ESTRO 38 Abstract book

S367 ESTRO 38

comparable with literature on conventional schedules for small tumors and survival was good in this population with 60% of advanced stage III-IVa disease. Strategies to mitigate severe toxicity risks are under investigation to improve the tolerability of the SBRT boost.

the end of the treatment, 1/60 patients in the PDRN group vs. 4/60 patients in the control group had G1 grade of skin toxicity (p=0.047). No differences were seen regarding other variables examined. Conclusion PDRN based cream improves the acute skin toxicity profile of head and neck cancer patients undergoing CTRT. In these patients, the maximum skin toxicity grade is lower and the complete skin healing is faster. We need more patients and a longer follow up to assess late toxicity as fibrosis. PO-0714 Toxicity profile of a SBRT boost as first-line treatment in oropharyngeal cancer patients W. Heemsbergen 1 , S. Baker 1 , S. Petit 1 , J. Nuyttens 1 , G. Verduijn 1 1 Erasmus MC Cancer Institute, Radiation Oncology, Rotterdam, The Netherlands Purpose or Objective To date, stereotactic body radiotherapy (SBRT) for head and neck cancer has been used primarily for re-irradiation of recurrent malignancies, despite the potential advantages in the setting of newly diagnosed disease and a growing interest internationally. There is sparse literature on long-term toxicity patterns in large patient series in the setting of a first-line treatment. In the current study we determined the late Grade ≥3 toxicity rates of a SBRT boost as primary treatment in the largest patient series to date. Material and Methods We performed a retrospective cohort study in 195 consecutive oropharyngeal squamous cell carcinoma patients collected from a prospective planning database. Eligible patients had T1-small T3 disease for which they were treated between 2009-2016 with a SBRT boost (3 x 5.5 Gy) to the primary tumor after accelerated 46 Gy IMRT to the primary tumor and neck, plus additional neck dissection in case of N positive disease ( Table) . The boost was delivered with a frameless robotic radiosurgery system. The GTV-CTV margin was 1 cm and the CTV-PTV margin was 5 mm for the IMRT phase and 3 mm for the boost. Main OAR dose constraints for the total plan (EQD2) were: spinal cord Dmax < 50 Gy and brain stem Dmax <60 Gy (both hard planning constraints), parotid glands Dmean <26 Gy, submandibular glands Dmean <39 Gy, oral cavity Dmean <50 Gy, swallowing structures Dmean <55 Gy (where achievable). We determined Grade ≥ 3 toxicity rates(G≥3) as well as locoregional control (LRC), disease- specific survival (DSS), and overall survival (OS). Prognostic factors were assessed in Cox regression models. Sufficient follow-up (disease-free survival > 3 months post-RT) for late toxicity assessment was available for 182 patients. Results Median follow-up was 4.3 years. Treatment compliance (100%) was high. Rates of cumulative 5-year (5Y) late G≥3, LCR, DSS, and OS were 26%, 84%, 85%, and 67%, respectively. The most frequently observed G≥3 toxicities were mucosal ulceration or soft tissue necrosis (n=29, 5Y 17%), dysphagia or weight loss (n=15, 5Y 10%) and osteoradionecrosis (ORN) (n=11, 5Y 9%). At multivariable analysis, current smoker status was associated with increased G≥3 risks (HR=3.3, p<0.01), and pre-RT tooth extraction was associated with increased ORN risk (HR=6.5, p<0.01) Figure . Median interval extraction-start RT was 18 days and was not associated with ORN (n=63,HR=1.9,p=0.4). Charlson Comorbidity Index ≥2 was associated with increased risks of dysphagia/weight loss (HR=6.6, p=0.01). These risk factors appeared to be more pronounced than reported in literature for conventional

PO-0715 Nutritional intervention in head and neck cancer patients undergoing radiotherapy L. Gutierrez Bayard 1 , M.D.C. Salas Buzón 1 , S. Garduño Sánchez 1 , M.J. Macias Lozano 1 , R. Rodríguez Sánchez 1 , S. Sayago Gil 1 , V. Díaz Díaz 1 , E. González Calvo 1 , I. Villanego Beltrán 1 , A. Ruiz Herrero 1 , M. Lorente Sánchez 1 , J. Jaén Olasolo 1 1 Hospital Universitario Puerta del Mar, Radiation Oncology, Cadiz, Spain Purpose or Objective To evaluate the benefit of motivational interviewing in addition to nutritional counseling in head and neck cancer (HNC) patients undergoing radiotherapy (RT)(+/- systemic treatment), to improve patients' nutritional behaviours. Material and Methods Sixty-one intervention patients received motivational interviewing and cognitive behavioural therapy compared

treatment. Conclusion

Grade ≥3 toxicity profiles showed relatively high rates of soft tissue necrosis and osteonecrosis. LCR rates were