues in a single slice. The resultant images provide more detailed information than conventional X-rays, allowing for better analysis and thus diagnosis.
Contrast agents are crucial in enhancing the diagnostic capabilities of imaging techniques such as Computed Tomography (CT). These agents help to improve the visibility of internal organs, blood vessels, and tissues, making it easier to distinguish between normal and abnormal structures. Most commonly used contrast agents in CT scans are iodine-based. These agents are preferred because iodine has a high atomic number, which effectively blocks X-rays, thus enhancing the contrast in the images. There are also barium-sulfate compounds used primarily for examining the gastrointestinal tract. Each type of contrast agent is chosen based on the specific area of the body or the type of examination required. Iodine-based agents are ideal for angiography because they clearly delineate blood vessels against surrounding tissues.These agents help in identifying and defining the boundaries of tumors because they often accumulate more in vascularized tumor tissues than in normal tissues. When administered, iodine-based contrast agents increase the electron density within the tissues or vessels where they distribute. This higher electron density enhances the X-ray attenuation, causing the areas with contrast to appear much brighter on the resulting images. This makes it easier to visualize fine details and subtle differences that might indicate disease.
Contrast agents can be administered in various ways depending on the specific diagnostic requirements and the part of the body being examined. The most common method for CT scans is intravenous (IV) injection, where the contrast agent is directly injected into a vein. This method is particularly useful for enhancing images of blood vessels and internal organs such as the liver and kidneys, as well as for highlighting tumors. For examinations of the gastrointestinal tract, patients may be asked to drink a solution containing a contrast agent. This oral administration helps to clearly outline the stomach, intestines, and other parts of the GI tract. In some cases, particularly for detailed images of the lower gastrointestinal tract, the contrast may be administered rectally. Although less common, intra-arterial administration involves injecting the contrast directly into arteries; this technique is used for specific types of vascular imaging where detailed views of arterial structures are required
Magnetic Resonance Imaging (MRI) relies on strong magnetic fields and radio waves to generate detailed images. MRI excels in soft tissue imaging, tumor detection and characterization, and treatment monitoring in oncology. The advantages of MRI include no radiation exposure, excellent soft tissue contrast, and multiplanar imaging capabilities. However, MRI has longer scan times and is contraindicated for patients with certain metal implants. Specialized MRI techniques such as diffusion-weighted imaging, perfusion imaging, and spectroscopy provide additional diagnostic information.
Positron Emission Tomography (PET) uses radioactive tracers to visualize metabolic activity in tissues. In oncology, PET is crucial for cancer detection, staging, treatment response monitoring, and recurrence detection. The most common tracer used is FDG (fluorodeoxyglucose), which images glucose metabolism. PET's advantages include its ability to show functional information and detect cancer before structural changes occur. However, it has limitations such as lower spatial resolution, radiation exposure, and potential false positives due to inflammation. PET is often combined with CT (PET/CT) for better anatomical correlation.
In the field of oncology research, patient preparation for each imaging modality is a crucial step to ensure accurate and reliable results. Understanding the basic principles of image interpretation allows healthcare professionals to effectively analyze and utilize the data obtained from these imaging techniques. Safety considerations and contraindications must always be at the forefront, as they help prevent potential risks and ensure patient well-being during imaging procedures. Nurses play a vital role in this process, providing essential patient education and care throughout the imaging process. Their involvement ensures that patients are well-informed and comfortable, which contributes to the overall success of the procedure. Furthermore, integrating imaging results into oncology research protocols is essential for advancing our understanding of cancer and developing new treatments. By combining imaging data with clinical and laboratory findings, researchers can gain comprehensive insights into the disease, leading to more effective and personalized therapeutic approaches.
Tumor Staging
The TNM system is a fundamental tool in oncology for staging cancer, providing a standardized method to describe the extent of a patient's cancer. In this system, T represents the primary tumor, N denotes the involvement of regional lymph nodes, and M indicates the presence or absence of distant metastases. The T category describes the size and/or extent of the primary tumor, typically ranging from T0 (no evidence of primary tumor) to T4 (most advanced stage). The N category assesses the degree of spread to regional lymph nodes, usually ranging from N0 (no regional lymph node involvement) to N3 (extensive regional lymph node involvement). The M category is typically binary: M0 indicates no distant metastasis, while M1 signifies the presence of distant metastasis.
Oncology nurses should understand that TNM classifications can be clinical (cTNM), based on physical examination, imaging, and biopsies before treatment, or pathological (pTNM), determined by examining tissue removed during surgery. The TNM system is periodically updated to incorporate new research findings, and different cancer types may have specific TNM criteria. Nurses should also be aware that additional factors, such as grade (G) or serum tumor markers (S), may be incorporated into the staging for certain cancers. The TNM classification is ultimately used to group cancers into overall stages (usually I to IV), which guide treatment decisions and provide prognostic information. Understanding the TNM system is crucial for oncology nurses as it forms the basis for treatment planning, patient education, and interdisciplinary communication in cancer care.
