ESTRO 2021 Abstract Book

S285

ESTRO 2021

mucositis.

PH-0386 NTCP modeling for late radiation-associated taste impairment in oropharyngeal cancer patients S. Stieb 1 , G.M. Engeseth 2 , L.V. van Dijk 1 , A.S. Mohamed 1 , R. He 1 , I. Perez-Martinez 1 , S. Rock 1 , T.S. Deshpande 1 , A.S. Garden 1 , D.I. Rosenthal 1 , S.J. Frank 1 , G.B. Gunn 1 , C.D. Fuller 1 1 The University of Texas MD Anderson Cancer Center, Department of Radiation Oncology, Houston, TX, USA; 2 Haukeland University Hospital, Department of Oncology and Medical Physics, Bergen, Norway Purpose or Objective To develop a normal tissue complication probability (NTCP) model for taste impairment in oropharyngeal cancer (OPC) patients 5 years after intensity modulated radiotherapy (IMRT). Materials and Methods OPC patients enrolled in a prospective, observational, IRB-approved protocol were included in this study if they fulfilled the following criteria: >18 years, MD Anderson Symptom Inventory (MDASI) taste score available >24 months from IMRT, no dental stent during planning CT and IMRT. MDASI scores from 0–4 were considered as no or mild symptoms and from 5–10 as moderate/severe. D5 – D95 and the mean, minimum and maximum dose for the taste bud bearing tongue mucosa, and the ipsi- and contralateral parotid and submandibular gland were extracted from the planning CT. Binary logistic regression was used to analyze the correlation between clinical parameters, dose volume parameters and moderate/severe taste impairment. Variables with p<0.1 were selected for the multivariate logistic regression analysis with a stepwise forward selection procedure. The model was evaluated using the area under the receiver operating characteristic curve (AUC). Spearman correlation was applied to correlate taste impairment with dry mouth. Results 117 T1–4 OPC patients were included in this analysis. MDASI taste items were queried after a median of 58 months (IQR: 43–68) from RT. The primary tumor was located in the tonsil in 91 cases (78%) and the BOT in 22 cases (19%). Patients received uni- or bilateral RT in 32 (28%) and 84 cases (72%), respectively, with 64.2–72.0 Gy prescribed in 30–40 fractions. 37 patients (32%) received induction, 36 (31%) concurrent chemotherapy and 23 (20%) concurrent targeted therapy. 18 patients (15%) suffered from moderate/severe long-term taste impairment. No dose volume parameter of the tongue mucosa and the salivary glands was significantly associated with moderate/severe taste impairment for all patients. For patients without concurrent chemotherapy the minimum dose, mean dose, D90 and D95 to the ipsilateral parotid gland was significantly associated with moderate/severe taste impairment (all p<0.05). The best predictive parameter of the tongue mucosa was D70, although not significant (p=0.096). The NTCP model included the minimum dose of the ipsilateral parotid gland (OR: 1.140; 95% CI: 1.018 – 1.276) to predict moderate/severe taste impairment with an AUC of 0.67 (95% CI 0.51–0.83). A highly significant correlation was found between taste impairment and dry mouth (p<0.001). Conclusion This is the first NTCP model for late taste impairment. Xerostomia seems to be the predominant factor in the development of moderate/severe symptoms, and sparing of the parotid gland might improve long-term taste impairment. The influence of dose to the taste bud bearing tongue mucosa and of concurrent chemotherapy on taste impairment remains unclear and needs further investigation. PH-0387 Mandible osteoradionecrosis: a dosimetric study L. Humbert-Vidan 1,2 , V. Patel 3 , R.H. Begum 4 , M. McGovern 4 , D. Eaton 4 , A. Kong 5 , I. Petkar 5 , M. Reis Ferreira 5 , M. Lei 5 , A.P. King 2 , T. Guerrero Urbano 5,6 1 Guy's and St Thomas' NHS Foundation Trust, Radiotherapy Physics, London, United Kingdom; 2 King's College London, School of Biomedical Engineering & Imaging Sciences, London, United Kingdom; 3 Guy's and St Thomas' Hospital NHS Foundation Trust, Oral Surgery, London, United Kingdom; 4 Guy's and St Thomas' Hospital NHS Foundation Trust, Radiotherapy Physics, London, United Kingdom; 5 Guy's and St Thomas' Hospital NHS Foundation Trust, Clinical Oncology, London, United Kingdom; 6 King’s College London, Cancer Clinical Academic Group, London, United Kingdom Purpose or Objective Radiation-induced damage to the mandible bone can result in osteoradionecrosis (ORN). Clinical, demographic and dosimetric factors can contribute to the incidence of mandible ORN. There is a lack of recommendations on mandible dosimetric constraints for radiotherapy treatment planning optimisation in head and neck cancer. Existing published studies mostly use the single spatial-point reporting metrics (e.g. Dmax) rather than the dose-volume reporting (e.g. D2%) recommended in the ICRU Report 83, which is more relevant to the IMRT era. This work aims to provide a comprehensive analysis of dosimetric associations with mandible ORN incidence. Materials and Methods A total of 81 HNC patients with ORN and 81 HNC control cases were selected from the local clinical HNC database. Inclusion criteria required either a confirmed clinical, radiographic or histopathological diagnosis of ORN following head and neck RT. Only cases with a minimum follow-up time of 3 years were included in the control group. DVH-based dosimetric data was analysed retrospectively. The Mann-Whitney U non-parametric statistical test with a significance level of 0.05 was used to compare the two groups at dose-volume levels between V30Gy and V70Gy and at maximum (Dmax and D2%), minimum (Dmin and D98%) and median dose levels. Mandible volumes were also compared between the two groups. Results Dmin (p=0.000), D98% (p=0.000), Dmax (p=0.003), D2% (p=0.000), V60Gy (p=0.007), V65Gy (p=0.002) and V70Gy (p=0.041) were statistically significantly different between the two groups. Mandible volumes were significantly larger in the ORN group compared to the control group with median values of 61.8 cc (range 29- 111 cc) and 56.4 cc (range 23-90 cc), respectively (p=0.021). A difference of 3 Gy was observed between