ESTRO 2024 - Abstract Book

S2229

Clinical - Upper GI

ESTRO 2024

Results:

In the discovery cohort (median follow-up 17 months, range 1.4-47), 12 patients experienced LF. The GTV size (p=0.007, risk factor for LF, Hazard Ratio [HR] 1.04 for one cc increase in GTV size) and GTV70 (p=0.2, risk factor, HR= 3.73 for GTV70=yes) were selected at UVA and included in MVA. GTV size was dichotomized as below/above 25cc (selected from Youden Index on the ROC curve):HR=9.3. Dichotomized GTV size and GTV70 were used to build a 3 level Geometric Score for the prediction of the risk of LF: -Low- Risk (LR) if “GTV<25cc AND GTV70=no”; -Intermediate Risk (IR) if "GTV>25cc OR GTV70=yes";-High- Risk (HiR) if “GTV>25cc AND GTV70=yes”.The model classified 10 patients in LR, 21 patients in IR, and 19 in HiR patients classes. Patients categorized at HiR had a significantly higher probability of LF: HR=6.9 (95%CI 1.5-32.9) compared to LR, and HR=13.2 (95%CI 3.6-48.4) compared to IR. 10/12 LFs are in the HiR group. The actuarial probability of LF was 62% in the HiR group vs 7% in the others. The mean time to LF is 38, 35, and 23 months for the LR, IR, and HiR classes, respectively (Figure2A). Applying this model to the validation cohort (median follow-up 30 months, range 8-63), patients were subdivided as follows: 8 in LR, 60 in IR, and 14 in HiR risk class. The actuarial rate of LF was not significantly different among the three classes (LogRank p=0.082), while it was significantly different when considering the HiR vs IR (p=0.037). The population size for the different risk classes could explain this statistical effect. In particular, we had only 8 patients in the LR and 3 LFs, making an LR rate of ∼ 40%+/-40% (95% confidence level), which makes findings for the LR class not statistically significant. For this reason, we merged the LR and IR classes and created a two-class Geometric Score. Low Intermediate risk class (L-IR) owns at least one of the favorable features (GTV<25 cc or GVT70=no), and HiR with no favorable features. With these two classes' geometric score, we obtain HR=2.56 (95%CI 1-6.57) and LogRank p=0.042. The LF actuarial rate at 20 months was 31% vs 72% in the L-IR vs HiR risk.The mean time to LF is 32 vs 20 months, respectively (Figure 2B).