ESTRO 2024 - Abstract Book

S1364

Clinical - Head & neck

ESTRO 2024

Material/Methods:

Thirty five patients with locally advanced oropharyngeal cancer treated with radiotherapy with intensity modulated radiotherapy technique were studied. Each patient underwent MRI, PET and CT planning scans. Three sets of primary GTVs namely GTV-PET, GTV-CT and GTV-MRI were contoured. In order to know the similarity and harmony between GTVs drawn on different imaging modalities, concordance index (CI) was calculated. The ratio of the common and composite volume is designated as the CI between the chosen modalities. A Pearson product-moment correlation was run to determine the relationship between the three sets of GTV and CI. Paired t-test was run for volumetric comparison between the GTV volumes and CIs.

Results:

The mean GTV-CT, GTV-PET and GTV-MRI volumes were 31.34 ± 32.77 31.27 (range 1.32 – 119.63 cc), 33.87 ± 34.98 33.75 (range 1.51 – 112.87 cc) and 28.12 ± 29.02 25.28 (range 1.12 – 96.22 cc) respectively. A Pearson product moment correlation was run to determine the relationship between GTV-CT and GTV-MRI, GTV-PET and GTV-MRI, and GTV-CT and GTV-PET. There was a very strong, statistically significant positive correlation between the above mentioned 3 sets which was also statistically significant (r = 0.834, p = 0.012; r = 0.821, p = 0.018; and r = 0.867, p = <0.001 respectively). Paired t-tests were run for volumetric comparison between the GTV. There was a significant difference in the GTV CT (M = 30.12cc, SD ± 32.90) and GTV-MRI (M = 26.55cc, SD ± 27.11); t (20) = -2.632, p = 0.031 and in the GTV-PET (M = 33.72cc, SD ± 34.02) and GTV-MRI (M = 27.91cc, SD ± 24.65); t (20) = 2.265, p = 0.039. However, there was no statistically significant difference in the GTV-PET (M = 35.11cc, SD = ± 34.80) and GTV-CT (M = 28.55cc, SD = ±29.03); t (20) = 2.114, p = 0.632. The results suggest that if GTV is delineated on three different modalities, the volumes differed significantly when compared on CT and MRI, and MRI and PET; however volumes did not differ significantly on CT and PET. The mean CI (PET-CT), (CT-MRI) and (PET-MRI), were 0.51 SD ± 0.29 , 0.39 SD ± 0.21, and 0.42 SD ± 0.18 respectively. Paired t-tests were used to compare all the three CIs. There was no significant difference between CI (CT-MRI) vs (PET-CT) , CI (PET-CT) vs (PET-MRI), and between CI (PET-MRI) vs (CT-MRI) , p = 0.801, 0.388 and 0.326 respectively. This signifies the very importance of each individual modality used and emphasizes their combined use for precise delineation.

Conclusion:

There is consistency in delineation of target volumes on all the imaging modalities used. PET and MRI are useful imaging tools in oropharyngeal cancers and should be utilized in combination with CT scan for improved target volume delineation.

Keywords: Concordance index, oropharyngeal cancer