Trial Information

Can PET CT Coregistration Imaging Adequately Determine the Gross Tumor Volume and Microscopic Extension in Non-Small Cell Lung Cancer Patients for Radical Radiation Therapy?

Radiation therapy is an important component in the curative treatment of non-small cell lung
cancer. Targeting of the gross tumor has been facilitated by the use of CT simulation
allowing for more accurate delineation of the tumor. In addition multi-modality imaging
combining functional and anatomical information have allowed for further refinement in the
treatment planning process with significant impact on the planning target volume due to the
addition of PET imaging information. PET using 18 F-fluorodeoxyglucose (FDG) allows for
more precise detection of tumor since it is a functional image based on glucose metabolism
rather than structural abnormalities. Biochemical changes often precede any gross
anatomical abnormalities, therefore making PET a very powerful imaging modality. FDG PET
has been shown to be more sensitive and specific than CT in the staging of NSCLC.Radical
radiation therapy is indicated for early stage NSCLC when the patient is medically
inoperable primarily due to co-morbidities. In contrast for locally advanced NSCLC, radical
radiation is used as part of induction therapy or in the definitive treatment of NSCLC. In
order to avoid a geographical miss with precision radiation therapy, the gross tumor volume
(GTV) is outlined and a margin around the GTV is added to incorporate microscopic extension
of disease, also known as the clinical target volume (CTV). Standard margins of 1.0 to 1.5
cm are used to encompass the gross tumor, microscopic extent and treatment setup
uncertainties.There is surprisingly very little data on what constitutes an adequate margin
to encompass the microscopic extent around the gross lung tumor. Studies involving
conformal radiation therapy and dose escalation in NSCLC have primarily used an empirical
margin to define the CTV. A literature review revealed only two studies evaluating the
ability of CT to define the gross tumor and its microscopic extension correlated with
histopathological measurements [P Giraud et al 2000, R Chan et al 2001]. The two studies
have produced conflicting results with recommended margins being from zero mm to 6-8 mm
around the GTV. There have been no studies evaluating the ability of PET to define the size
of the gross tumor and its microscopic extension.This is a companion study to the two OCOG
PET trials in NSCLC. It will evaluate the ability of CT alone versus PET CT to define the
gross tumor and its microscopic extension. The methodology will be based on contouring the
GTV with imaging modalities of CT and PET CT and correlating the findings with
histopathology.This proposed study will add new information on the ability of combined PET
CT to determine the microscopic extension of tumor in NSCLC. While no imaging modality can
detect microscopic extension, the newer technology of PET CT may give better resolution over
CT alone in the detection of tumor. The strength of this proposal is the required
correlation with pathological findings. If PET CT is able to accurately determine the
extent of disease, this will have major implications on treatment volumes and subsequent
targeting for radiation therapy using 3D conformal radiation therapy.