ESTRO 2020 Abstract book

S494 ESTRO 2020

AXB Dw, AXB Dm, and AAA respectively. Minimizing D2% to the mandible may influence ORN rate. Further study is required to determine the relationship between maximum doses, and other potential predictive factors, and ORN. PO-0830 Observation versus Adjuvant Radiotherapy in Early Stage Head and Neck Cancer of Oral Cavity. S.K. Barik 1 , N. Panda 1 , P. C 2 , G. N 2 , P. Moharana 1 , K. Sahni 2 , I. Priyadarsini 1 , S. Mohanty 1 , S. A 2 , R. Meher 1 1 AHRCC, Radiation Oncology, Cuttack, India ; 2 Hcg Regency Oncology Pvt Ltd., Radiation Oncology, Kanpur, India Purpose or Objective The Role of Adjuvant Radiotherapy in Early Stage HNSCC of Oral Cavity is ill-defined especially in depth of invasion ≥ 0.5mm and ≤10 mm The Objective of the study is to do a retrospective analysis in Postoperative Early- stage HNSCC of the oral cavity where observation versus Adjuvant Radiotherapy is to be studied in tumors with a depth of invasion ≥ 0.5 mm and ≤10 mm. The study accessed the Loco Regional Control as Primary Objective and Disease-free Survival, Overall Survival, Toxicity and Quality of Life as Secondary Objectives. Material and Methods The study is a Retrospective analysis of Postoperative Early-stage HNSCC of Oral Cavity treated from November 2016 to September 2019. All patients were restaged according to AJCC staging 8th Edition. Inclusion criteria: T1, T2 tumors, No Neck nodes Involved, DOI ≥ 0.5mm and ≤10 mm,Squamous cell carcinoma histology Exclusion Criteria: N+ disease, close or positive margins, Incomplete dissection, Metastatic disease, Non-Squamous histology. The study compared Observation versus Postoperative Adjuvant Radiotherapy(PORT) in Early Stage HNSCC. The Primary Objective was Loco Regional Control . Secondary Objectives are Disease-free Survival, Overall Survival, Acute, and Chronic Radiation Toxicity and Quality of Life. Patients treated with both conventional and conformal methods were taken up for the study. The data was collected from both electronic and manual sources. Data were analyzed with the help of SPSS v.21. Results 56 patients of Early Stage HNSCC were analyzed for having received Adjuvant PORT(Arm 1) and 48 patients were analyzed for observation(Arm 2). The Median Follow up was 18 months. There was a significant increase in 3 year LRC in Arm receiving Adjuvant RT treatment (85% vs 78%)(p=0.01). Observation arm had a lower 3-year DFS than treatment arm(78% vs 73%)(p=0.34) though the results were not significant. 3-year Overall Survival was equal in both the arms. In patients in the Treatment, arm had 34% Acute Grade II Mucositis,26% Grade III Mucositis. Ryles tube feeding rate was 40%.No hematological toxicity was observed in either of the arms. Quality of Life variables were also compared among the two groups. Immediately after Radiation patients had a lower quality of life scored as compared to Observation arm but the score improved after 3 months post-therapy. A subset analysis was done in patients with the group I DOI ≤0,5MM and ≥0,7 mm, Group II DOI 0.8 mm to ≥10mm. However, no significant difference was found in terms of LRC, DFS, and OS. Conclusion To Conclude Adjuvant Radiotherapy may be advocated in patients with DOI ≥0.5 mm in Early Stage HNSCC. The study had heterogenous subsites of oral cavity HNSCC like Buccal mucosa, Alveolus, Tongue which might have an impact on the results. Also, the treatment arm had few patients treated with conventional cobalt machine which might have impacted the quality of life score. It is desirable to undertake a randomized phase III trial with a particular subsite in a large number of patients to make any further decision.

PO-0829 Osteoradionecrosis of the mandible in head and neck cancer patients treated with VMAT C. Munoz Montplet 1 , J. Marruecos 2 , A. De Pablo 3 , D. Jurado Bruggeman 4 , I. Romera Martínez 4 , A. Onsès 4 , R. Fuentes 2 , J.C. Vilanova 5 1 Institut Català d'Oncologia-Universitat de Girona, Medical Physics and Radiation Protection-Medical Sciences, Girona, Spain ; 2 Institut Català d'Oncologia- Universitat de Girona, Radiation Oncology-Medical Sciences, Girona, Spain ; 3 Institut Català d'Oncologia, Radiation Oncology, Girona, Spain ; 4 Institut Català d'Oncologia, Medical Physics and Radiation Protection, Girona, Spain ; 5 Clínica Girona- Institut de Diagnòstic per la Imatge-Universitat de Girona, Radiology-Medical Sciences, Girona, Spain Purpose or Objective The risk for osteoradionecrosis (ORN) of the mandible is positively related to maximum bone doses above 60 Gy. The aim of this study was to determine the relationship between maximum doses to the mandible and osteoradionecrosis incidence in patients with head and neck (H&N) cancer treated with volumetric modulated arc therapy (VMAT). The study was performed for different algorithms and dose reporting modes. Material and Methods Medical records were reviewed to identify ORN of the mandible and its localization in 106 patients diagnosed with H&N cancer, treated with a prescription dose of 70 Gy using dual-arc VMAT at our institution between October 2013 and May 2015. D2% to the mandible was reported as an alternative to the maximum dose in the spirit of ICRU 83. Calculations were performed with two algorithms implemented in the Eclipse treatment planning system (Varian Medical Systems; Palo Alto, CA, USA), namely the Analytical Anisotropic Algorithm (AAA) and Acuros XB (AXB) for both dose-to-medium (Dm) and dose-to-water (Dw) reporting modes. Other potential predictive factors, such as nicotine and alcohol abuse, age, gender, T stage and chemotherapy type were also studied. Results Grade 1 (asymptomatic) ORN was observed in 3 patients. Fig. 1 shows that mean D2% was between 16.3 % and 18.8 % higher for this group of patients, although the differences were not statistically significant, and that ORN occurred above 77, 69, and 72 Gy for AXB Dw, AXB Dm, and AAA respectively. AXB Dw seemed to have a slightly higher predictive power compared to AXB Dm and AAA, as the percentual difference with the non ORN group of patients was higher and because mandible D2% could be clearly distinguished from the prescription dose. ORN localization correlated with higher dose levels. There was no apparent relationship between ORN incidence and other predictive factors.

Figure 1: Box plot analysis of the relationship between mandible D2% and ORN incidence for AXB Dw, AXB Dm and AAA. Conclusion ORN is relatively uncommon in H&N patients treated with VMAT, although grade 1 disorders are still observed in 3% of the patients for D2% values above 77, 69, and 72 Gy for