COMPARING BETWEEN RADIOTHERAPY PLANNING USING POSITRON EMISSION TOMOGRAPHY-COMPUTED TOMOGRAPHY (PET-CT) AND COMPUTED TOMOGRAPHY (CT) IN HEAD AND NECK

Objective: Conformal radiation therapy mandates accurate delineation of target volumes, which requires incorporation of modern imaging modalities like magnetic resonance imaging (MRI) and positron emission tomography (PET) in addition to conventionally used computed tomography (CT). This can resolve discrepancies in target delineation in head and neck carcinomas resulting in better local control.Purpose: to compare between 18F-FDG-PET/CT versus CT scan in gross target volume volumes delineation in patients with Head and Neck cancer.Patients and Methods: 30 patients with pathologically confirmed primary HNSCC were enrolled. All patients had planning combined PET/CT in treatment position. All the GTVs (for the primary and nodal disease) were defined from both 18F FDG-PET/CT (GTV- PET) and CT (GTV- CT).A visual interpretation method was used to delineate the margins of the GTV- PET.The CTVs, as well as the PTVs, were created from the GTVs. All volumes had been measured and expressed in cubic centimeters.Results: PET resulted in change of stage for 5 cases, 1 was up staged to metastatic disease was excluded from study treatment and was treated with palliative intent, but toxicity and response data is monitored, 2 was down staged.GTVps delineated using CT scan (C-GTVp) were larger than those delineated using combined PET/CT scan (PET-GTVp) with median volume of 23.45cc compared to 16.67 cc of (C-GTV) and (PET-GTV) respectively however didn’t reach the statistical significance value (P = 0.074).GTVns delineated using CT scan (C-GTVn) were smaller than those delineated using combined PET/CT scan (PET-GTVn) with median volume of 6.85cc compared to 10.67 cc of (C-GTVn) and (PET-GTVn) respectively with statistical significance (P=0.045).Conclusion: the use of PET/CT resulted in change of disease's stage, the primary tumor and nodal GTVns were changed with the implementation of combined PET/CT; that translate into a smaller and statistically significant difference in GTVns of the nodal disease, however, such difference in the volumes was not statistically significant when applied to primary tumor GTVs, CTVs and PTVs..