One of the questions most frequently asked by patients diagnosed with prostate cancer is: “Has the disease spread to another part of the body?” Answering this question forms the basis of both treatment planning and the monitoring process. In situations where conventional imaging methods cannot always give a sufficient answer to this question, different approaches in the field of nuclear medicine come into consideration. Foremost among these is the PET/CT method known as Ga-68 PSMA imaging.
What Is Ga-68 PSMA, How Does It Work?
PSMA is the abbreviation of the expression “Prostate-Specific Membrane Antigen”. This protein is a structure that can be found at a much higher level on the surface of prostate cancer cells compared to healthy prostate tissue. In Ga-68 PSMA imaging, this feature is made use of: a special molecule labelled with Gallium-68, a radioactive substance, shows a tendency to bind to the PSMA protein.
After this labelled molecule is given to the patient intravenously, it can show accumulation in cells with a high PSMA level. The PET/CT device, by converting this accumulation into an image, provides simultaneous information about both the anatomical structure and the metabolic activity. The basic logic of the method is based on making a molecular feature of the tumour visible.
There is an important nuance here: PSMA expression may not be at the same level in every prostate cancer cell. For this reason, the imaging results are interpreted together with other clinical and pathological findings. It is addressed not as a definitive diagnostic tool on its own, but as a supporting part of the clinical assessment.
What Is the Difference Between Ga-68 PSMA and Conventional PET/CT?
In the standard PET/CT examinations widely used in oncology, a radiopharmaceutical called FDG (fluorodeoxyglucose) is generally used. FDG accumulates in cells showing high metabolic activity and can provide valuable information in the imaging of many cancer types.
However, some prostate cancer cells may not give a signal at the expected level in FDG-based imaging. This can create an important limitation, particularly in clinical scenarios where it becomes difficult to determine where the disease is progressing with biochemical findings such as a rise in PSA. Ga-68 PSMA imaging, thanks to its targeting mechanism specific to the PSMA protein, aims to offer a different layer of information in these scenarios.
Both methods have their own advantages and limitations. Which imaging approach is suitable is evaluated according to the clinical characteristics of the disease and the clinical question being asked.
In Which Situations Can It Be Taken Into Assessment?
In which clinical scenarios Ga-68 PSMA imaging can come into consideration is addressed within the framework of certain criteria in international oncology guidelines and nuclear medicine guidelines. It is not applied routinely in every patient; suitability is determined separately in the clinical assessment process.
Staging of High-Risk Prostate Cancer
After a prostate cancer diagnosis is made, evaluating the extent of the disease is a critical step in treatment planning. Particularly in cases accepted as high-risk, the investigation of lymph node involvement or the presence of distant metastasis may be required. In this staging process, Ga-68 PSMA PET/CT can be evaluated by clinicians as an option that can offer additional information to conventional imaging methods.
<34 class=”text-text-100 mt-2 -mb-1 text-base font-bold”>Biochemical Recurrence Investigation
The PSA level beginning to rise again after prostate cancer treatment is called biochemical recurrence. In this picture, determining where the disease is active can be decisive in terms of subsequent treatment decisions. In situations where conventional imaging methods are insufficient, particularly at low PSA values, Ga-68 PSMA imaging is among the methods that can come into consideration in the investigation of active disease foci.
<34 class=”text-text-100 mt-2 -mb-1 text-base font-bold”>Monitoring the Response to Treatment
Evaluating the effectiveness of the treatments applied is an inseparable part of oncological monitoring. In some clinical scenarios, Ga-68 PSMA imaging can be evaluated as a helpful tool in monitoring the changes during the treatment process. Which monitoring method is applied when is determined according to the patient’s clinical condition and the treatment protocol.
Lutetium-177 PSMA Treatment Planning
PSMA-targeted radioisotope treatments are among the treatment approaches that can be evaluated in certain patient groups. For such treatments to be able to be planned, the presence of sufficient PSMA expression in the tumour may need to be revealed in advance through imaging. In this context, Ga-68 PSMA imaging can function as a preliminary step in determining treatment suitability.
How Does the Application Process Work?