Response Evaluation Criteria (RECIST)
RECIST terminology classifies lesions as either measurable or non-measurable and as either target or non-target. Measurable lesions are those that can be quantitatively assessed according to specific criteria (detailed below). From the measurable lesions, target lesions are selected to be monitored throughout the patient's treatment course. Once designated as a target lesion, it remains a target even if its size falls below the baseline limits for measurable lesions.
By re-evaluating a specified number of these defined lesions in subsequent scans, the patient's disease burden can be classified as improving, stable, or progressive.
Eligibility
In oncology research, the response evaluation criteria stipulate that only patients with measurable disease at baseline should be included in protocols where objective tumor response is the primary endpoint. Measurable disease is defined as the presence of at least one measurable lesion. If the measurable disease is limited to a solitary lesion, its neoplastic nature should be confirmed by cytology or histology. Measurable lesions are those that can be accurately measured in at least one dimension with a longest diameter of at least 20 mm using conventional techniques or at least 10 mm with a spiral CT scan. Non-measurable lesions include all other lesions, such as small lesions (longest diameter less than 20 mm with conventional techniques or less than 10 mm with a spiral CT scan), bone lesions, leptomeningeal disease, ascites, pleural/pericardial effusion, inflammatory breast disease, lymphangitis cutis/pulmonis, cystic lesions, and abdominal masses not confirmed and followed by imaging techniques.
All measurements should be recorded in metric notation, using a ruler or calipers. Baseline evaluations should be performed as close as possible to the beginning of treatment and no more than four weeks before treatment starts. The same method of assessment and technique should be used to characterize each identified and reported lesion both at baseline and during follow-up. Clinical lesions are considered measurable only when they are superficial, such as skin nodules and palpable lymph nodes. For skin lesions, documentation by color photography, including a ruler to estimate the size of the lesion, is recommended.
Methods of Measurement​
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CT and MRI are the best currently available and reproducible methods to measure target lesions selected for response assessment. Conventional CT and MRI should be performed with cuts of 10 mm or less in slice thickness contiguously. Spiral CT should be performed using a 5 mm contiguous reconstruction algorithm. This applies to tumors of the chest, abdomen and pelvis. Head and neck tumors and those of extremities usually require specific protocols.​
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Lesions on chest X-ray are acceptable as measurable lesions when they are clearly defined and surrounded by aerated lung. However, CT is preferable.
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When the primary endpoint of the study is objective response evaluation, ultrasound (US) should not be used to measure tumor lesions. It is, however, a possible alternative to clinical measurements of superficial palpable lymph nodes, subcutaneous lesions and thyroid nodules. US might also be useful to confirm the complete disappearance of superficial lesions usually assessed by clinical examination.
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The utilization of endoscopy and laparoscopy for objective tumor evaluation has not yet been fully and widely validated. Their uses in this specific context require sophisticated equipment and a high level of expertise that may only be available in some centers. Therefore, the utilization of such techniques for objective tumor response should be restricted to validation purposes in specialized centers. However, such techniques can be useful in confirming complete pathological response when biopsies are obtained.
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Tumor markers alone cannot be used to assess response. If markers are initially above the upper normal limit, they must normalize for a patient to be considered in complete clinical response when all lesions have disappeared.
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Cytology and histology can be used to differentiate between PR and CR in rare cases (e.g., after treatment to differentiate between residual benign lesions and residual malignant lesions in tumor types such as germ cell tumors).​
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Target Vs. Non-Target Lesions
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At baseline, all measurable lesions, up to a maximum of five lesions per organ and ten lesions in total, representing all involved organs, should be identified as target lesions. These target lesions must be recorded and measured at baseline. The selection of target lesions should be based on their size, specifically those with the longest diameter, and their suitability for accurate repeated measurements, whether by imaging techniques or clinical examination. The sum of the longest diameters (LD) for all target lesions will be calculated and reported as the baseline sum LD. This baseline sum LD will serve as a reference for characterizing the objective tumor response.
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All other lesions or sites of disease should be identified as non-target lesions and recorded at baseline. Although measurements of non-target lesions are not required, the presence or absence of each lesion should be noted throughout the follow-up period.
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Response Criteria
Evaluation of target lesions
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Complete Response (CR): Disappearance of all target lesions
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Partial Response: At least 30% decrease in the sum of the LD of target lesions, taking as reference the baseline sum LD
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Progressive Disease (PD): At least a 20% increase in the sum of the LD of target lesions, taking as reference the smallest sum LD recorded since the treatment started or the appearance of one or more new lesions
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Sta le Disease (SD): Neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, taking as reference the smallest sum LD since the treatment started
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Evaluation of non-target lesions
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Complete Response (CR): Disappearance of all non-target lesions and normalization of tumor marker level
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Incomplete Response/Stable Disease (SD): Persistence of one or more non-target lesion(s) or/and maintenance of tumor marker level above the normal limits
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Progressive Disease (PD): Appearance of one or more new lesions and/or unequivocal progression of existing non-target lesions