Improving the accuracy of target volume delineation by combined use of computed tomography, magnetic resonance imaging and positron emission tomography in head and neck carcinomas.

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. We hereby report the comparison of Gross Tumor Volumes (GTVs) (primary) drawn using PET, CT and MRI and their concordance indices.

Methods And Material: Twenty five patients with head and neck cancer were taken into this study. MRI, PET and CT planning scans were done as per standard guidelines. Three sets of primary GTVs namely GTV- PET, GTV-CT and GTV-MRI were contoured on fused images. All the three volumes and concordances among the volumes were analyzed.

Result: The mean GTV-CT, GTV-PET and GTV-MRI volumes were 29.65 cc ± 31.27, 32.05 cc ± 33.75 and 24.85 cc ± 25.28 respectively. There was a significant difference in the GTV-MRI & GTV-CT volumes (P = 0.023) and GTV-PET & GTV-MRI volumes (P = 0.049). However, there was no significant difference in the GTV-PET & GTV-CT volume (P = 0.468). The mean CI (PET-MRI), CI (CT-MRI) and CI (PET-CT) was 0.42, 0.46 and 0.47 respectively, which depicts a moderate concordance.

Conclusion: PET and MRI are useful imaging tools in head and neck malignancies and should be used in conjunction with CT scan for improved target volume delineation.