ESTRO 2020 Abstract book

S560 ESTRO 2020

clinician-assessed visual rating scales, and self-reporting questionnaires. Conclusion The use of the film-forming silicone gel appears to have a positive effect toward reducing radiation dermatitis compared to that of a moisturizing cream. The results of this study will support the feasibility of conducting a larger randomized control trial. PO-0965 Cardiac dosimetry with or without ABC in left breast cancer irradiation: Single institute experience V. Pareek 1 , R. Bhalavat 2 , M. Chandra 2 , P. Bauskar 2 , N. Kumar 2 , E. Kotilingala 2 , P.L. Iyer 2 1 National Cancer Institute- AIIMS, Radiation Oncology, New Delhi, India ; 2 Jupiter Lifelines Hospital, Radiation Oncology, Thane, India Purpose or Objective Cardiac toxicity is a major concern for left breast tangential field irradiation. The left ventricle and left anterior descending (LAD) artery are suggested to be radiosensitive and radiation to these structures leads to late cardiotoxicity. Moderate deep inspiration breath hold (mDIBH) during radiation treatment delivery helps in reducing the cardiac dose. This study compares dosimetric parameters of heart with and without active breath coordinator (ABC) mDIBH during tangential field breast cancer radiation. Material and Methods In our dosimetric comparative study, Thirty consecutive patients with left-sided breast cancer who underwent breast-conserving surgery and adjuvant tangential field and radiotherapy with ABC mDIBH between July 2018 and September 2019 in our center were analyzed in this study. The ABC device was used for respiratory control and patients who could hold their breath for 20–30 s were considered for radiation with ABC mDIBH. Simulation scans of both free breathing (FB) and ABC mDIBH were done. Tangent field treatment plans with a dose prescription of 40 Gy/15 Fr were generated for each patient, in both scans. Target coverage, dose to the heart, LAD, and the left lung were documented with dose-volume histograms. Results Statistical Package for the Social Sciences, version 20 software, was used for analysis and the level of significance was set at P < 0.05. Mean heart dose was 308.5cGy with FB and 159cGy with ABC ( P < 0.0001). Mean dose to the LAD was reduced by 53.81% (1320.64 cGy vs. 606.56 cGy, P < 0.001). Target coverage was equal in both the plans. Conclusion We report that the use of ABC mDIBH technique resulted in a significant reduction in cardiac dose and hence can be considered as a promising tool for cardiac sparing. PO-0966 Partial breast irradiation at the 1.5T MR- Linac: treatment time and electron stream effect C. De Colle 1 , M. Nachbar 2 , D. Mönnich 2,3 , S. Boeke 1 , C. Gani 1 , N. Weidner 1 , V. Heinrich 1 , J. Winter 2 , S. Tsitsekidis 2 , O. Dohm 2 , D. Thorwarth 2 , D. Zips 1,3 1 Department of Radiation Oncology. University Hospital and Medical Faculty. Eberhard Karls University Tübingen. Tübingen. Germany, Radiooncology, Tübingen, Germany ; 2 Section for Biomedical Physics. Department of Radiation Oncology. University Hospital and Medical Faculty. Eberhard Karls University Tübingen- Tübingen. Germany, Radiooncology, Tübingen, Germany ; 3 German Cancer Consortium DKTK- partner site Tübingen and German Cancer Research Center DKFZ- Heidelberg. Germany, Radiooncology, Tübingen, Germany Purpose or Objective Low-risk breast cancer patients can be effectively treated with adjuvant external beam partial breast irradiation (PBI). The newly clinically introduced magnetic resonance

V12Gy, V16Gy and V20Gy). We assessed correlation between dosimetry plans according to periclavicular radiation, and then we evaluated factors that influence D_mean that are lung volume (cm 3 ), beam energy (6MV, 18MV, 6+18MV), chest wall separation(cm), distance to the lung apex(cm), depth of periclavicular volume (cm) and size of periclavicular field(cm) Results Mean D_mean, V4(Gy), V8, V10, V12, V16 and V20 for plans with tangential and periclavicular fields were 10Gy, 43%, 34%, 31%, 29%, 25% and 23% respectively versus 6Gy, 27%, 21%,19%, 18%, 16% and 14% respectively for plans with tangential fields without periclavicular fields. The contribution of periclavicular fields was statistically significant in all cases (p< 0.0001). A significant correlation was found between D_mean and length of periclavicular field (p=0.033), distance to the lung apex (p=0.001) and chest wall separation (0.001). There was no correlation with width of periclavicular field (p=0.263), lung volume (p=0.129), depth of periclavicular field (0.093), and beam energy (p=0.443). Conclusion Periclavicular field increased significantly all ipsilateral lung dosimetric parameters (p<0.001). It contributed up to 40% of D-mean (about third of the dose). Factors affecting D-mean were length of periclavicular field, distance to the lung apex and chest wall separation. Therefore, an accurate contouring of level 3 and 4 areas according to ESTRO guidelines is mandatory to ovoid large fields and exceeded dose to the lung. PO-0964 Reducing radiation dermatitis using a film- forming silicone gel: a pilot randomized controlled trial K. Sung 1 , S. Ahn 1 , H.J. Kim 1 , Y.E. Choi 1 , Y.K. Lee 1 , J.S. Kim 2 , S.K. Lee 2 , J. Roh 2 1 Gachon University Gil Medical Center, Radiation Oncology, Namdong-gu- Incheon, Korea Republic of ; 2 Gachon University Gil Medical Center, Dermatology, Namdong-gu- Incheon, Korea Republic of Purpose or Objective Various topical agents have been used to manage radiation dermatitis during radiation therapy. No topical agent has proven to be better than any other. This work aims to validate the efficacy of a film-forming silicone gel (StrataXRT ® ) for patients receiving whole breast radiotherapy. Material and Methods A single institutional, open-label, randomized, pilot study was performed in 49 breast cancer patients receiving radiotherapy after breast conserving surgery. Patients were randomized to use a film-forming silicone gel (StrataXRT group) or a moisturizing cream (X-derm ® group). The severity of radiation dermatitis was graded using physiological skin parameters (erythema index, melanin index, and trans-epidermal water loss; TEWL), provider-assessed visual rating scales (CSSP, RTOG, and CTCAE scales) and patient-reported symptoms (dryness, itchiness, burning sensation, and pain). Changes in these parameters from baseline to 4 weeks post-radiotherapy were evaluated every two weeks. Two-way repeated- measures ANOVA with Greenhouse-Geisser correction followed by Bonferroni's post hoc test was used to analyze the difference of changes in the severity of radiation dermatitis. Results Two-way repeated-measures ANOVA revealed different patterns of changes in erythema index (F=3.609, p =0.008) and melanin index (F=3.475, p =0.015). When compared with X-derm group, the StrataXRT group showed significant reductions in erythema index at the end of radiotherapy ( p <0.001) and melanin index at two weeks post- radiotherapy ( p =0.006). There were no significant differences between groups with respect to TEWL,