ESTRO 36 Abstract Book

S69 ESTRO 36 2017 _______________________________________________________________________________________________

measure the predictive value of high- and low-dose parameters for toxicity in lungs and esophagus, we fitted V5 and V50Gy to RP and grade>=3 radiation esophagitis (RE). Heart dose data was missing for 5 IMRT patients. Results RP and RE are not significantly different between modalities (p>0.1, two-tailed Wilcoxon rank-sum test). The difference between mean doses planned for IMRT and 3DPT plans was tested: Lung V5, V50, V60, V70Gy (in %), esophageal V5Gy, and heart V5, V10Gy are significantly different (p<0.005, two-tailed Wilcoxon rank-sum test). The significant esophageal and heart dose parameters are smaller for 3DPT, lung V5Gy is smaller, while lung V50,V60,V70Gy are larger. 3DPT plan V5 and V50Gy are computed for each OAR and compared to the respective median values of IMRT plans. The percentage of 3DPT plans with V5Gy below or equal to the IMRT median and V50Gy above the IMRT median are reported: <=V5Gy IMRT Median >V50Gy IMRT Median 3DPT Lung 0.93 0.68 Esophagus 0.67 0.49 Heart 0.93 0.54 3DPT plans yield smaller low dose regions in all three OARs. However, 3DPT yields larger high dose regions in the lungs. To assess the relationship between low/high dose regions and toxicity, V5 and V50Gy of lung and heart were fitted to RP, esophageal V5 and V50Gy were fitted to RE:

Conclusion Incidental dose to the cardiac atria and ventricles did not improve RP risk prediction in our cohort of s tage III NSCLC patients as the DVH parameters for lung o utperformed those for the heart. The multivariable mo del containing the variables cardiac comorbidity and MLD is the optimal model for RP prediction in this cohort. OC-0143 Adaptive radiotherapy reduces pneumonitis without increasing the risk of failure in lung cancer A.A. Khalil 1 , M.M. Knap 1 , M.T. Petersen 1 , M. Kandi 1 , H.H. Schmidt 1 , D.S. Møller 2 , L. Hoffman 2 1 Aarhus University Hospital, Department of Oncology, Aarhus C, Denmark 2 Aarhus University Hospital, Department of Medical Physics, Aarhus C, Denmark THIS ABSTRACT FORMS PART OF THE MEDIA PROGRAMME AND WILL BE AVAILABLE ON THE DAY OF ITS PRESENTATION TO THE CONFERENCE. OC-0144 Dosimetric analysis of randomized lung proton and photon plans with respect to radiation toxicity T. Deist 1 , P. Yang 2 , C. Oberije 1 , P. Allen 2 , Y. Luo 2 , Y. Van Wijk 1 , D. Gomez 2 , T. X u 2 , S. Tucker 3 , R. Mohan 4 , S. Hahn 2 , P. Lambin 1 , Z. Liao 2 1 MAASTRO Clinic, Department of Radiotherapy, Maastricht, The Netherlands 2 The University of Texas MD Anderson Cancer Center, Department of Radiation Oncology, Houston, USA 3 The University of Texas MD Anderson Cancer Center, Department of Bioinformatics and Computational Biology, Houston, USA 4 The University of Texas MD Anderson Cancer Center, Department of Radiation Physics, Houston, USA Purpose or Objective Results from a Bayesian-randomized trial on intensity modulated radiotherapy (IMRT) vs. passively scattered 3D proton therapy (3DPT) show no significant difference in protocol failure (i.e., either grade>=3 radiation pneumonitis (RP) or local recurrence within 12 months). We intend to analyze the differences in dose distribution between modalities, relations between dosimetric parameters and radiation-induced toxicities. The objective is to identify dosimetric constraints that would limit normal tissue complications in future trials. Material and Methods We analyzed 149 (57 3DPT, 92 IMRT) randomized trial patients. DVH parameters for 3DPT and IMRT treatment plans were compared for lung, esophagus, and heart. To

There appears to be a stronger relationship between toxicity and high dose regions in the affected OAR. Heart doses have a weaker relationship with RP. Conclusion Tucker et al. (2013) showed that high dose regions in lung tissue in lung IMRT have a pronounced effect on toxicity. This is also observable in this trial cohort of IMRT and 3DPT patients. In order to reduce toxicities, high dose regions in normal tissues need to be reduced. 3DPT reduces low dose regions significantly in all three OARs but high doses regions are significantly higher in the lungs. Future investigations should focus on stricter high dose constraints for 3DPT plans. If such constraints are not achievable due to penumbral and scattering characteristics of protons and the usage of passive scattering techniques, intensity modulated proton therapy should be considered.

Joint Symposium: ESTRO-JASTRO: Oligometastatic disease

SP-0145 Biological rationale and clinical evidence P. Ost 1 1 University Hospital Ghent, Gent, Belgium In 1995, Hellman and Weichselbaum hypoth esized that the number and location of the metastases are an important prognostic factor reflecting the metastatic phenotype and hence prognosis of the cancer patient. They suggested this based on the historical observation