ESTRO 2020 Abstract book

S476 ESTRO 2020

OARs manually segmented on planning CT scans were: bilateral parotid and submandibular glands, superior and middle pharyngeal constrictor muscles, supraglottic larynx and oral cavity. Contours were propagated to daily MVCTs with a specifically trained and validated open source DIR algorithm (Elastix). Daily dose was calculated with an in- house ray-tracing algorithm (CheckTomo), and accumulated to estimate delivered DVH. Planned dose was recalculated with CheckTomo for direct comparison. Toxicity data for the following endpoints were binarised for analysis: CTCAEv4.03 – xerostomia, salivary duct inflammation and dysphagia, EORTC H&N35 - dry mouth (Q41), sticky saliva (Q42), taste disturbance (Q44), LENT/SOM – xerostomia subjective, xerostomia management. Forward stepwise variable selection by likelihood ratio fed statistically significant baseline and mean OAR D P variables (from univariate analysis) into logistic regression based multivariate NTCP models, which were internally validated/calibrated with 1000-fold bootstrapping and10-fold cross-validation. The process was repeated with mean OAR D A metrics, and D P and D A - based model performance was compared with Nagelkerke R 2 , -2 log-likelihood, discrimination slope (DS), and ROC curve AUC statistics. Results Baseline/12 month toxicity prevalence is shown in Table 1. CTCAE v4.03 Xer. Gr2+ SDI Gr2+ Dysph. Gr2+ Baseline 7 (3.5%) 5 (2.5%) 11 (5.6%) 12m 75 (37.9%) 88 (44.4%) 39 (19.7%) EORTC H&N 35 Q41 Gr3+ Q42 Gr3+ Q44 Gr3+ Baseline 16 (8.1%) 12 (6.1%) 16 (8.1%) 12m 95 (48%) 62 (31.3%) 74 (37.4%) LENT/SOM Subj. Xer. Man. Xer. Baseline 16 (8.1%) 1 (0.5%) 12m 94 (47.5%) 82 (41.4%) Table1: Proportions of patients reporting threshold toxicity at baseline and 12 months On average, D A was higher to all OARs (range 0.44 – 1.56Gy). Table 2 shows summary D P and D A -based model performance data, and ROC curve AUC results. These data, as well as model DS results are shown in Figure 1.

Conclusion All models were statistically significant predictors of toxicity. Interestingly, respective D A models had superior Nagelkerke R 2 statistics for 6/8 endpoints, 6/8 ROC curve AUCs, and 8/8 discrimination slopes, but differences were minimal. This may be of interest for future NTCP model development, but supports the notion that dose deltas are clinically insignificant in most patients, and careful case selection is required for optimised ART. PO-0794 Induction chemotherapy followed by moderately accelerated IMRT in head and neck cancer patients A. Re 1 , S. Cilla 2 , M. Ferro 1 , A. Ianiro 2 , G. Macchia 1 , V. Picardi 1 , M. Boccardi 1 , S. Cammelli 3 , C. Romano 1 , D. D'Addario 4 , M. Buwenge 3 , S. Mignogna 5 , M. Ferro 1 , V. Valentini 6 , G. Sallustio 7 , A.G. Morganti 3 , F. Deodato 1 1 Fondazione "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, UO di Radioterapia, Campobasso, Italy ; 2 Fondazione "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, UO di Fisica Sanitaria, Campobasso, Italy ; 3 Dipartimento di Medicina Specialistica Diagnostica e Sperimentale- DIMES- Azienda Ospedaliera-Universitaria S.Orsola-Malpighi, U.O. di Radioterapia, Bologna, Italy ; 4 PO ‘S. Timoteo’, UO di Oncologia Medica, Termoli, Italy ; 5 Fondazione "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, UO di Oncologia Medica, Campobasso, Italy ; 6 Fondazione Policlinico Universitario A. Gemelli- IRCCS, UOC di Radioterapia- Dipartimento di Scienze Radiologiche- Radioterapiche ed Ematologiche, Roma, Italy ; 7 Fondazione "Giovanni Paolo II"- Università Cattolica del Sacro Cuore, UO di Radiologia, Campobasso, Italy Purpose or Objective To assess the feasibility and toxicity profile of treatment with induction chemotherapy (iCT) followed by moderately accelerated intensity-modulated radiation therapy (IMRT/VMAT) and weekly cisplatin in patients (pts) with locally advanced or recurrent head and neck cancer (LAHNC). Material and Methods Two or three cycles of docetaxel, cisplatin and 5- fluorouracil (DCF) or with cisplatin and 5-fluorouracil (CF) were prescribed. Thereafter, radiotherapy was delivered