ESTRO 2020 Abstract Book

S258 ESTRO 2020

p=0.047, respectively). No major toxicity was found in either group. Conclusion Lenalidomide-Dexamethasone in association with IMRT in the treatment of solitary plasmacytoma is safe and improves MMFS and PFS. Further prospective and comparative studies are needed to confirm these results OC-0463 Higher baseline SUVmax of 18F-FDG PET-CT indicated worse prognosis in nasal type ENKTL patients X. Xia 1 , Y. Wang 2 , J. Yuan 1 , W. Sun 2 , Y. Lin 1 , F. Ye 1 , X. Ma 2 1 Municipal Hospital Affiliated to Medical School of Taizhou University, Department of Radiology, Taizhou, China ; 2 Fudan University Shanghai Cancer Center, Department of Radiation Oncology, Shanghai, China Purpose or Objective To evaluate the prognostic value of baseline SUVmax of 18F-FDG PET-CT in nasal type Extranodal natural killer/T- cell lymphoma (ENKTL) patients. Material and Methods From January 2010 to December 2015, 141 nasal type ENKTL patients who received radiotherapy or chemoradiotherapy at the Department of Radiation Oncology, Fudan University Shanghai Cancer Center were included. Gender, age at diagnosis, primary site, lymph node status, Ann Arbor stage, ECOG score, lactate dehydrogenase (LDH), B symptoms, PINK score, and baseline SUVmax value of 18 F-FDG PET-CT were recorded. Receiver Operating Characteristic (ROC) curves were used to calculate the perfect cutoff of SUVmax in relation to prognosis. Then the patients were divided into two SUVmax groups (with the perfect cutoff). Clinical distribution differences between the two groups were compared using chi-square test. Associations between the two groups and survival times, including OS (overall survival), PFS (progression free survival), LRFS (local recurrence free survival), DMFS (distant metastasis free survival), were analyzed through univariate and multivariate Cox proportional hazards regression analyses. Survival plots were obtained from Kaplan-Meier analyses, and two curves was compared using log-rank test. Results The median value of SUVmax was 11.67 (range, 2.6-34.6). ROC curves showed that optimal cutoff of baseline SUVmax was 9.65. Patients were divided into two groups: SUVmax<9.65 group and SUVmax≥9.65 group. A higher SUVmax (≥9.65) was more likely to exist in patients with primary sites invading outside of nasal cavity (P<0.001), poorer ECOG scores (P=0.012) and elevated LDH level (P=0.034). Univariate survival analyses indicated that SUVmax≥9.65 was a poor prognostic factor of OS (P=0.038), PFS (P=0.006) and DMFS (P=0.001), but not LFRS (P>0.05). And those results were verified in survival analyses using Kaplan-Meier method. Furthermore, after adjusting for multiple clinical features, multivariate survival analyses showed that SUVmax was no longer a prognostic factor of OS (HR 1.99, 95%CI 0.81-4.88, P=0.135). But a higher SUVmax (≥9.65) still indicated worse PFS (HR 2.6, 95% CI 1.24-5.46, P=0.012) and DMFS (HR 4.58, 95%CI 1.83-11.46, P=0.001) independent from other variables. Conclusion For nasal type ENKTL patients, a higher baseline SUVmax of 18F-FDG PET-CT was associated with more aggressive clinical features. SUVmax≥9.65 was an independent poor prognostic factor of DMFS and PFS. Thus, baseline SUVmax is a valuable tool to help identify patients with higher risk of disease progression.

Proffered Papers: Proffered papers 25 - Clinical implementation of online MRgRT

OC-0464 Quantification and reduction of susceptibility artefacts for a quality assurance phantom in MRgRT E. Hellwich 1,2 , A. Elter 2,3,4 , S. Dorsch 2,3,4 , P. Mann 3,4 , J. Emmerich 2,5 , M. Schäfer 6 , A. Runz 3,4 , S. Klüter 4,7 , C.K. Spindeldreier 4,7 , C.P. Karger 4,8 , J. Debus 1,4,7,9,10,11 , J. Geist 12 1 German Cancer Research Center DKFZ, Clinical Cooperation Unit Radiation Oncology, Heidelberg, Germany ; 2 University of Heidelberg, Faculty of Physics and Astronomy, Heidelberg, Germany ; 3 German Cancer Research Center DKFZ, Medical Physics in Radiation Oncology, Heidelberg, Germany ; 4 Heidelberg Institute of Radiation Oncology HIRO, National Center for Radiation Research in Oncology NCRO, Heidelberg, Germany ; 5 German Cancer Research Center DKFZ, Division of Medical Physics in Radiology, Heidelberg, Germany ; 6 German Cancer Research Center DKFZ, Department of Radiopharmaceutical Chemistry, Heidelberg, Germany ; 7 University Hospital Heidelberg, Department of Radiation Oncology, Heidelberg, Germany ; 8 German Cancer Research Center, Medical Physics in Radiation Oncology, Heidelberg, Germany ; 9 German Cancer Consortium DKTK, partner site, Heidelberg, Germany ; 10 Heidelberg Ion-Beam Therapy Center HIT- Heidelberg University Hospital, Department of Radiation Oncology, Heidelberg, Germany ; 11 National Center for Tumor diseases NCT, Radiation Oncology and Radiation Therapy, Heidelberg, Germany ; 12 Kirchhoff-Institute for Physics, Heidelberg University, Heidelberg, Germany Purpose or Objective In MRI, susceptibility-induced artefacts occur at interfaces of materials with different magnetic susceptibilities, which may lead to image distortions. In this work, a phantom prototype for simultaneous validation of the radiation and imaging isocenter at MR-guided radiotherapy (MRgRT) devices was modified to reduce susceptibility artefacts. The extent of susceptibility-induced distortions was measured and a method of susceptibility adjustment by dissolving salts in the water-filling was investigated. Material and Methods The phantom consists of a metal sphere at the center of a water-filled 3D-printed (VeroClear TM material) cube. Also planes for exact positioning in the MR isocenter and attachment of the metal sphere were printed. The radiation isocenter is defined by the center of the metal spheres' attenuation profile measured by radiochromic films attached to the phantom’s beam exit side. Three different alloys were tested as sphere materials containing mainly copper, lead and tungsten. MRI images were acquired at a clinical 0.35 T and 6 MV MR-Linac (MRIdian® Linac, Viewray Inc., Oakwood, USA) and a diagnostic 1.5 T MAGNETOM Aera/Symphony MRI (Siemens Healthcare GmbH, Erlangen, Germany). The irradiation was performed at the MR-Linac. The spheres’ susceptibilities were measured using a MPMS®-XL magnetometer (Quantum Design, San Diego, USA). According to Wiedemann’s additivity law for the susceptibility of solutions [1], a series of MR measurements with different salt concentrations were performed. The extent of the susceptibility artefacts was evaluated by the calculation of distortion maps [2]. [1] Kuchel et al. 2003, doi: 10.1002/cmr.a.10066 [2] Emmerich et al. 2018, doi: 10.1002/mp.12785