The Use Of PET/CT In Prostate Cancer

Prostate cancer can be a deadly disease among men, especially in cases where the illness is not localized to the prostate gland. The condition is also common in the male population.

The American Society of Clinical Oncology reports that prostate cancer is the second most common cancerous disease among men. It is estimated that 191,930 male patients will be diagnosed with prostate cancer in 2021. The disease is most common in men over 65, representing 60% of all the cases related to prostate cancer. 

Conventional imaging tests are often used to assist in the detection of prostate cancer. This may include a bone scan or a CT scan. Recent studies show that more accurate and sensitive testing procedures may be possible by switching to positron emission tomography. The use of PSMA PET CT scan options is growing in popularity and even recent official recognition and approval recently. 

We take a closer look at the role of a PET scan in diagnosing both localized and metastatic prostate cancer in this post. We also consider current options that are available with this new technology, including the use of prostate-specific membrane antigen testing procedures. 

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What Is A PET Scan?

A PET scan is an advanced imaging test that is used in different medical departments. The primary purpose of a PET scan is generally to assist in detecting disease in a patient’s body. The scan does not work independently, as special tracers are needed to provide accurate results during the procedure. The procedure is also known as a positron emission tomography scan. 

The tracers used during a PET scan are radioactive. The reason for the tracers’ radioactive function is to help the doctor see how the tracers are distributed throughout the body. These tracers also contain a special type of dye. The use of the dye allows the PET scan to show a doctor exactly where the tracers are in the body. 

The purpose of this procedure is to help doctors determine how certain tissues in the bodywork. Doctors can usually use the imaging test to determine a poor functioning organ or tissue that has problems. 

In men with prostate cancer, PSMA expression will be elevated in affected areas. It has been found that the expression tends to be significantly higher in prostate cancer cells and a prostate tumor, compared to tissues in the area that are unaffected by cancer. 

When a patient undergoes a PET scan, they will usually do so at an outpatient center. If a hospital is utilized, the patient will generally not need stay overnight or be admitted. Once the test is finished, the patient can leave the hospital. The doctor who performed the test will closely analyze the results obtained and provide the patients with details on their findings. 

PET scans are very common. Approximately two million scans happen every year in the United States. The worldwide figure would be even greater. 

How Does It Work?

On the patient’s side, a PSMA is a relatively simple procedure. The patient will not be taken to the surgery hall, as this is not a surgical procedure. In most cases, patients do not need to be put under anesthetics. 

The first step is for the healthcare provider to place PSMA tracers inside the patient’s body. Without these tracers flowing through the body, the PET scan would not yield useful results. The tracers’ dyes and radioactive design help the doctor identify areas of disease in the patient’s prostate gland and pelvis. 

Three methods can add the tracers to the bloodstream. A patient may need to drink a liquid solution. Sometimes, they need to inhale a vapor. Both of these are effective techniques for administrating the tracers. There are also cases where healthcare providers inject the tracers directly into the patient’s bloodstream. This can help to ensure the tracers are visible in less time. 

Some time may pass between the imaging procedure and the administration of the tracers. Once enough time has passed, the patient is pushed into a large device that performs the PET scan. 

In patients with prostate cancer, the scan will be targeted at the pelvis area. If metastasis is suspected, the PET imaging test may be focused on the entire body. This would allow the doctor to identify specific sites where cancer has spread toward. The idea behind the tracers is that they will start to accumulate in areas where there is a high level of chemical activity.

Some diseases, including cancer, will cause cells to have an elevated level of chemical activity. When there is a bright spot that shows up on the scan, it generally means the tracers are accumulated in that specific area. In cases where these spots show up in the prostate gland, it may indicate cancerous cells’ presence. 

Reasons a doctor may use a PET scan

There are three specific reasons why a doctor may decide to use a PET scan to assess a patient who has been diagnosed with prostate cancer. These reasons include:

  • The doctor wants to see if the cancer is spreading to other tissues in the surrounding area or other parts of the body. 

  • The doctor wants to check up on the treatment the patient is receiving. The test helps the doctor determine if the treatment is working. If the treatment does not seem to be shrinking cancer, adjustments can be made to provide more effective results. 
  • Doctors can also turn to PET scans to see if there is a recurrence of cancer. If the patient is suspected of experiencing a recurrence, the doctor may book them for regular PET scans. 

