Pet Diagnostic Test – A Comparison of the Positives and Negatives of It in Oncology


It can be safely said that the medical field has wholeheartedly embraced the PET scan test. The invention of computerized axial tomography has increased the popularity of PET even more. PET CT test had forever altered the way lymphoma is staged and consequently treated. This especially true for the kinds that can be potentially cured, for example:

classical Hodgkin’s lymphoma

large cell or aggressive lymphoma

When viewed in just Hodgkin’s and non-Hodgkin’s lymphoma, PET scans are literally universal. They have been adopted for treatment worldwide and even transformed the way we perceive care given during these conditions.

A Comparison with Traditional Test

One of the earlier tests used in oncology were gallium scans. Today, they have been wholly replaced by PET scans because the latter are:

extremely convenient

highly sensitive

Furthermore, PET CT imaging is capable of revealing the condition even when the lymph nodes are average in size. In gallium scans, this was considered as of no consequence. This sensitivity is one reason why PETs are commonly used during the staging of the disease.

A Different Approach to Treatment

It is not just the testing phase that has seen a paradigm shift due to the technology, even the way healthcare practitioners approach treatment of lymphoma has changed. Take for example large masses that are often seen as scar and residual mass even after being sterilised of the condition. If a traditional method of diagnostic is utilised, it is near impossible to discern if the residual mass has an active form of the disease or not.

The consequence of a conventional test is further irradiation to treat the mass even when a biopsy proves it to be scar tissue because there could be a sampling error. With PET the thought process has reformed, if there are no apparent active cancer cells in the mass irradiation is not given.

Another area where treatment of cancer has been altered is a genuinely negative PET scan. After the completion of therapy, if the scan is entirely negative, it is considered that the disease has gone into remission. The statistics of relapse occurring after a negative PET imaging is in single digits. Additional data and analysis show that a response seen in a PET scan after 2 to 3 cycles of chemotherapy is even more dependable, prognostically, as compared to one that is taken when therapy finishes.

As a result, in classical Hodgkin’s lymphoma and large cell lymphoma cases, an early stage trial has begun that is considering if it is advantageous to alter therapy based on the results of an interim PET scan.

Caution Should Be Practiced

For those who have been diagnosed with lymphoma, PET technology was Godsend. But like any other tool we use, there is a need for caution. Some parts of PET scan are still unclear such as:

What constitutes a negative study and what a positive is still indistinct.

Which assessment is more precise – eyeball or the semiquantitative SUV scores?

In the case of semiquantitative SUV scores, at what level of SUV activity should the test represent negativity?

Besides these unanswered questions, there are issues like the difficulty with which data from one PET machine gets transferred to another. There is no standardisation of the time between the injection of radioisotope and the measurement of the activity. The difference can affect the result of the scan. Moreover, lymphoma is not the only condition that results in a positive scan. Infection, delayed infiltration of inflammatory cells and thymic rebound, all can show up in pet scan oncology

The last but the most significant drawback of PET scans is their interpretation. Observers see different things on the same scan especially if there is a subtlety in the imaging. When the scan is crystal clear, as in unambiguously positive or negative, diagnosis is the same by all viewers. When there are grey areas, the interpretation of the scan may change with the viewer.

What Can be Answered in the Future

It has been seen that a positive scan after or halfway through chemotherapy is a prediction of treatment failure. If this turns out to be a fact, then researchers need to find out if an alternative therapy would prove more beneficial. The decision can be substantiated with biopsy results. Finding the answer to this can:

Spare a patient an ineffective and painful treatment

Give the patient to try a different measure that might show positive effects

Determine if the positive scan was the consequence of drug resistance

Another area that needs to be though over is the number of chemotherapy cycles when interim PET scan is negative. The tradition is six cycles with two given after complete remission. But if the imaging comes out to be negative, is it possible to lessen the number of chemotherapy treatments. This can be thought over because data shows that relapses far and few in between when PET is negative.

The Hope Is Strong

Despite the difficulties and in spite of the answered questions, there is no denying that PET scans are the best technology for detecting lymphoma. They make a significant advancement in the care given to cancer patients and will remain so for a long time.