Mechanism of Cancer in Positron Emission Tomography

This article discusses the current uses of Positron Emission Tomography (PET) in understanding the mechanism of cancer. It also highlights the challenges and limitations of PET and compares it with Magnetic Resonance Imaging (MRI). The article emphasizes the importance of optimal quantification in PET scanning and its clinical applications. The study material is relevant for students pursuing courses in medical imaging, nuclear medicine, and oncology.

Running head: MECHANISM OF CANCER IN POSITRON EMISSION TOMOGRAPHY
Mechanism of cancer in Positron Emission tomography
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MECHANISM OF CANCER IN POSITRON EMISSION TOMOGRAPHY
Current uses of PET in purpose of understand mechanism of cancer:
As mentioned above, PET is a novel diagnostic or assessment technique which is
being abundantly used in the detection and identification many acute and chronic diseases in
the present, especially cancer. As discussed by Ziai et al. (2016), position emission
tomography can be considered as one of the most rapidly growing sectors of medical
imaging, which has gained recognition across the globe as an efficient diagnostic assessment
along with being an aid which helps radically in deciphering of the mechanism of cancer
development in the body. On a more elaborative note, the most notable or principal goal of
utilization of this particular assessment technique is to visualize, measure, and characterize
the different biological processes at the cellular, subcellular, and molecular levels in living
subjects using non-invasive procedures (Catana, Guimaraes and Rosen 2013). The PET
imaging techniques performs optimal utilization of the traditional imaging techniques and
with the novel infrastructural and technological innovations, introduces positron-emitting
probes. These probes helps in the determination of the expression of the indicative molecular
targets with respect to different stages of cancer progression. Furthermore, with
fluorodeoxyglucose which has been used abundantly in the PET scanning for staging and
restaging cancer progression, FDG has also been widely used in the treatment response
evaluation and differentiation of post-therapy alterations from residual or recurrent tumour,
along with prognosis assessment as well. Hence, it can be easily stated that this particular
nuclear medicine technology assisted diagnostic technique has a multipronged applicability in
the cancer management (Ehrhardt et al. 2014).
The metabolic biomarkers have become core components or advanced nuclear
medicinal health assessments and treatment techniques. The past decade has witnessed a
thorough revolution of the health care techniques which in turn is helping or aiding in the
process of improving not just the disease management, but is also changing the scenario for

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disease detection and improving the quality of life for the hundreds of individuals who are
coping with a certain acute or chronic disease. The PET scan or imaging continues to be one
of the most significantly useful techniques in the early detection of the exact metabolic
changes which are aiding in the process of disease progression with respect to cancer. Roach
et al. (2018) have described PET technology to be a non- invasive imaging technique which
in turn detects the presence of gamma rays which is released from a positron-emitting
isotope, which in turn has a variety of impacts on the diagnosis and treatment of the disease.
The PET scan or the result from the imaging technique helps the clinicians to view
and assess the human body from a biochemical and functional perspective, a thorough
assessment for detecting cancer for a patient. As a highly sensitive and accurate nuclear
medicine imaging technology based on molecular biology, PET has a unique ability to assess
the functional and biochemical processes of the body's tissues, which are altered in the
earliest stages of virtually all diseases (Moore et al. 2018). In this context, it has to be
mentioned that cancer has a radiating impact on the body, which changes the metabolic and
physiological processes of the human body drastically. The PET scan is able to detect the
minutest of anomalies in the metabolic and physiological processes of the body, even before
an anatomical or structural change can manifest itself. The commercial utilization of the PET
imaging had been introduced in the year of 2001, in combination with CT scan, PET imaging
has provided major advancements in the detection of primary tumours, distant metastases,
and recurrence after treatment, and for staging, restaging, and even monitoring therapy
response in most cancers (Deroose et al. 2017).
Particular challenges:
One of new and novel techniques for cancer disease management is the position
emission tomography, or PET. By definition, PET can be characterized as a nuclear medicine
functional imaging technique which helps in the observing and detecting the anomaly or