While these are the current primary reasons for PET scans and PSMA to be used in patients with prostate cancer, more advancements are likely to be made. As technology advances, doctors might start to implement the PSMA imaging tests in more stages of cancer. The goal here would be to reduce the risk of cancer spreading while also targeting areas that are likely to suffer a recurrence. 

Who Are Good Candidates For PSMA?

The use of PSMA and a PSMA tracer in patients with prostate cancer is still a relatively new option. Conventional imaging tests are generally used in the detection of prostate carcinoma. Doctors often also utilize conventional tests to find pelvic lymph nodes and bone metastases. These procedures are generally followed by radiotherapy and other appropriate treatment options. 

Due to the fact that PSMA is still new and only recently received approval, there are currently limitations in the areas it is used. In current studies, two specific groups of patients with prostate cancer are considered eligible for the use of these imaging procedures. 

Below, we provide an overview of patient populations that current studies focus on:

Recurrent Occurrence Of Prostate Cancer

Early treatment of prostate cancer often yields a positive prognosis. There are several cases where the patient is cured of prostate cancer, especially in cases where the tumor is localized to the prostate gland. Some patients, however, may experience a recurrence of cancer

If a patient experiences a recurrence after prior successful treatment, then a PSMA may be a useful option. This imaging test will offer doctors a more accurate view of the prostate gland – allowing them to determine specific sites of possible metastasis or where the recurrence is developing. A more targeted treatment method may then be used, such as to provide radiation therapy that focuses on the specific area identified through the PSMA PET. 

High-Risk Prostate Cancer Patients 

A patient with high-risk prostate cancer will be more likely to experience an advanced level of the disease. These are also the patients at the greatest risk of experiencing metastasis. When metastasis occurs, the cancerous cells spread to other parts of the body. This increases the complications associated with the disease and leads to a higher risk of mortality. 

In these cases, a PSMA test may be useful. Conventional imaging tests are often unable to detect the areas of metastasis at an early age. The tracers used in a PSMA test can help to provide a more accurate overview of the affected site. This also means the doctor has a better chance of detecting where metastasis may occur. 

Targeted therapy can then be aimed at this site. The removal of these tumorous parts prior to metastasis may help to prevent complications. 

What Are The Benefits?

There are certain advantages for PET scans, particularly in comparison to conventional imaging tests. The primary benefit that PET scans have over options like MRI and CT scans is the fact that the procedure offers a molecular imaging system. This means the images that on the screen have details that go down to a cellular level. When the patient has a prostate tumor or even distant metastases, these diseases are related to the tissues’ cellular structure. MRI and CT scans may fail to present these on the screen. 

A PET scan’s higher sensitivity provides further benefits for patients at risk of prostate cancer and those who have high-risk prostate cancer. 

In addition to these advantages, it is important to note that problems can often be detected at an early stage with a PET scan. It is well-known that early diagnosis of cancer – especially advanced cancer that is metastatic – is critical. The overall survival chances of the patient can significantly enhance.

In recent times, healthcare providers have combined PET scans with other imaging technologies to provide even more advanced detection methods. In particular, CT scans. 

A CT scan takes advantage of X-ray technology. The technology can produce images that represent the interior organs and tissue of the patient’s body. People generally refer to a PET CT scan as an image fusion. There are also cases where healthcare providers combine PET scans with MRI imaging tests. A special computer program will combine the imaging test results from both the CT and the PET scan. 

What Are The Risks Of PET Scans?

When looking at PET scans, one of the first things people may notice is the fact that radioactive particles are administered into their bodies. Radioactivity links with a large number of adverse reactions. With this in mind, we should take a look at the potential risks that may be associated with a PET scan. 

First, it is important to realize that the level of radiation in these tracers is exceptionally low. Most experts state that the radiation contained within the tracers will not cause harm to the human body. The tracer is made from glucose mostly. Radioactive compounds then attach to the glucose molecules. This formulation ensures the body can quickly and effectively dispose of the tracers. 

