Introduction: Head and neck cancers are the seventh most cancer with 30% from Indian population, of which 16% are oral cavity cancers .70% patients present with locally advanced unresectable disease with substantial risk of cervical node metastasis for which CTRT is the definitive treatment. Detecting metastatic cervical nodes with conventional imaging techniques has limitations which are solved by noninvasive 18F FDG PET CT Scan. Using PETCT scan to delineate the GTV of primary tumor and nodal is compared with planning CECT in this study.

Objectives:  To define radiation planning volumes (Gross tumor volume for tumor and lymph nodes) with 18F FDG PETCT compared to CECT scan.

Material and Methods: 25 biopsy proven patients with oral cavity tumors were assessed prospectively for a study period of 2 years from 2020 to 2022 in a single tertiary cancer institute. All the patients underwent PETCT scan and was registered to planning CECT scan where the volumes are compared in cc.

Statistical Analysis:  paired T test with all correlations done using chi square test with p<0.05 considered statistically significant.

Results: Of all 25 patients, 88% males and 12 % female patients with most fall below 51 years 81%(15) and 10%(10) above 51 years. Out of all subsites Buccal mucosa 52%, Oral tongue 32% , retro molar trigone 8%,alveolus 8% and floor of mouth 4%. Most patients have squamous cell carcinoma as histology. On assessing GTV volumes of primary tumor and nodes in planning CECT scan and fused 18F-FDG PET CT scan the mean volume GTV P(primary) of CECT scan is 61.07 cm3 with standard deviation of 55.704cm3 and on PETCT mean is 47.80 cm3 with standard deviation of 29.783 cm3, p value <0.037 with mean difference of 13.26cm3. The mean of GTV N (nodal) in CECT is 20.41 cm3 with standard deviation of 18.719cm3 compared to PET mean of 16.29 with standard deviation of 16.678cm3, p value <0.007 with the mean difference of 4.11cm3.

Conclusion: On reviewing the above results, using FDG PET CT scan in planning CECT scan may decrease the GTV p and GTV n, which further may decrease the planning volume.

Keywords: Oral cavity cancers, Radiotherapy, GTV delineation, PETCT GTV delineation, CECT GTV delineation, Target Volumes, PETCT Vs CECT GTV.

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Dr Prathyusha Nanuvala

Associate professor, Department of Radiation Oncology, Osmania medical college, Hyderabad, India