ESTRO 2021 Abstract Book

S143

ESTRO 2021

P. Braam 1 , C. van der Horst 2 , S. Bongers 2 , Y. Versleijen-Jonkers 2 , V. Ho 3 , J. de Wilt 4 , I. Desar 2 1 Radboud University Medical Center, Radiation Oncology, Nijmegen, The Netherlands; 2 Radboud University Medical Center, Medical Oncology, Nijmegen, The Netherlands; 3 Netherlands Comprehensive Cancer Organization, IKNL, Utrecht, The Netherlands; 4 Radboud University Medical Center, Surgery, Nijmegen, The Netherlands Purpose or Objective Myxofibrosarcoma (MFS) is a rare mesenchymal soft tissue sarcoma. MFS is characterized by a high local recurrence (LR) rate together with a higher amount of amputations compared to other soft tissue sarcomas. Robust survival data on the MFS subtype are lacking. We aimed to describe the real life outcomes of a large cohort of MFS patients and to identify prognostic factors. Materials and Methods We obtained clinical data of MFS patients from 2002-2019 using the nationwide database from the Netherlands Cancer Registry (NCR). Survival follow up data was obtained via linkage with local reports from the Dutch municipals Records. More detailed follow-up data, including recurrence status, was available for a subcohort of patients between 2007 and 2011. Analysis of survival were based on Kaplan-Meier models and Log-Rank tests were used to compare differences in survival between groups. Cox regression survival analyses was used to identify the prognostic factors. Results A total of 908 patients was identified of whom 54.2% were male. The median age was 67 years (range 18-98). The extremities were the most common primary localization of the tumour (75.6%), followed by the trunk (20.2%) and head and neck (2.6%). Most patients had MFS grade III (3.4%), 20.7% had grade II and 26.5% had grade I. 92.2% of the patients received surgery as primary treatment, preceded by neoadjuvant radiotherapy (RT) in 20.7% and resulting in a 64.4% complete resection rate. Additional treatment with adjuvant RT was given in 32%. Median overall survival (OS) was 155 months (CI 95% 126-184 months). The five-year OS rate was 67.7%. OS did not improve comparing an early cohort of 2002-2010 with a recent cohort 2011-2019 (p=0.2). Surgery in a sarcoma expertise center was prognostic for a better OS compared to surgery in general hospitals (p=0.02). In multivariable analysis, independent factors negatively affecting OS were age 65, male gender, cancer in medical history, histological grade II and III, tumor size 5cm, deep tumor location , distant metastases at diagnosis, having no surgery and microscopic residual disease after primary treatment. Out of 178 patients, a LR occurred in 38.8% of patients with a median OS of 64.0 months (CI 95% 38.5-89.5), and distant metastases in 28.1% with a median OS of 34.3 months (CI 95% 28.8-39.8). Multivariable analysis identified age 65, deep tumor location, histological grade III, microscopic residual disease and having no adjuvant RT, as prognostic factors increasing the risk of development of LR. Prognostic factors identified after multivariable analysis increasing the risk of distant metastases were female gender, tumor size 5cm, histological grade III and receiving neoadjuvant RT. Conclusion In this largest nationwide cohort so far, survival outcomes and recurrence rates for MFS patients remained poor, emphasizing the need to improve treatment strategies for these patients. A role for sarcoma expertise centers might be suggested. PH-0212 Optimization of intravoxel incoherent motion diffusion MRI for brain tumours biomarkers estimation G. Buizza 1 , M.A. Zampini 1 , G. Sablone 1 , G. Fontana 2 , S. Imparato 3 , G. Riva 4 , A. Iannalfi 4 , E. Orlandi 4 , C. Paganelli 1 , G. Baroni 1,2 1 Politecnico di Milano, Department of Electronics, Information and Bioengineering (DEIB), Milan, Italy; 2 National Center of Oncological Hadrontherapy (CNAO), Clinical Bioengineering Unit, Pavia, Italy; 3 National Center of Oncological Hadrontherapy (CNAO), Radiology Unit, Pavia, Italy; 4 National Center of Oncological Hadrontherapy (CNAO), Clinical Department, Pavia, Italy Purpose or Objective To provide a framework to optimize b-values sets for intravoxel incoherent motion (IVIM) parameters (diffusion D, perfusion fraction f, pseudo-diffusion D*) estimation in deriving accurate imaging biomarkers of brain tumors. Materials and Methods Three sets of parameters were used to simulate noisy IVIM signals in different perfusion regimes (from literature {D,f,D*}-Low:{1e-3mm²/s, 0.05, 1e-2mm²/s}; Medium:{15e-4mm²/s, 0.30, 15e-3mm²/s}; High:{1e- 3mm²/s, 0.30, 6e-2mm²/s}). A segmented fit was performed for b-low ([0 190]s/mm², step:10s/mm²) and b- high ([300 1400]s/mm², step:100s/mm²) b-values ranges. The optimal b-values set was found through an optimization procedure: from thousands of sets of 13 random b-values, estimates errors were computed (σ ₜₒₜ as the sum of relative errors of IVIM parameters: σD, σD*, σf) and candidate sets were chosen as those for which σD ≤ 0.25 for b-high and σ ₜₒₜ ≤ 0.80 for b-low. The 13 values of the optimal sets (b-opt₁₃, one for each regime) were found as the most frequent b-values in b-high and b-low. Optimized sets of 7 b-values (b-opt₇) were obtained via backward elimination: the least frequent b-values of b-opt₁₃ were iteratively eliminated in b-low and b-high ranges to minimize σ ₜₒₜ . Simulations were also performed using 7 b-values used in the clinical practice (b-im=[0 50 100 150 200 400 1000]s/mm²). Relative errors from different perfusion regimes and b-values sets (b-opt₁₃, b-opt₇ and b-im) were compared to evaluate differences between b-values configurations (Kruskall-Wallis test, α=0.05). To evaluate the impact of optimization on patient data, IVIM maps were computed voxel wise through a segmented fit of diffusion MRI data acquired with b-im from patients affected by meningioma (n=9) and skull- base chordoma (n=11). The means of D, f and D* were computed over all patients in white matter (WM) and Poster highlights: Poster Highlights 7: Quantitative functional and biological imaging