However, it’s worth noting that some patients experience allergic reactions to the tracers used for a PET scan. These tracers usually contain small amounts of saccharin, aspartame, and iodine. Individuals who are allergic to any of these compounds should ensure they mention this to the doctor. Injecting tracers that contain these compounds could lead to serious allergic reactions. 

Additionally, patients with certain diseases may also not be good candidates for PET scans.

The tracers that use iodine may lead to adverse reactions in patients with the following conditions:

  • Cardiovascular disease

  • Asthma

  • Sickle cell anemia

  • Kidney disease

  • Multiple myeloma

  • Polycythemia vera

There are alternative dyes and tracer substances that can be used. Doctors need to be aware of any diseases in the patient prior to deciding which tracer will be used. 

The Future Of PSMA PET-CT

The FDA only approved the use of PSMA PET-CT scans and a new drug application for this procedure on the 1st of December, 2020. The application for this approach to the diagnosis and management of prostate cancer was submitted through a collaboration between multiple entities, including:

  • The University of California, San Francisco (UCSF)

  • The University of California, Los Angeles (UCLA)

It should be noted that this approval is for the use of Ga-PSMA-HBED-11. This type of agent is used alongside a PSMA PET procedure and may be utilized to assist with the management of prostate cancer. 

Currently, the entities that developed the procedure have not yet announced their plans to make the new drug application public. We still need more studies on the subject. Thus, we do not know when we will be able to use these new applications in medical facilities. 

At the moment, however, we know that the use of a PET scan as a method for gaining more detailed information on prostate cancer is a viable option. The use of these imaging methods among patients with prostate cancer is likely to increase in the near future. There is also a likeliness that we will see a significant increase in the number of studies conducted on the topic.

Following extensive research and further investigation, the method may receive official approval for use in medical facilities throughout the world. Additional drug applications could also be made, now that there is sufficient evidence suggesting the efficiency of PET scans in the diagnostics of metastatic prostate cancer. In the future, we may be able to combine the technology with additional techniques.

Combining different technologies may help provide even more accurate targeting of areas that are most likely to experience metastasis. Once the technology becomes implemented as a standard for monitoring patients with recurrent or metastatic prostate cancer, the medical industry will likely improve the prognosis. Early-stage detection of metastasis becomes more accurate with the use of these technologies. By detecting prostate cancer early on, new areas can be targeted through treatment. Therefore, this may eliminate the cancerous cells before the disease becomes systematic. 

Conclusion

The recent approval of PSMA PET imaging procedures for diagnosing and monitoring prostate cancer has created a revolution in the medical industry. The FDA has provided clearance for the use of a drug application, also known as an NDA, used in combination with PSMA PET. Following this approval, more research will likely go into this management option for prostate cancer patients. 

While we still need further studies, current evidence shows positive effects and a lot of potential for the use of PSMA in men with recurrent prostate cancer. The high sensitivity also makes this an ideal option among men with suspected prostate cancer metastasis

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Sources

  1. Cancer.Net. (2020) Prostate Cancer: Statistics. [online] Available at: https://www.cancer.net/cancer-types/prostate-cancer/statistics#:~:text=Prostate%20cancer%20is%20the%20most,of%20diagnosis%20is%2066%20years.
  2. SNMI. Prostate-Specific Membrane Antigen (PSMA). [online] Available at: http://www.snmmi.org/Patients/Procedures/Content.aspx?ItemNumber=13981
  3. SNMI Value Initiative. (2020) Information You Need to Know on New PSMA PET Landscape. [online] Available at: https://www.snmmi.org/Research/Content.aspx?ItemNumber=35274
  4. BMC. PSMA-PET for individualized radiation therapy of prostate cancer. [online] Available at: https://www.biomedcentral.com/collections/PSMA
Alternative Text

Dr. Ahmed Zayed

Dr. Ahmed Zayed holds a baccalaureate of Medicine and Surgery. He has completed his degree at the University of Alexandria, Egypt. Founder of ZayedMD, Dr. Ahmed believes in making the knowledge as accessible as possible to patients. He had his work featured in reputable publications such as The Huffington Post. Other than his passion for writing, Dr. Ahmed spends​ his time outside the hospital at the gym or with a good book.

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