ESTRO 38 Abstract book

S18 ESTRO 38

(n=22, 45%) or without postoperative radiotherapy. MCPyV DNA prevalence, DNA integration status and viral load were determined by virus-specific quantitative real-time PCR. Immune marker expression and MCPyV characteristics were correlated with clinicopathological factors and overall survival (OS). Results Median age at diagnosis was 74 (range 42-100) and 51% of the patients were female. 1-, 3- and 5-years OS rates were 65%, 33% and 25%, respectively. Positive MCPyV status was recorded in 79% of the patients and was associated with female gender (p=0.033). Further, tumor localization (head and arms vs. trunk) positively correlated with PD-L1 status as well as combined expression of CD8+/PD-L1 (p- values: 0.011 and 0.038). Stromal TILs correlated significantly with both PD-L1 expression (p=0.010) and N- stage (p=0.037). Also, N+ stage inversely correlated with TILs (p=0.048). A high viral load was significantly associated with worse OS (p=0.026) and high intratumoral CD8+ infiltration with improved OS for the entire cohort A High MCPy DNA viral load was associated with impaired OS and high intratumoral TILs with improved OS. Furthermore, stromal TILs positively correlated with PD- L1 status, possibly opening new future perspectives for combining treatment approaches such as RT and immune- checkpoint inhibitors. (p=0.045). Conclusion SP-0050 What is left from dose painting when adding all uncertainties M. Alber 1 1 Heidelberg University Clinic, Radiation Oncology, Heidelberg, Germany Abstract text Multiple levels of dose prescription to the target volume (simultaneous integrated boost, SIB) and highly conformal, yet inhomogeneous dose escalation to small targets (such as in stereotactic body radiotherapy) are becoming rather common in modern radiotherapy. Dose painting (DP) is in essence an image-guided SIB, so it is reasonable to assume that planning- and delivery-related uncertainties play no greater role in DP than in geometry-guided SIB. It is the element of biological guidance that adds the essential layers of uncertainty. It is instructive to follow a thought experiment that starts with an indiscriminate, geometric SIB to the core target volume (usually the GTV) with the appropriate prescription (to be addressed later). Then, what image information is required to shape the SIB into DP by chipping away dose? The locations where dose can be reduced are tied to the true negative rate (absence of the biological feature) and thus to specificity, while the level of de-escalation is tied to the false negative rate (missing the biological feature) and thus to sensitivity. Thus, low specificity enlarges the boosted volume, low sensitivity forces the dose spread smaller to limit tumour control loss by underdosing. To arrive at the DP prescription, it is sufficient to demand optimum use of the image information content; no sophisticated biological modelling is required. An imaging modality may appear to be very specific to a particular trait of a tumour, but this does not mean that it is specific to therapy resistance. For example, pre- treatment hypoxia image information may be invalidated by re-oxygenation during therapy, or further unknown tumour characteristics may play a large role in therapy resistance. Thus, any attempt to model tumour response Symposium: Challenging dose painting: Are we really painting what we aim to or the better outcome is only linked to higher dose spots within the CTV?

mastectomy + RT, and 42.3% with lumpectomy + RT. The median RT dose was 46.8 Gy. 85.6% received chemotherapy. There were no significant differences in characteristics between RS and RR patients (p>0.05). Median follow-up was 7.6 years (range 0.21-17.2). There were 10 locoregional recurrences, 15 distant metastases, and 16 deaths. All results of KM analyses are included in the accompanying table. Among all patients, radiophenotype predicted for all outcomes as RS had superior LRFS, DMFS, OS and PFS. Radiophenotype remained predictive for outcomes among RT-treated patients, as RS patients had superior LRFS, DMFS, OS, and PFS compared to RR patients. In contrast, radiophenotype did not predict for outcomes in patients not treated with RT as there were no significant differences in LRFS, DMFS, OS, or PFS. In RT-treated patients, radiophenotype (p=0.034) and surgery type (p=0.012) were associated with PFS and both remained significant on MVA (RR vs RS, HR 4.6 95% CI 1.01-20.48, p=0.048) (lumpectomy vs mastectomy, HR 0.29 95% CI 0.10-0.83, p=0.021). In non- RT patients, no factors predicted for PFS on MVA.

Conclusion In this cohort of consecutively treated patients, we show that RSI radiophenotype predicts for outcomes in TNBC and is specific to RT-treated patients. Patients with radioresistant TNBC have poor outcomes and may benefit from treatment intensification, warranting further prospective validation. PV-0049 Merkel cell polyoma viral load predicts overall survival in patients with Merkel cell carcinoma J. Mueller-von der Gruen 1 , R. Winkelmann 2 , M. Meissner 3 , U. Wieland 4 , S. Silling 4 , D. Martin 1 , E. Fokas 1 , C. Rödel 1 , F. Rödel 1 , P. Balermpas 5 1 University of Frankfurt, Department of Radiation Oncology, Frankfurt, Germany ; 2 University of Frankfurt, Dr. Senckenberg Institute of Pathology, Frankfurt, Germany; 3 University of Frankfurt, Department of Dermatology, Frankfurt, Germany; 4 University of Cologne, Institute of Virology- National Reference Center for Papilloma‐ and Polyomaviruses, Cologne, Germany ; 5 University Hospital of Zürich, Department of Radiation Oncology, Zürich, Switzerland Purpose or Objective Merkel cell carcinoma (MCC) is a rare but aggressive neuroendocrine tumor of the skin and its tumorigenesis is linked to the presence of clonally integrated Merkel cell polyomavirus (MCPyV) in up to 80% of the cases. The aim of this study was to determine the prognostic value of quantitative MCPyV viral load and lymphocytic infiltration. Material and Methods CD8+ tumor infiltrating lymphocytes (TILs) and PD-L1 status were assessed using immunohistochemistry in FFPE tissue obtained from 49 patients with MCC treated with