875 / 1096
S859
ESTRO 36
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assessed according to CTCAE v4.0 at baseline and weekly
during RT. Four endpoints were considered: mean grade
(G) ≥1.5 and G≥3 oral mucositis (OM), G3 dysphagia and
G≥2 salivary dysfunction (SD). The selected OARs were:
oral cavity (OC) and parotid glands (PG) considered as a
single organ for OM and SD; OC, pharyngeal constrictor
muscles (PCM), supraglottic and glottic larynx (GL) for
dysphagia. DVHs were reduced to Equivalent Uniform Dose
(EUD): for each OAR the best volume parameter n was
determined through numerical optimization. When this
procedure did not converge, we chose to evaluate DVH
cutpoint through t-test. EUD was inserted into a
multivariable logistic (ML) model together with
clinical/treatment features; variables selection was
guided by LASSO. Goodness of fit was evaluated with
Hosmer-Lemeshow test and calibration plot.
Results
Data were collected for 132 pts. MeanG≥1.5 and G≥3 OM
were reported in 40 pts (30%), G3 dysphagia in 50 (38%)
and G≥2 SD in 90 (68%). ML models (figures 1-2) consisted
in: a single variable for meanG≥1.5 OM, i.e. OC EUD with
n=1 (mean dose) (OR=1.07); 3 variables for G≥3 OM
including OC EUD with n=0.05 (OR=1.02), PG EUD with n=1
(OR=1.06), BMI≥30 (OR=3.8, obese pts); 3 variables for
dysphagia including PCM V50Gy (OR=1.02), GL and OC EUD
with n=0.35 and 0.15 respectively (OR=1.02 and 1.04); 4
variables for SD including PG D98% (OR=1.04), OC EUD with
n=0.05 (OR=1.11), age (OR=1.08, 5-year intervals), smoke
(OR=1.37, yes vs no). Calibration was good in all cases.
Conclusion
OC resulted to be a parallel organ for mean G≥1.5 OM,
while severe OM was associated to a synergic effect
between PG mean dose and high doses received by small
OC volumes, with BMI acting as a dose-modifying factor.
On the other hand, OC resulted as a fairly serial organ for
G≥2 SD; this could be due to the inclusion of minor salivary
glands in OC contour, that the target often overlaps. Older
age and smoking history were also associated to a SD
increased risk. We did not find a strictly significant
association between G3 dysphagia and dosimetric
features, but the step trend resulting from our model
calibration suggests that the ML model may not describe
well the dose-response relationship in this case, with a
step function possibly being more suitable. Validation of
these models in a larger pts cohort is ongoing.