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abnormality in the metabolic processes of the body which in turn helps in the detection of any
disease processes existing in the body of the patient. Although, PET scanning is a renowned
technique in the process of detection and diagnosis of cancer and other major diseases, this
increasingly popular assessment technique is also associated with certain challenges and
limitations (Rowe et al. 2016). First and foremost, it has to be understood that PET imaging
techniques uses a radioactive tracer to detect the differences between healthy and diseased
tissues, hence, there are certain risks associated with the use of radioactive tracer. First and
foremost, even though the exposure to radiation is low and short lived when a patient is taken
for PET imaging, the amount is still enough to cause damages to the normal body processes.
Along with that, the radioactive tracer or marker can also expose considerable radiation to the
foetus of a pregnant woman or to the infant of a woman who is breastfeeding.
Another notable challenge of PET imaging technique is the possibility of the patient
developing allergic reaction to the radioactive tracer which will hinder the successful
implementation of the assessment technique. With respect to clinical usage, limitation to the
widespread use of the PET scan includes very high cost of cyclotrons, which is used to
produce the short lived radionuclides. Specially adapted on-site chemical synthesis apparatus
to produce the radiopharmaceuticals after radioisotope preparation can also be challenging to
obtain in different clinical settings. Along with that, the authors have described the fact that
the organic radiotracer molecules which are generally specifically adapted with on-site
chemical synthesis apparatus in order to produce radiopharmaceuticals after radioisotope
preparation can also be fairly challenging in remote settings. Furthermore, only few hospitals
and clinical research centres have the capacity or infrastructure to maintain such systems.
Most of the clinical PET is supported by third-party suppliers of radiotracers that can supply
many sites simultaneously, which restricts the availability of PET scanners to hospitals with
hot labs only. Lastly, the half-life of fluorine-18 is about two hours and the dose prepared

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having this radionuclide undergoes multiple half-lives of decay through one full working day,
which in turn mandates frequent recalibration of the remaining dose and careful planning
with respect to patient scheduling, to optimally utilize the technique (Marner et al. 2017).
Quantification:
Optimal quantification also has a huge role in the successful identification of the PET
scanning and identification of the developmental anomalies within the body of the patient. It
has to be mentioned in this context that the quantification of the fluorodeoxyglucose or FDG
uptake during the scanning procedure has a multipronged clinical application, especially in
cancer diagnosis and staging. First and foremost, dedicated FDG PET/CT-based visual and
quantitative criteria is developed to assess and evaluate the treatment response to a significant
extent. Along with that, the extent or amount of tumour FDG uptake has been attributed to
reflect the biologic aggressiveness of the tumour, which in turn predicts the risk of metastasis
and recurrence (Joshi et al. 2015). Although the FDG uptake levels can be measured using
qualitative, semi- quantitative, and quantitative methods, the quantification provides maximal
accuracy.
Moreover, Volumetric FDG uptake measurements such as metabolic tumour volume
and total lesion glycolysis have shown substantial promise in providing accurate tumour
assessment, which cannot be availed without optimal quantification of the data. Another very
effective quantification technique is the SUV or Standardized uptake value measurements
which is quantified using maximum, mean, or peak levels. Although it has to be
acknowledged in this context that most of the quantification techniques including the SUV
measurements are associated with and can be effected many technical, physical, and biologic
factors. Therefore, there is need for enhanced familiarity among the nurses and clinicians
with the FDG uptake quantification techniques, both their benefits and pitfalls (Brenner,
Wedel and Eary 2018).

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PET VS MRI in understanding mechanism of cancer:
Both positron emission tomography or PET and Magnetic resonance imaging or MRI
are abundantly used imaging techniques being used in the clinical practice to detect acute and
chronic diseases including cancer. Although both techniques are used abundantly in the
identification of cancer or other similar deliberating disorders, there are severe
differentiations between of the both conditions which is needed to be discussed in detail. First
difference between both techniques includes the details of the technique itself used, whereas
PET scanning uses radioactive tracers to detect anomaly within the tissues of the body, the
MRI uses magnetic fields and radio waves which helps in obtaining detailed images of the
organ anomaly which is noticed (Queiroz et al. 2015). Along with that, author have described
that one major obstacle to PET in or near an MRI is the presence of the magnetic field, which
cause gain changes and spatial distortion in photomultiplier tubes (PMTs), the scintillation
light detector of choice for PET scanners.
Along with that, MRI scanning takes a longer while to get completed, ranging from
30- 45 minutes per area, whereas, PET scanning procedure is fairly quick, which only
occupies 5- 10 minutes per area. Although, a notable distinction between both procedures
includes the radiation risk or threat which is prominent in case of the PET scan and is none in
case of the MRI. Similarly, there are also certain differences in the soft tissues and bony
structure assessment of the images obtained. Whereas soft tissues are presented with higher
details in the MRI scans than what is provided in the PET scan images, the bony structure is
represented in much higher details for the PET scans as compared to the MRI imaging.
Although, it has to be mentioned that for cancer or tumor detection, PET scan continues to be
the best available technique, outperforming MRI imaging due to the high sensitivity to
metabolic or structural changes in the body that occurs during metastasis (Bailey et al. 2015).

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