ESTRO 2021 Abstract Book

S564

ESTRO 2021

Conclusion This study did not create evidence for setting a JCI accuracy threshold level to help reduce clinician intervention. The variations in clinician assessment of auto-segmentation accuracy were significant and highlighted the need for an objective and standardized evaluation method to select clinically acceptable auto- contouring models.

PD-0733 Tolerance of adjuvant moderate hypofractionated whole breast RT with simultaneous integrated boost

L. Hoeng 1 , O. Unterkirhere 1 , A. Kaever 1 , S. Abbeel 1 , C. Glanzmann 1 , G. Studer 1 1 Cantonal Hospital Lucerne, Department of Radiation Oncology, Lucerne, Switzerland Purpose or Objective

The purpose of this study was to evaluate early/intermediate treatment tolerance in patients undergoing postoperative moderate hypofractionated whole breast radiotherapy with simultaneous integrated boost (SIB- mhWBRT) following breast-conserving surgery (BCS). Materials and Methods SIB-mhWBRT for breast cancer patients was introduced in our department in July 2017. This prospective study includes 391 patients treated with SIB-mhWBRT for invasive breast cancer (n=361; pT1(198), pT2 (156), pT3 (4), pT4a (2)/,Tx (2), N0-3, M0) and/or ductal carcinoma in situ (DCIS, n=30) after BCS until April 2020. Mean age was 60 years (range 27–88). Mean/median follow-up was 18/16 months (range 1–38). SIB-mhWBRT was applied with 40 Gy in 15 daily fractions over 3 weeks with a SIB dose to the tumor bed of 48 Gy, delivered either as 3D conformal radiotherapy (3D-CRT, n=369), intensity-modulated radiotherapy (IMRT, n=4) or volumetric-modulated arc therapy (VMAT, n=18). Since 05/2018 also patients indicating for lymphatic pathway irradiation were included (n=62). Follow-up data including objective assessment of baseline parameters and treatment-related outcomes as well as subjective patient reported outcome measures (PROMs) was recorded and reported. Ethical approval is available. Results Skin toxicity (including erythema, desquamation, necrosis/ ulceration, breast edema and bleeding) for grades 0/1/2/3 was distributed as 24.3/61.8/13.6/0.3% at the completion of treatment. The most common acute toxicities at completion of treatment were erythema and breast edema. The only patient with a documented grade 3 bleeding presented this already before start of radiotherapy. 6-months follow-up data was available for 225 patients: with fibrosis grade 0/1/2 in 75.6/20.0/4.4%, skin telangiectasia grade 0/1/2 in 95.6/4.0/0.4%, pigmentation changes grade 0/1/2 in 71.0/27.7/1.3% cases. Patient-reported cosmetic results 6 months post treatment were evaluated in 55.0/41.7/2.3/0.9% cases as excellent/good/fair/poor. Results of 1-year follow-up (available from 137 patients) were comparable: fibrosis grade 0/1/2 in 78.1/20.4/1.5%, no skin telangiectasia (only grade 0), pigmentation changes grade 0/1/2 in 78.7/20.6/0.7% cases. 1-year patient- reported cosmetic results were evaluated in 62.2/34.1/3.7% as excellent/good/fair. 31 patients examined on the 2-year follow-up visit presented with fibrosis grade 0/1 in 93.5/6.5%, pigmentation changes grade 0/1/2 in 80.6/16.1/3.2%. PROM of cosmetic results were evaluated in 59.4/34.4/3.1/3.1% as excellent/good/fair/poor. Ipsilateral breast tumor recurrence developed in 2/391 patients (0.5%) (one in-boost, one marginal to the 40 Gy volume, both triple negative), distant metastatic disease developed in 6 patients (1.5%) at the time of this analysis. No cancer related mortality was observed so far. Conclusion We found a high subjective and objective early/intermediate treatment tolerance of SIB-mhWBRT. This short term regimen offers substantial patient comfort and improves institutional efficacy. PD-0734 Validating Brain Metastases Velocity for survival prediction in patients treated with radiosurgery M. Mayinger 1 , K. Borsky 1 , J. Kraft 1 , S. Frei 1 , L.S. Stark 1 , J. van Timmeren 1 , S. Tanadini-Lang 1 , M. Guckenberger 1 , N. Andratschke 1 1 University Hospital Zurich, Radiation Oncology, Zurich, Switzerland Purpose or Objective Brain Metastases Velocity (BMV) is a recently developed prognostic tool taking brain metastases occurrence dynamics into account. So far, there are three different BMV scores considering the velocity of first occurrence of brain metastases (initial BMV; iBMV) or the recurrence of brain metastases after brain-directed therapy (classical BMV; cBMV and volumetric BMV; vBMC). The aim of our study was to validate all three scores in a patient cohort treated for brain metastases with stereotactic radiotherapy. Materials and Methods We retrospectively evaluated medical records of 386 patients with BM disease receiving stereotactic radiation therapy between January 2014 and December 2019. iBMV, cBMV, and vBMV were calculated. Kaplan-Meier survival curves were used to compare overall survival (OS). Results After a median follow‐up of 14 months (interquartile range: 5 –31), 1 year survival rate was 53%. 183 patients received a minimum of two treatments and 33 at least three treatments (range: 1-7 courses). The iBMV (including all 386 patients; p = 0.75) and the vBMV (104 patients where brain metastases volume was available; p = 0.9) could not sufficiently stratify the patients into different risk groups. The cBMV determined for 183 patients with distant brain failure, was able to significantly separate the different risk groups regarding OS (p < 0.001). At baseline, univariate analysis revealed the extracranial metastatic disease status and GPA to be significant predictors for OS. At first distant brain failure (DBF) extracranial metastatic disease status, karnofsky performance status, GPA and RPA represented prognostic factors. Poster discussions: Poster discussion 2: CNS