ESTRO 36 Abstract Book

S266 ESTRO 36 2017 _______________________________________________________________________________________________

smokers. We believe the presented failure-type specific models are a highly relevant decision support aid to supplement the inclusion criteria of clinical trials. References: 1. J. Benichou, M.H. Gail, Biometrics. 46 (1990). 2. P. Blanche, J-F. Dartigues, H. Jacqmin-Gadda, Statistics in Medicin e. 32 (2013). PV-0510 FMISO-PET/CT and functional MRI parameters as biomarkers during chemoradiation of HNSCC H. Bunea 1 , A. Bunea 1 , N. Wiedenmann 1 , C. Stoykow 2 , M. Mix 2 , H. Rischke 1 , M. Langer 3 , P. Meyer 2 , M. Bock 4 , A. Grosu 1 1 University Medical Center Freiburg, Department of Radiation Oncology, Freiburg, Germany 2 University Medical Center Freiburg, Department of Nuclear Medicine, Freiburg, Germany 3 University Medical Center Freiburg, Department of Radiology, Freiburg, Germany 4 University Medical Center Freiburg, Department of Medical Physics, Freiburg, Germany Purpose or Objective Tumor hypoxia in squamous cell carcinoma of the head and neck (HNSCC) is associated with poor prognosis. In the following study, the dynamics of hypoxia during chemoradiation (RCTx) is detected with FMISO PET/CT and correlated to perfusion MRI parameters. Perfusion-weight MRI parameters can be correlated with tumor hypoxia and thereby have the potential to serve as predictors of treatment failure. In particular, the volume transfer constant between plasma and interstitial space K trans is an indirect measure of the capillary permeability and blood flow. High skewness of K trans is associated with good treatment response, whereas primary tumors with lower K trans values have a poor prognosis (Shukla-Dave et al., 2012). A subsequent rise of K trans , v e (fractional volume of the extracellular, extravascular space) during RCTx is associated with a good response to treatment. Material and Methods A prospective serial imaging study was conducted in patients undergoing definitive RCTx (70 Gy, concomitant cisplatin) for HNSCC: in weeks 0, 2 and 5 3T-MRI and FMISO PET were acquired. Tumor hypoxia was assessed in FMISO PET 2.5 h p.i. Gross tumor volume in MRI (GTV MRI ) was defined as the area of high signal on T2-weighted images using the T1-weighted images for anatomic cross reference. Perfusion parameters K trans and v e were calculated from a dynamic T1-weighted study after contrast agent injection. Hypoxic subvolume (HSV) of GTV MRI was defined after normalization to the FMISO background in the contralateral sternocleidomastoid muscle, thresholded with 1.4. Volumetric parameters between weeks 0, 2 and 5 were compared and related to treatment response in terms of local recurrence (LR) and stable disease (SD). Statistical analysis was done with Spearman correlation. Before t-test analysis, normal sample distribution was confirmed with Shapiro–Wilk test. Results Between 2014 and 2015 10 male patients, treated for HNSCC with RCTx, were included. All patients received a total dose of 70 Gy. In total, 30 FMISO-PET/CT data sets and 27 MRI data sets were obtained. Mean follow up (FU) was 14.6 months (4 - 28 months). In weeks 0-5, patients with LR showed a mean K trans -decrease of 19%, whereas in weeks 0-2 an increase of SUV max (57 %) was shown. Patients with SD showed K trans -increase (36 %) and SUV max -decrease (-61 %). HSV diminished in all patients. The correlation analysis was significant between Δ GTV MRI and Δ K trans in week 0-2 (p=0.037) and between Δ SUV max (week 0-5) and Δ K trans (week 0-2), p=0.045. Conclusion As was previously shown we conclude that changes in SUV max are crucial in week 2. In our limited patient cohort and the short FU, we found that a decrease in K trans might

indicate a poorer outcome. Finding markers in bioimaging may allow individualization of treatment by dose painting and adaptive radiotherapy. PV-0511 Fitting NTCP models to patient reported xerostomia and dysphagia after H&N radiotherapy to 60Gy P. Mavroidis 1 , A. Price 1 , D. Fried 1 , M. Kostich 1 , R. Amdur 2 , W. Mendenhall 2 , C. Lu 2 , S. Das 1 , L.B. Marks 3 , B. Chera 3 1 University of North Carolina, Radiation Oncology, Chapel Hill, USA 2 University of Florida Hospitals, Radiation Oncology, Gainesville- FL, USA 3 University of North Carolina & Lineberger Comprehensive Cancer Center- University of North Carolina Hospitals, Radiation Oncology, Chapel Hill, USA Purpose or Objective To determine the correlation between different dosimetric indices of salivary glands and pharyngeal constrictors with patient reported xerostomia and dysphagia 6- and 12- months after de-intensified chemoradiotherapy. To estimate the respective radiobiological parameters of four NTCP models regarding xerostomia and dysphagia, respectively. Material and Methods Forty-three patients were treated on a prospective multi- institutional phase II study involving patients with favorable risk, HPV-associated oropharyngeal squamous cell carcinoma. All patients were treated with IMRT to 60 Gy with concurrent weekly intravenous cisplatinum (30 mg/m2). The patient reported outcome version of the CTCAE was used to record the severity of patients’ xerostomia and dysphagia (pre- and post-treatment). A change in severity (from baseline) of ≥ 2 was used as response threshold. Individual patient dosimetric data of salivary glands (as combined and separate structures) and pharyngeal constrictors (as combined and separate sections) were correlated with xerostomia and dysphagia (at 6 and 12 months post-treatment). The Lyman-Kutcher- Burman (LKB), Relative Seriality (RS), Logit and Relative Logit (RL) NTCP models were used to fit the patients’ data. The ability of different dosimetric indices to discriminate and classify patient outcomes was assessed through the area under the Receiver Operating Characteristic (ROC) curve (AUC) and linear regression analysis. The goodness-of-fit of the different models was assessed through the maximum of the log-likelihood function, normal error distribution and Akaike information criterion (AIC). Results The V15-V55 of the combined contralateral glands correlated well with xerostomia (AUC = 0.83-0.86). Similarly, at 12 months, the metrics V10-V17 were the best predictors of xerostomia (AUC = 0.82-0.87). The patient with dysphagia had V55 = 88.7±12.8 (%) to the superior pharyngeal constrictor compared to a V55 = 76.2±12.7 (%) for the patients without the symptom. The points V55-V60 had the highest correlation with dysphagia (AUC = 0.70- 0.75). The AIC values of the different NTCP models ranged between 43.7-44.9 in the case of the combined contralateral glands and 38.1-38.9 in the case of the superior pharyngeal constrictors. For the combined contralateral glands, the NTCP threshold ranges between 70-74% for statistical Odd ratios (OR) ranging between 7.3- 8.0.