Exploring the unique role of PETCT in clinical practice

Introduction: When we encounter suspected recurrence or metastasis on the road to fighting cancer, facing high-tech medical examination methods, should we choose PET-CT examination? PET/CT plays its unique role in clinical practice.

First, for patients with known tumors, PET/CT can be used to:

1. Clinical staging of tumors. PET/CT can not only observe the morphology, structure, and activity characteristics of the tumor itself, but its whole-body scanning feature can obtain the relationship between the tumor and surrounding tissues and organs at one time, whether there is peripheral invasion, lymph node or distant site metastasis, and make a more complete tumor staging, providing a basis for formulating more efficient treatment plans.

2. Evaluate the degree of differentiation and prognosis of malignant lesions. Different tumors have different biological characteristics. Even tumors of the same pathological type will have different biological metabolic characteristics reflected in PET imaging due to their specific differentiation. Tumors with different differentiation will also respond differently to treatment, with different effects. PET/CT can assist in more refined evaluation of the different degrees of differentiation within the tumor and make a preliminary judgment on the prognosis of treatment.

3. Find the primary site of metastatic tumors. The discovery of some tumor diseases often stems from the symptoms of metastatic lesions, while the symptoms of the primary site are very hidden. In clinical practice, it is common to see patients who first develop neurological symptoms due to brain metastasis, or first develop pain due to bone metastasis. PET/CT can use whole-body scans to find the location of unknown or hidden primary tumors.

4. Assist in making refined decisions on comprehensive tumor treatment plans. On the basis of the aforementioned determination of staging and primary lesions, assist clinical oncology, surgery, pathology and other departments to jointly formulate reasonable comprehensive treatment plans and make refined decisions.

5. Determination and positioning of biological target areas for radiotherapy. When radiotherapy is needed, the target area is traditionally determined based on the tumor structure imaging area of ​​CT or MRI. However, the activity range of the tumor does not completely match the structural range. For example, in the case of atelectasis caused by lung cancer, or necrosis without tumor components inside the tumor, the range of tumor activity determined by PET is actually smaller than the abnormal structure range seen by CT or MRI. In this case, PET can be used to determine the biological target area for radiotherapy and reduce unnecessary medical radiation dose.

6. Early prediction and evaluation of treatment efficacy to guide timely modification of treatment plans. After the start of tumor treatment, the effect of treatment needs to be evaluated in a timely manner; although the structure of some lesions has not yet subsided, the activity has been significantly reduced or even disappeared, indicating that the treatment plan is effective; however, if the treatment response is poor or even the lesions progress, it is necessary to change the treatment strategy or plan in a timely manner, or assist with other effective treatment methods.

7. Differentiation between tumor remnants and fibrous tissue formation or necrosis after treatment. Some tumors will have residual fibrosis, necrosis, and scar structures after treatment. PET can help identify whether the residual structures have residual tumor activity or whether there are signs of recurrence.

Secondly, for patients with suspected tumors or those at high risk of tumors, PET/CT can be used

1. Unexplained abnormal increase in tumor markers. People often find abnormal increase in tumor markers during physical examinations. After routine examinations and observations, the abnormality of tumor markers cannot be explained. It is necessary to find out whether there is a hidden primary tumor. At this time, PET/CT can be used to find the location of the tumor with the help of the sensitivity area of ​​tumor active lesions.

2. Screening of high-risk groups for cancer. We do not recommend PET/CT for "high-end physical examinations" for the general population, because its tumor detection rate for the general population is not higher than that of routine physical examination screening; but for high-risk groups with a family history of cancer, when they reach the high-risk age group for the corresponding cancer, PE/TCT examinations can be considered as appropriate on the basis of completing basic physical examinations.

3. Guide the precise biopsy site of suspicious lesions. Clinically, some patients have already found lesions suspicious of tumors, and further biopsy is needed to clarify the pathology. However, if there are non-tumor components such as necrosis and inflammation inside the lesions, biopsy of these parts may cause false negative results. PET/CT can determine the site of tumor activity in the lesion and accurately point out the location suitable for biopsy. In addition, for lesions with multiple metastases, PET/CT can select biopsy sites with less trauma and more accurate conclusions.

Again, PET/CT can be applied to blood system diseases. PET/CT is widely used in lymphoma, and there are detailed application recommendations in clinical guidelines. It plays a vital role in the baseline evaluation and staging before lymphoma treatment, the early and mid-term efficacy evaluation after treatment, and the efficacy evaluation after the end of treatment. For leukemia, it can be used to find extramedullary infiltration lesions of leukemia and evaluate the treatment effect. For other blood system diseases, such as plasma cell diseases such as multiple myeloma, etc., it can also be used for staging and efficacy evaluation.

PET/CT is most commonly used in the nervous system for: localization diagnosis of epileptic foci, preoperative evaluation and efficacy evaluation; early diagnosis, differential diagnosis and course evaluation of Alzheimer's disease; diagnosis and differential diagnosis, grading, and identification of recurrence of brain tumors; evaluation of brain function related to brain trauma, cerebrovascular lesions, mental illness, brain infection diseases, drug addiction and abuse, alcoholism, etc.; research on brain physiological functions and cognitive functions.

PET/CT is commonly used in the cardiovascular system to: determine myocardial ischemia, infarction, and survival; and evaluate the efficacy of coronary revascularization.

In addition, other applications of PET/CT include: finding fever-causing lesions for fever of unknown cause and analyzing the comprehensive connection of systemic lesions; and diagnosing difficult-to-identify systemic diseases, such as atypical tuberculosis, various nonspecific infections, and various immune-related diseases.

In short, as an important weapon in molecular imaging, PET/CT has specific functions in many aspects.