ESTRO 36 Abstract Book

S588 ESTRO 36 2017 _______________________________________________________________________________________________

(Rs>0.75) were not included in the multivariate analysis. A two-variable model was suggested as the optimal order by bootstrap method. The optimal model (Rs=0.452, p<0.001) includes V45 of the cervical esophagus (OR=1.016) and Dmean of the cricopharyngeal muscle (OR=1.057). The model AUC (Fig1a) was 0.82 (95% CI 0.69- 0.95). The comparison of the predicted incidence of acute radiation-related toxcity and the actuarial incidence in the population is shown in Figure 1b.

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EP-1078 Transient xerostomia in head and neck cancers with significant parotid inclusion in target volume A. Datta 1 , A. Mukherji 1 , E. Thiraviyam 1 1 Jawaharlal institute of post graduate medical education and research, radiation oncology, Puducherry, India Purpose or Objective To assess xerostomia patterns in patients requiring significant parotid inclusion in target volumes for treatment of locally advanced head and neck cancers. Material and Methods 30 patients (male = 20, female = 10) with head and neck cancers (oral cavity = 6, oropharynx = 8, nasopharynx = 3, larynx = 7) of AJCC stage II = 4, III = 12, and IV = 14 who were treated with radical chemo radiation from August 2013 – September 2015 and received significant parotid dose (more than 22 Gy Dmean) were analyzed retrospectively at 3, 6 and 12 months post completion of treatment. They received an external radiotherapy dose of 69.34 Gy EQD2 (to HR-CTV, mean HI – 0.13, mean CI – 0.99) using SIB-IMRT by VMAT technique. Their xerostomia patterns were recorded based on subjective complaints (Grade 1 = slight dryness, Grade 2 = moderate dryness, Grade 3 = complete dryness, Grade 4 = fibrosis). Results 1 patient died during treatment due to aspiration and 1 patient developed a second primary in lung at 10 months. The mean of Dmean to right parotid was 43.95 Gy (23- 51.2) to a mean volume of 16.71 cc (9-30.2) while for the left parotid it was 43.6 Gy (23.1-58.2) to a mean volume of 16.9 cc (7.7-26.3). The mean spared right parotid (outside PTV) Dmean was 23.1 Gy (30.2-69.2% of whole parotid volume, mean volume 42.5%) while for the left parotid it was 26.3 Gy (22-65% of whole parotid volume, mean volume 48.7%). At 3 months of completion of treatment Grade 2 and 3 xerostomia were seen in 2 (6.9%) and 27 (93.1%) patients respectively. At 6 months Grade 2 and 3 xerostomia were seen in 12 (41.3%) and 17 (58.7%) patients respectively. While at 12 months Grade 1, 2 and 3 xerostomia were seen in 7 (24.1%), 16 (55.2%) and 6 (20.7%) respectively. 1 patient had a stable residual disease. Conclusion Significant parotid inclusion in target volumes for locally advanced cases had a reversible loss of parotid function at 12 months of completion of treatment. However, loss of function was irreversible when the Dmean was greater than or equal to 50 Gy. EP-1079 Carotid blowout syndrome after reirradiation with particle therapy in the head and neck region J.E. Dale 1 , S. Molinelli 2 , E. Ciurlia 2 , O. Dahl 1,3 , P. Fossati 2,4 1 Haukeland University Hospital, Department of oncology, Bergen, Norway 2 CNAO Foundation, Pavia, Italy 3 University of Bergen, Department of clinical science, Bergen, Norway 4 European Institute of Oncology IEO, Milano, Italy Purpose or Objective Carotid blowout syndrome (CBS) is a serious complication to treatment of neoplasms in the head and neck (H&N) region. Surgery, infection, necrosis and tumor properties are the most significant risk factors, but the rate of CBS is also affected by properties of radiotherapy (RT). Rates seem to increase in hypofractionated or accelerated hyperfractionated regimens. We here investigate the cumulative doses received by the carotid artery (CA) and CBS-rate in a cohort of patients reirradiated with particle therapy in the H&N region. Material and Methods

Conclusion We propose a 2-variable predictive NTCP model including both cervical esophagus and cricopharyngeal muscle dosimetric parameters with a good prediction performance for acute radiation-related toxicity in H&N