The Ga-68 PSMA PET/CT examination is an imaging application carried out by nuclear medicine units. The labelled substance is applied intravenously before the examination, and imaging is carried out after a certain waiting period. The total process is generally completed within a few hours; this period covers the application of the radiopharmaceutical, the waiting period needed for accumulation and the imaging stage.
Some preparations may be requested from the patient before the examination. These preparations may differ according to the protocol applied and the individual’s clinical condition. All preliminary information regarding the examination is shared by the nuclear medicine team that will carry out the procedure.
The dose of the radioactive substance used during imaging is determined within the framework of international standards. The radiation exposure is evaluated together with its contribution to the clinical decision-making process, and the application is planned for patients deemed suitable.
How Are the Results Interpreted, What Does It Mean if the Image Shows Nothing?
The interpretation of Ga-68 PSMA PET/CT results is a process carried out in collaboration between the nuclear medicine and oncology branches. The detection of a signal in the images may point to the presence of foci with high PSMA expression; however, this finding does not give a definitive result in the pathological sense on its own and should be addressed together with other clinical data.
An important incorrect expectation is this: not seeing a signal in the image is not definitive proof that there is no disease. Tumours with a low PSMA expression level may not give a sufficient signal in imaging. Different diagnostic approaches can come into consideration for such “PSMA-negative” situations. The findings should always be evaluated together with the clinical picture, the course of PSA and other imaging data.
What Is the Relationship Between Ga-68 PSMA and Lutetium-177 Treatment?
Clinicians and patients can from time to time confuse these two concepts with each other. Ga-68 PSMA is an imaging method; it is used for diagnostic and staging purposes. Lutetium-177 PSMA, on the other hand, is a treatment approach that makes use of the same PSMA targeting mechanism but is labelled with a different radioisotope.
The relationship between the two can be summarised as follows: Ga-68 PSMA imaging can help to reveal whether a sufficient PSMA target is present in the tumour. This information can be of the nature of a preliminary step in the planning of PSMA-targeted treatments such as Lutetium-177 PSMA. However, the detection of a signal in imaging does not automatically mean that a switch to Lutetium treatment will be made; both decisions require separate clinical assessment.
Frequently Asked Questions
Is Ga-68 PSMA imaging performed in every prostate cancer diagnosis?
No, it is not applied routinely in every case. Which staging or monitoring method is used is determined in line with the risk of the disease, the PSA values and the clinical characteristics. The oncology team makes this assessment individually.
Can this examination be recommended even though my PSA value is low?
Yes, in some clinical scenarios it can come into consideration even at low PSA values. Particularly when a suspicion of biochemical recurrence needs to be investigated at an early stage, this method can offer different information compared to conventional imaging. Suitability is evaluated by the clinician.
If no signal appears in the image, is this a good sign?
“No signal” does not always mean “no disease”. Some tumours with low PSMA expression may not be imaged sufficiently with this method. The results are interpreted together with the course of PSA and other clinical data. For this reason, discussing the result together with the oncology team instead of evaluating it on its own is important.
Is treatment also carried out in the same session as Ga-68 PSMA?
No. Ga-68 PSMA is an imaging application; it is not used for treatment purposes. Treatment-oriented radioisotope applications (for example, Lutetium-177 PSMA) require a different preparation process and clinical assessment; they are planned within the scope of a separate protocol.
Is this examination also used in other cancer types?
The PSMA protein is predominantly associated with prostate cancer. Although PSMA expression has also been reported in some other tumour types, the clinical use in these areas is being evaluated within the scope of research. In current clinical practice, the method is predominantly used in prostate cancer-focused scenarios.
When are the results ready?
The reporting time of the examination completed on the imaging day can vary according to the centre where it is applied and the complexity of the examination. After the report is prepared, evaluating the results together with the oncology team is important in terms of the correct interpretation of the findings in the clinical context.
This text is for general information purposes and does not replace a medical assessment. Whether Ga-68 PSMA imaging is applied in your situation is planned by the physician team together with the stage of the disease, the course of PSA and the clinical findings. For your questions regarding whether Ga-68 PSMA imaging can be evaluated in your clinical picture, you can get information through drhasanmorcali.com.
