ESTRO 2024 - Abstract Book

S1251

Clinical - Head & neck

ESTRO 2024

In the statistical analysis of the relationship between masseter dose and trismus, we pooled the data from the two cohorts. Patients with trismus were assigned the binary endpoint of 1, and patients without trismus were assigned 0. The role of bilateral masseter mean absorbed dose was investigated in univariable logistic regression using maximum likelihood estimation. The dose- response parameters {γ 50 , D 50 } were estimated, and the statistical significance of the model fit was calculated using the likelihood ratio test. The confidence intervals (CIs) for the estimated parameters were calculated using the profile-likelihood method. We used bootstrapping to estimate the CI of the resulting dose-response relationship using 5000 bootstrap samples. P- values≤0.05 were considered statistically significant.

Results:

After applying the exclusion criteria, the number of patients available for analysis was 121/224 in cohort 1 and 124/239 in cohort 2, Figure 1. In cohort 1, the average age (± 1 S.D.) was 59±11 years and 72% of the patients were men. The corresponding numbers in cohort 2 were 64±8 years and 77%. The average masseter mean dose was 35.2±8.3 Gy in cohort 1 and 20.2±8.7 Gy in cohort 2. Within 12 months after completed RT, 74/121 (61%) of patients in cohort 1 had experienced trismus compared to 11/124 (9%) of patients in cohort 2. The dose- response parameters and their CIs were estimated as γ 50 =1.31 (95% CI: 1.00-1.68) and D 50 =34.0 Gy (95% CI: 32.0-36.5). The model fit was found to be statistically significant, p<10-11. The resulting dose-response curve is shown in Figure 2 together with its 95% CI. According to the estimated dose-response relationship, a bilateral masseter mean absorbed dose below <20 Gy predicts the risk of radiation-induced trismus to be <10%.

Figure 1. Consort diagram. Patients reported in the “Surgery” category were excluded due to having undergone “Surgery likely to affect trismus development”. Abbreviation: MIO = maximal interincisal opening.