ESTRO 38 Abstract book

S1151 ESTRO 38

(p=0,2845) and nGTV-

nGTV-MR (p=0,1141), nGTV-PET 30%

Results At the time of CT simulation, all patients expressed a preference for the arms-down position in terms of comfort. Both physicians described a greater degree of difficulty when contouring the level I axilla in the arms- down position. Difficulty in plan generation between arms-up and arms-down cases was similar. Overall, the arms-down plans conferred a slightly lower target coverage, but within a clinically acceptable range. Treatment positioning using surface imaging presented equal challenges in either position. Conclusion This study highlights the appropriateness of treating breast patients in an arms-down position when using proton therapy. EP-2085 PET/MR in GTV delineation in patients with carcinoma of the tongue N. Samołyk-Kogaczewska 1 , E. Sierko 2 , K. Zuzda 3 , P. Gugnacki 3 , P. Szumowski 4 , M. Mojsak 4 , J. Burzyńska- Śliwowska 5 , T. Filipowski 1 , M.Z. Wojtukiewicz 6 , D. Jurgielewicz 4 1 Comprehensive Cancer Center of Białystok, Department of Radiotherapy, Białystok, Poland ; 2 Medical University of Bialystok- Comprehensive Cancer Center, Department of Oncology- Department of Radiotherapy, Białystok, Poland ; 3 Medical University of Bialystok, Scientific Student's Association affiliated with Department of Oncology, Białystok, Poland ; 4 Medical University of Bialystok, Laboratory of Molecular Imaging- Nuclear Medicine Department, Białystok, Poland ; 5 Comprehensive Cancer Center of Białystok, Department of Diagnostic Imaging, Białystok, Poland ; 6 Medical University of Bialystok, Department of Oncology, Białystok, Poland Purpose or Objective Evaluation of accuracy and usefulness of 18-fluor-labeled fluorodeoxyglucose (PET) and magnetic resonance (MR) hybrid in gross tumor volume (GTV) delineation during radiotherapy planning in patients with carcinoma of the tongue. Material and Methods Computed tomography (CT) and PET/MR examination were made in group of 10 patients (pts) with squamous cell carcinoma (SCC) of the tongue. The GTV for primary tumor and lymph nodes (nGTV) were defined on CT (GTV- CT) and compared to GTVs obtained from PET (GTV-PET) and MR (GTV-MR) images. Two methods of GTV determination were used: visual interpretation of CT, PET (GTV-PET vis ) and MR images and quantitative automatic method (Syngovia, Siemens) based on a chosen threshold value (20%, 30%, 40%, 50%) of SUV max from PET examination (GTV-PET 20% , GTV-PET 30% , etc.). Differences in GTV values obtained from CT, PET and MR studies were statistically analysed. The level of significance was considered as p<0.05. The GTV-CT was used as the reference. Results The 80% of GTV-MR and 40% of GTV-PET vis were larger than GTV-CT. Respectively, 20% of GTV-MR and 60% of GTV- PET vis were smaller than GTV-CT. Taking into account all threshold measurements - 70% of volumes were smaller than GTV-CT. GTV-PET 30% (p=0,2026) were the most closely related volumes to GTV-CT from all threshold method in 50% of patients. GTV-PET vis (p=0,5750) generated the most similar volumes in relation to GTV-CT from all PET measurements. Comparing to nGTV-CT - 70% of nGTV-MR and 20% of nGTV-PET vis were larger. Remaining nGTV-MRI and nGTV-PET vis measurements were smaller than nGTV- CT. Measurements of all thresholds nGTVs were smaller than nGTV-CTV in 52,5% of cases. nGTV-PET 20% were the most closely related volumes to nGTV-CT in 40% of the cases. Statistical analysis shown that nGTV-PET 20% (p=0,0468), nGTV-PET vis (p=0,0166) and nGTV-PET 50% (p=0,0166) diverge significantly from nGTV-CT results.

PET 40%

(p=0,5076) were the most significantly related with

nGTV-CT. Conclusion

Combination of PET/MR provide better accuracy in GTV delineation in radiotherapy planning of pts with SCC of the tongue than other standard imaging methods. The most frequently matching threshold value in PET/MR was 30% of SUV max for primary tumor delineating and 30% and 40% of SUV max for nGTV estimation. EP-2086 Innovative hybrid 18FDG-PET/MR in GTV delineation in locally advanced oral cavity cancer patients N. Samołyk-Kogaczewska 1 , E. Sierko 2 , D. Dziemiańczyk- Pakieła 3 , B. Nowaszewska 3 , K. Zuzda 4 , J. Burzyńska- 1 Comprehensive Cancer Center of Białystok, Department of Radiotherapy, Białystok, Poland ; 2 Medical University of Bialystok- Comprehensive Cancer Center, Department of Oncology- Department of Radiotherapy, Białystok, Poland ; 3 Medical University of Bialystok, Department of Maxillofacial and Plastic Surgery, Białystok, Poland ; 4 Medical University of Bialystok, Scientific Student's Association affiliated with Department of Oncology, Białystok, Poland ; 5 Comprehensive Cancer Center of Białystok, Department of Diagnostic Imaging, Białystok, Poland ; 6 Medical University of Bialystok, Laboratory of Molecular Imaging- Nuclear Medicine Department, Białystok, Poland ; 7 Medical University of Bialystok, Department of Oncology, Białystok, Poland Purpose or Objective The aim of the study was to assess possibilities offered by innovative hybrid of 18 FDG-PET/MR in GTV definition during RT planning in patients (pts) with locally advanced carcinoma of the oral cavity. Material and Methods A group of 15 pts with squamous cell carcinoma of the oral cavity underwent contrast-enhanced CT (Aquilion ONE, Toshiba) and PET/MR (3T Siemens Biograph mMR) examination. Delineation of GTV was made using two methods: visual interpretation of CT (GTV-CT), PET (GTV- PET vis ) and MR (GTV-MR) images, as well as quantitative automatic method (Syngovia, Siemens) based on a chosen threshold value (20%, 30%, 40%, 50%) of SUV max from PET examination (GTV-PET 20% , GTV-PET 30% , etc.). Obtained volumes of primary tumor were compared and differences were statistically analyzed. The level of significance was considered as p<0.05. The GTV-CT was used as the reference. Results In 80% of cases of GTV-MR and 100% of GTV-PET vis volumes were larger than reference GTV-CT. Only in three patients GTV-MR was smaller than GTV-CT. The 40% of all PET automatic threshold measurements were larger than results based on CT images. Respectively - 60% of volumes from quantitative automatic method were smaller than GTV-CT. Statistical analysis shown that the most closely related results to GTV-CT were obtained from MR imaging (p=0,0796), GTV-PET 30% (p=0,8927), GTV-PET 40% (p=0,3452) and GTV-PET 50% (p=0,0796). On the other hand GTV-PET vis (p=0,0431) and GTV-PET 20% (p=0,0431) diverge significantly from volumes based on CT images. Conclusion Quantitative automatic method based on a chosen threshold value combined with MR imaging seems to be better delineation method in cases of locally advanced cancer of oral cavity. Hybrid PET/MR supports the optimal determination of volumes for RT treatment. Although, further studies are needed. EP-2087 Probabilistic Modeling of Patient Setup Time in VMAT Treatments Based on Anatomical Regions Śliwowska 5 , P. Szumowski 6 , D. Jurgilewicz 6 , T. Filipowski 1 , M.Z. Wojtukiewicz 7 , M. Mojsak 6