وصف
PET and CT scans are medical imaging techniques that are used to diagnose and monitor a wide range of medical conditions. PET scans use a radioactive tracer that is injected into the patient's bloodstream. This tracer accumulates in the body's tissues, and the PET scanner detects the emitted radiation to create a 3D image of the body's metabolic activity. CT scans use X-rays to create detailed images of the body's internal structures. The scanner rotates around the patient, capturing multiple images from different angles, which are then reconstructed into a 3D image. PET-CT scans are commonly used to diagnose and monitor cancer, as cancerous cells typically have higher metabolic activity than healthy cells, making them more visible on the scan. They are non-invasive and do not typically require anesthesia. The patient may need to fast before the scan or avoid certain medications to ensure accurate results. They are generally safe, but they do expose the patient to radiation. The amount of radiation is small and considered safe for most patients
ملخص
- PET CT is a fusion of biological (PET) and anatomical (CT) imaging, offering a more comprehensive view compared to individual scans. CT provides morphological information, while PET focuses on metabolic activity. This combination yields better results in diagnosing and managing head and neck cancers.
- In head and neck cancers, PET CT is used for several key purposes, including detecting unknown primary tumors, TNM staging, identifying synchronous primary tumors, assessing therapy response, detecting recurrence, and radiotherapy planning. It's especially helpful in cases where the primary tumor location is unknown, identifying it in approximately 30% of patients.
- For unknown primary carcinomas, PET CT can guide biopsy sites. If initial physical examinations, endoscopy, and MRI are negative, PET CT is recommended. Negative PET CT results require consideration of surgical biopsies. A positive PET CT warrants panendoscopy and frozen section biopsies.
- PET CT provides information on the primary tumor, nodal metastasis, distant metastasis, and potential second primary carcinomas. Studies have shown it to be more sensitive than MRI and CT in detecting the primary tumor, with limitations in T staging when dealing with small submucosal lesions or perineural spread.
- Metastatic lymph nodes in ipsilateral and contralateral sides decrease survival rates significantly. PET CT aids in detecting bilateral neck metastasis, improving prognosis and treatment planning. It has higher sensitivity and specificity compared to CT or MRI alone in detecting cervical lymph node metastasis.
- PET CT detects distant metastasis in about 25% of patients, commonly in the lungs, mediastinal nodes, bone, and liver. It can identify malignant lesions that may not be visible on CT or MRI alone, such as early marrow metastasis. Finding distant metastasis changes the treatment approach from localized to systemic.
- PET CT can detect synchronous primary tumors, which occur in approximately 8% of head and neck cancer patients due to risk factors like drug abuse. Common synchronous primaries are found in the lungs, head and neck, and esophagus.
- PET CT improves prognostic stratification by distinguishing between curative and palliative care categories. It plays a vital role in radiotherapy planning by reducing inter-observer variability in Gross Tumor Volume and possibly increasing it. PET CT-guided radiotherapy can lead to better treatment outcomes.
- PET CT is crucial in assessing the response to treatment. It's recommended 4-6 weeks after chemotherapy and 12-16 weeks after radiotherapy. While it has a high negative predictive value, a negative PET CT scan can confidently indicate the absence of disease. The Hopkins criteria are used for reporting PET CT results in head and neck cancers.
- PET CT is helpful in detecting recurrent diseases. Guidelines like NCCN recommend PET CT for initial staging of oral cavity, oropharynx, and hypopharynx cancers. It is considered for Stage 3 and 4 diseases and mucosal melanomas, especially N2 and N3 nasopharyngeal cancer. PET CT is essential for post-treatment evaluation.
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