ESTRO 2020 Abstract book

S504 ESTRO 2020

Adjuvant radiation in oral cavity malignancies has seen major progress in treatment delivery with the use of Intensity Modulated Radiation therapy (IMRT) which provides better organ sparing without compromising on tumor coverage. Even though xerostomia has been significantly reduced with IMRT, it still has a significant impact on the patient's long term quality of life. The focus so far has primarily been on parotid gland sparing to prevent xerostomia while other salivary structures, especially the contralateral submandibular gland has been a relatively ignored entity. Our study aims to define the dose constraints needed to be achieved to reduce xerostomia further. Material and Methods From June 2014 to Sept 2018, a total of 48 patients with histopathologically proven oral cavity malignancies who underwent surgery and had indications for adjuvant radiation therapy were retrospectively analyzed for this study. These patients were taken from the medical records of the Radiation Oncology department of our hospital. The patients were assessed as per the follow up protocol at 6 months and 12 months following completion of radiotherapy. They were assessed for xerostomia as per CTCAE 4.0 grading system. All these patients were planned with only parotid sparing IMRT, achieving a contralateral parotid mean of < 26 Gy strictly.The dosimetric parameters were evaluated from the DVH of patients and parameters involving the parotid glands (mean, D20cc both glands, D50% contralateral), submandibular gland (contralateral mean dose) and oral cavity minus PTV mean doses were assessed. The association between these and xerostomia grades were analyzed using analysis of variance and multivariable logistic regression analysis. Results With a median follow up of 12 months, there were 47 patients who developed some grade of xerostomia. Majority of the patients had malignancy of buccal mucosa as the primary with male preponderance. None of the patients had baseline xerostomia or mucosal abnormalities. The Grade I, II and III xerostomia toxicities at 6 months were seen in 33.33%, 45.83% and 18.75% and at 12 months was 41.86%, 44.18% and 13.95% respectively. There were 6 patients who had an enhancement in toxicity grade at second follow up. Significance was seen in toxicity association with the contralateral submandibular gland dose and a dose more than 14.78Gy (p=0.007) was associated with Grade III toxicity. Similarly, oral cavity minus PTV dose of more than 32.82Gy (p <0.001) was associated with grade III xerostomia. There was trend towards significance with D50% dose of parotid glands, however this was not statistically significant. Conclusion Submandibular gland contouring and strict dose constraints are an often ignored aspect in treatment planning for oral cavity malignancies. With the defined dose constraints in our study, we can aim at reducing xerostomia even further, thereby improving upon the therapeutic ratio. Further prospective studies and a larger sample size are required to validate our findings. PO-0853 The effect of the smoking cessation for radiation therapy of glottis carcinoma with monitoring CO S. Tatekawa 1 , S. Shimamoto 2 , T. Nishi 2 , M. Tani 2 , T. Ohsima 2 , S. Onosaka 2 , Y. Komeya 2 , Y. Yamashita 2 , K. Tamari 1 , K. Ogawa 1 1 Osaka University Graduate School of Medicine, Department of Radiation Oncology, Suita-city, Japan ; 2 Osaka General Medical Center, Radiation and oncology, Osaka, Japan Purpose or Objective Cigarette smoking during radiation therapy is associated with unfavorable outcome in various cancers. In addition, smokers not only have complications during radiation

Nice, France ; 5 Centre Antoine Lacassagne, biostatistics, Nice, France Purpose or Objective Cutaneous squamous cell carcinoma (CSCC) is one of the most common malignant tumors worldwide. There is conflicting evidence regarding the indications for and benefits of adjuvant radiation therapy (ART) for head and neck cutaneous squamous cell carcinoma (HNCSCC). New evidence-based risk stratification system as Brigham and Women’s tumor classification (BWH) may optimize identification of patients who benefit from ART compare to ancient classification. Our objective was to compare outcomes between patients who underwent surgery alone with those who received ART to identify ART indications. Material and Methods All patients undergoing primary surgery with or without adjuvant radiation therapy with curative intent for HNCSCC treated from April 2007 to December 2018 in our center were included. We made a retrospective monocentric study and collected major patient data and tumor characteristics (including American Joint Committee on Cancer, 8th edition (AJCC-8) staging system and BWH classification). Results A total of 290 HNCSCCs were included in this study, of which 241 (83.1%) were men with the mean age of 78.3 (36-100) years. Twenty-one (7.2%) patients were immunosuppressed, 41 (14.2%) patients were nodes- positive (N+) , 105 (36.2%) patients were treated for recurrent disease, 28 (9.65%) patients were margin- positive and 82 (28.3%) patients received post-operative ART. According to BWH classification, 88 (30.3%) patients were T1, 76 (26.2%) were T2a, 100 (37.9%) were T2b and 16 (5.5%) were T3. The 3-year Kaplan-Meier estimates were 50.2 %for Disease- Free Survival (DFS) and 76.0%for Overall Survival (OS). Median DFS were 61.7 (52.5-70.9) months for T1 patients, 64.7 (49.5-80.8) months for T2a patients, 36.9 (26.4- 47.3) months for T2b patients and 16.2 (7.5-25.0) months for T3 patients. Median OS were 94.4 (86.3-102.4) months for T1 patients, 90.9 (80.3-101.4) months for T2a patients, 48.5 (41.5- 55.6) months for T2b patients and 36.1 (28.2-43.9) months for T3 patients. For T2a patients, median DFS was 42.0 (30.6-53.4) months for irradiated patients and 28.2 (22.3-34.1) months for non-irradiated patients and. There was no association between adjuvant radiation therapy and DFS for T2a and T1 patients (respectively p=0.217 and p=0.295). For T2b patients, median DFS was 58.8 (45.2-72.6) months for irradiated patients and 14.3 (9.8-18.8) months for non- irradiated patients. There was a clear association between adjuvant radiation therapy and DFS for T2b and T3 patients (p<0.0001) despite an initial worse presentation for irradiated patients. Conclusion According to our results, ART after surgery increase survival for T2b and T3 WBH patients. New RT guidelines for HNCSCC should include BWH classification for a better selection for adjuvant treatment. PO-0852 Can we ignore Submandibular gland constraints for Xerostomia prevention in Parotid sparing IMRT? K. George 1 , K. Talapatra 1 , V. Mhatre 1 , P. Chadha 1 , M.S. Deshpande 2 , R. Mistry 2 1 Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute, Radiation Oncology Department, Mumbai, India ; 2 Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute, Surgical Oncology Department, Mumbai, India

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