ESTRO 2020 Abstract Book

S459 ESTRO 2020

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 Purpose or Objective 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 therapy, but also other complications such as other malignancies and chronic obstructive pulmonary disease, and we haven't offered radiotherapy to all cancer patients of active smokers since 2009. Now, we evaluate the outcome of definitive radiation therapy for early stage glottis carcinoma before and after prohibiting smoking. Material and Methods Between 2005 and 2016, 103 patients (male/female =98/5) with early glottis carcinoma (T1N0/T2N0 = 79/24) treated by conventional radiotherapy were reviewed by independent two radiation-oncologists. The median age was 70 year-old (ranging from 46 to 86). The pathology was all squamous cell carcinoma. The prescribed dose was 60 to 70 Gy (median EQD 2 66Gy). The energy of X-ray was 4MV (until 2010) or 6MV (since 2011). Concurrent chemotherapy or molecular target therapy was done in 36 patients. From 2009 we checked that patients cessation of smoking only by medical interviews, and we confirmed it using smokerlyzer® (Bedfont Scientific Ltd. Kent. UK), which detects expiratory carbon monoxide, to monitor their smoking cessation more strictly from 2014 to 2016. The number of patients at diagnosis years was 48 patients from 2005 to 2008, 31 patients from 2009 to 2013, and 24 patients from 2014 to 2016, respectively. We defined each groups, patients from 2005 to 2008 as “freely cigarette”, from 2009 to 2013 as “incomplete cessation”, and from 2014 to 2016 as “complete cessation”. We analyzed local relapse rate as primary endpoint, and over all survival (OS) and disease free survival (DFS) as secondary endpoints. Results The median follow-up period was 53.1 months (range, from 1.9 to 141.0 months). Local control rate at 3 years was 83%, and 3-year local control rates before and after prohibiting smoking were 76% (n=48) and 91%(n=55), respectively. The 2-year and 5-year relapse rate of all patients were 15.6% and 18.8%. The 2-year relapse rate of complete cessation group was 5.3%, and tended to be lower than incomplete cessation group (13.7%) and freely