ESTRO meets Asia 2024 - Abstract Book

S73

Interdisciplinary – Breast

ESTRO meets Asia

Taylor ME, Perez CA, Halverson KJ. Clinical Original Contribution FACTORS INFLUENCING COSMETIC RESULTS AFTER CONSERVATION THERAPY FOR BREAST CANCER. Radiat Oncol 1995;31:753–764.

Pezner RD, Patterson MP, Lipsett JA, et al. Factors affecting cosmetic outcome in breast-conserving cancer treatment - objective quantitative assessment. Breast Cancer Res Treat 1991;20:85–92. https://doi.org/10.1007/BF01834638. Janssen S, Glanzmann C, Lang S, et al. Hypofractionated radiotherapy for breast cancer acceleration of the START A treatment regime: intermediate tolerance and efficacy. Radiat Oncol 2014;9:165. https://doi.org/10.1186/1748 717X-9-165.

100

Proffered Paper

Strong continuous thermal dose-effect relationship in postoperative recurrent breast cancer patients

C. Paola Tello Valverde 1 , Akke Bakker 1,2 , M. Willemijn Kolff 1 , Geertjan van Tienhoven 1 , H. Petra Kok 1 , Ben J. Slotman 1 , Konstantinos Pateras 3 , Hans Crezee 1 1 Department of Radiation Oncology, Amsterdam UMC, Amsterdam, Netherlands. 2 Department of Oncology, Princess Máxima Center, Utrecht, Netherlands. 3 Faculty of Public and One Health, Laboratory of Epidemiology & Artificial Intelligence, University of Thessaly, Karditsa, Greece

Purpose/Objective:

Mild hyperthermia (39-43°C) combined with re-irradiation improves complete response rate compared with re irradiation alone in locoregional recurrent (LRR) breast cancer. 1,2,3 Observational studies analyzing a dichotomized hyperthermia thermal dose (TD) parameter showed in various studies that higher hyperthermia TD was associated with better tumor response rate compared with a lower TD. 4,5,6 However, analyzing the TD-effect relationships utilizing a continuous TD parameter is more powerful, but has never been done so far. We therefore investigated the effect of a continuous TD parameter on locoregional control (LRC) in patients with LRR breast cancer treated with postoperative re-irradiation and hyperthermia. In this study, we retrospectively analyzed the data of 112 women with LRR breast cancer treated in 2010-2017 with postoperative re-irradiation 8x4Gy (n=34) or 23x2Gy (n=78), combined with 4-5 weekly hyperthermia sessions guided by invasive thermometry. Among possible parametrizations of CEM43 (cumulative equivalent minutes at 43°C), including the TD parameter based on time-temperature exposures, the logarithm of the session with the highest invasively measured dose CEM43T50 (median CEM43) was selected based on Weibull univariate and stepwise regression analyses. The best fitted recurrence-free survival model was further analyzed under a Bayesian paradigm, assuming three informative priors (continuous highest CEM43T50, tumor location breast/chest wall and lymph node involvement). In addition we also performed a logistic regression analysis as a means to illustrate locoregional control and the highest CEM43°CT50 TD in a dose-effect relationship curve. Material/Methods:

Results:

Twenty-four patients (21.4%) developed an infield recurrence; the median time to recurrence was 3.4 years (interquartile range (IQR) 2.7–4.6 years). Median highest session CEM43T50 was 7.2 minutes (equivalent to a