ESTRO 2020 Abstract Book

S338 ESTRO 2020

systemic treatment and higher anxiety levels were associated with impaired body image.

PH-0600 Distribution patterns of lymphatic metastases: influence of axillary lymph node dissection C.A.M. Schleibinger 1 , K.J. Borm 1 , J. Voppichler 1 , M. Düsberg 1 , M. Oechsner 1 , S.E. Combs 1 , M. Duma 1,2 1 Klinikum rechts der Isar, Department of Radiation Oncology- Technical University of Munich TUM- Ismaninger Str. 22, Munich, Germany ; 2 University Hospital of the Friedrich-Schiller University, Department of Radiotherapy and Radiation Oncology- Bachstraße 18, Jena, Germany Purpose or Objective In 2018, a study on the distribution patterns of PET positive lymph node metastases (LNM) in breast cancer patients (Borm KJ et al., IJROBP 2018) was published. Therein, LNM of patients with recurrent breast cancer were analysed. The aim of the current study was to assess whether the pattern of lymph node recurrences differs between patients with prior axillary lymph node dissection (ALND) vs. no prior ALND. Material and Methods 171 patients with recurrent breast cancer out of 235 patients comprised in the original study were included in the current study. A detailed analysis of the medical records was performed in order to record the treatment prior to diagnosis of the LNM. Furthermore, information about the primary tumor of the patients (e.g. stage, grading, biology) was collected. Reliable and comprehensive data could be collected for 134 of 171 patients. The LNM were allocated to two different groups: ALND vs. no ALND. The LNM in each group were compared with regard to the distribution pattern and size of the LNM and the presence of distant metastases. Color-coded heatmaps marking hotspots of LNM in a CT-template were created (figure 1). Results The ALND group consisted of 131 LNM (63 patients), the no ALND group of 136 LNM (58 patients). Most patients had distant metastases at the time of the recurrence (ALND 63,49%; no ALND 75,86%). The average number of LNM per patient was 2,08 for group ALND and 2,34 for group no ALND. In both groups, LNM occurred mainly in Level I (ALND n=40: 30,53%; no ALND n= 79: 58,09%) and the supraclavicular region (ALND n=27: 20,61%; no ALND n=26: 19,12%). LNM in Level II, III and the internal mammary region occurred more often after ALND (Level II: ALND n=16: 12,21%; no ALND n=10: 7,35% ; Level III: ALND n=22: 16,79%; no ALND n=10: 7,35%; internal mammary region: ALND n=20: 15,27%; no ALND n=10: 7,35%). Figure 1 depicts hotspots of LNM of group ALND (a) compared to LNM of group no ALND (b).

Conclusion LNM occur with different frequencies in all axillary levels. The patients that underwent axillary dissection had less LNM in L I than the patients that did not undergo ALND. Further, the ALND patients had LNM in Level II, III and the internal mammary region more often. The current atlas reveals areas where LNM need to be expected after ALND. These areas need special consideration during regional node irradiation in the primary situation after ALND. PH-0601 Dosimetric Parameters Associated with Esophagitis in Regional Nodal Irradiation for Breast Cancer J. Bazan 1 , K. Kuhn 1 , E. Healy 1 , S. Jhawar 1 , S. Beyer 1 , D. DiCostanzo 1 , J. White 1 1 The James Comprehensive Cancer - The Ohio State University, Radiation Oncology, Columbus, USA Purpose or Objective The esophagus lies in close proximity to the supraclavicular nodal region, a target volume in regional nodal irradiation (RNI)/postmastectomy radiation therapy (PMRT). However, acute esophagitis rates are often not reported. We use a planning target volume (PTV)-based, dose volume analysis (DVA)-driven approach to RNI/PMRT using 3D conformal radiation therapy (3DCRT) or inverse- planned intensity modulated radiation therapy (IMRT) as needed to meet planning objectives. We set to determine the rate of Grade 2 (symptomatic) esophagitis (G2E) with a goal of identifying potential dose constraints to minimize this toxicity. Material and Methods We identified patients that received RNI/PMRT from 1/2013-6/2019. Patients received conventional fractionation (2 Gy/day to 50 Gy) to the breast/chestwall, axillary, supraclavicular, and internal mammary chain PTVs as per the RTOG Breast Atlas. We divided the patients into training (1/2013-12/2016) and validation (1/2017- 6/2019) cohorts. Our primary endpoint was the G2E rate, which we verified by identifying patients that received sucralfate and/or a viscous lidocaine/diphenhydramine/magnesium&aluminum hydroxide mixture during radiation. We retrospectively contoured the esophagus from the caudal edge of the cricoid cartilage to the carina and recorded the mean esophageal dose and V10, V20, V30, V40, and V50. Patients in the training cohort were dichotomized by the median value for the esophageal parameters and logistic regression analysis was used to test for associations between esophageal dose and G2E. Parameters identified as associated with G2E (p<0.05) in the training cohort were