Application in Clinical Outcomes and Prediction of Prognosis. Clinical Trial
Official title:
Radiotherapeutic Tumor Response and Normal Tissue Effect in Treating Thoracic Malignancy : as Comparing With Free-breathing Non-gating Methods.
Technologic advances in the field of radiation oncology have made in possible to deliver a
highly conformal and accurate radiation dose to a target tissue. Accompanying the rapid
implementation of these novel techniques is often a reduction in the radiation margins,
which reinforces the importance of accurate target delineation, and reduces the side effect
of therapy.
F-18 FDG PET/CT is widely used in oncology, including complete whole body staging, restaging
and monitoring of tumor response in different types of cancers. As to non-oncology
application, inflammation in almost any tissue will result in increased FDG accumulation.
However, the normal tissue with sparing radiation may show subtle change, and would be
difficult to be detected. FDG PET/CT was limited in the spatial resolution of 5 mm and low
FDG-avid disease. To be evaluation of the interval change of metabolic response before and
after radiotherapy of thoracic malignancies, we plan to initiate a prospective study trail
the takes advantages of recent technical advances of technique in 4-dimensional PET/CT (4-D
PET/CT) with respiratory gating system.
Respiratory motion creates artifacts in PET and PET/CT images, and can alter diagnosis. The
tumor edge would be blurred due to respiratory movement, and be underestimated the uptake
value. Also, semi-quantitative measurement, standard uptake value (SUV), combined with
parameters such as the lesion site and shape, which is commonly used to make the final
assessment of disease would be mis-estimated.
The study aims to investigate the correlation of 4-D PET/CT with respiratory gating methods
and free breathing PET/CT when processing primary thoracic malignancy and normal tissue
effect.
Radiation pneumonitis is the dose-limiting toxicity in thoracic radiotherapy (RT) for
thoracic malignancy. It occurs beginning after the initiation of RT for up to 6 months
characterized by cough, shortness of breath, and changes in lung function. A mortality rate
approaches 50% in severe radiation pneumonitis [4]. Dosimetric parameters, such as the
percentage of lung volume irradiated ≧20 Gy (V20) and the mean lung dose (MLD), provide a
guide to assess the risk of radiation pneumonitis in the treatment planning process.
However, the parameters have poor predictive power for individual risk. The appearance of
radiation lung injury shown in computed tomography (CT) was characterized by and early and a
late phase. Since, radiation pneumonitis is characterized by the migration of leukocytes
from the blood to irradiated lung tissue; thus, on FDG-PET imaging, more intense
inflammatory responses will result in greater FDG uptake. Identifying an early sign or
precursor of normal tissue damage helps predicting the delayed organ dysfunction.
In combined PET/CT, CT is used for localization and correction for attenuation in the PET
images. An accurate spatial registration of PET and CT image sets is a prerequisite for
accurate diagnosis and SUV measurement. However, because of respiration, and the difference
in the acquisition time required to image the thorax between PET (6-9 minutes) and CT (~15
seconds), spatial misalignment between the 2 image sets is not uncommon. This misalignment
significantly compromises the interpretation of PET images, resulting in mislocalization of
the lesion and inaccurate quantitation of the SUV. The main cause of these artifacts is the
dynamic interaction between transaxial image acquisition and the asynchronous motion of
tumor and normal tissues. To account for motion effects, respiratory gating techniques have
been developed.
A more sophisticated respiratory-motion monitoring system is the Real-Time Position
Management respiratory gating system (RPM). The system includes a video camera that measures
respiratory motion by tracking the vertical displacement of 2 infrared reflective markers
rigidly mounted on a plastic block placed on the patient's thorax. The motion of the block
is displayed by a graphical interface on the RPM workstation. It has been used in gated
radiotherapy of lung, respiratory-gated CT, and 4-D CT, as well as respiratory-gated PET
imaging.
We plan to enroll patients with thoracic cancer who scheduled further radiotherapy. Patients
with pre-existing chronic lung disease, such as COPD, interstitial lung disease, cystic lung
disease, et al, will be excluded. The FDG PET/CT will be performed before the radiotherapy
(baseline study), and 30-45 days after completing radiotherapy (2nd study). Free-breathing
whole body scan will be performed after 40 minutes, and regional 4D PET/CT with RPM method
for chest was performed subsequently. These patients will be follow-up in radiation oncology
clinics, any radiation-related adverse effect and long-term prognosis will be recorded. The
association between the data analysis will be further investigated.
We will obtain better delineation of the correlation and the differences between
free-breathing PET/CT 4-D PET/CT with RPM respiratory-gating methods in processing tumor
metabolism, more over, to assess normal tissue metabolic effect. And the further work is
trying to find if the application helps in clinical outcomes and prediction of prognosis of
the technique of 4-D PET/CT with RPM respiratory-gating methods.
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Observational Model: Case Control, Time Perspective: Prospective