ESTRO 36 Abstract Book

S165 ESTRO 36 2017 _______________________________________________________________________________________________

3 Aarhus University Hospital, Department of Nuclear Medicine & PET Centre and Department of Hepatology and Gastroenterology, Aarhus C, Denmark 4 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus C, Denmark Purpose or Objective 2[ 18 F]fluoro-2-deoxy-D-galactose (FDGal) is a hepatocyte- specific positron emission tomography (PET) tracer. It was used as a marker for hepatocyte function for applying functional treatment planning (FTP) to minimize the radiation dose to the normal liver tissue. We report the results of a cohort of patients treated with FTP- stereotactic body radiotherapy (SBRT) for liver metastases. Material and Methods Fourteen patients referred for SBRT for liver metastases from colorectal cancer were included in the study between December 2013 and August 2016. Nine patients were irradiated for a solitary metastasis and five patients for two (n=4) or three (n=1) metastases. The mean cumulated CTV was 70.3 cc (range 2.0 - 189.7 cc). FDGal PET/CT was performed at baseline and one month post- treatment. The liver was divided into nine iso-functioning volumes based on radioactivity concentration SUV of FDGal on the baseline FDGal PET/CT and transferred to the planning CT using deformable co-registration. The prescribed mean dose to the CTV was 45-60 Gy in 3-6 fractions. The post-treatment FDGal PET/CT was used for evaluation of radiation dose-response for the normal liver tissue. Results FTPs were created and applied for all patients and all plans met the predefined dose-volume constraints with the exception of a soft constraint of mean dose to the liver-CTV that was not met in three patients. Eight patients (57%) were treated with local therapy for liver metastases before inclusion in the present study (surgery n=1; SBRT n=1; combined local therapy n=6. No severe (CTCAE 4.0 grade 3-5) acute morbidity was registered. Teen grade 1 gastrointestinal and six grade 1-2 non- gastrointestinal acute morbidities were registered. No patients had liver-related morbidity. Analysis of the post- treatment FDGal PET/CT revealed a dose-dependent depression in hepatocyte function measured in SUV of FDGal uptake in the irradiated normal liver tissue. Conclusion The study shows feasibility for FTP in patients with colorectal liver metastases referred for SBRT using FDGal PET/CT as a marker for hepatocyte function and the radiation dose to the normal liver tissue was minimized without compromising the organs at risk. The acute morbidity was minimal. H.D. Heerkens 1 , M. Van Vulpen 1 , B. Erickson 2 , O. Reerink 3 , M. Intven 1 , C.A.T. Van den Berg 1 , I.Q. Molenaar 4 , F.P. Vleggaar 5 , G.J. Meijer 1 1 UMC Utrecht, Radiation Oncology Department, Utrecht, The Netherlands 2 Medical College of Wisconsin, Radiation Oncology Department, Milwaukee, USA 3 Isala Clinic, Radiation Oncology Department, Zwolle, The Netherlands 4 UMC Utrecht, Surgery Department, Utrecht, The Netherlands 5 UMC Utrecht, Gastroenterology Department, Utrecht, The Netherlands Purpose or Objective Patients with locally advanced pancreatic cancer (LAPC) show a poor survival due to limited effective therapeutic options. Stereotactic radiotherapy (SBRT) may delay the development of metastasis and physical discomfort, and it PV-0321 MRI guided stereotactic radiotherapy for locally advanced pancreatic cancer

mean pathologic node volume at diagnosis was 3.4±5.8 cm 3 . The mean EBRT and nodal boost doses were 44.3±0.9 Gy and 10.0±2.9 Gy respectively. The mean IGABT contribution to pelvic nodes was 4.2±2.6 Gy. Finally the mean total dose to lymphadenopathies was 55.3±5.6 Gy. Concomitant chemotherapy was administrated in 96.5% of the patients. After a median follow-up of 33.5 months, 20 patients (17.4%) experienced relapses in nodes initially considered pathologic at diagnosis (local relapse). Among them recurrences were observed in a total of 44 nodes (15.3%). The mean time from treatment completion to relapse was 9.0±11.8 months. There was no significant relationship between the dose delivered to pathologic nodes and local control probability (p=0.38). Univariate analyses tested various factors: subtypes (SCC versus others, p=0.35), concomitant chemotherapy (p=0.39), use of SIB (p=0.07), volume at diagnosis (threshold: 3 cm 3 , p<0.0001) and dose (≥ 57.5 Gy, p=0.039). The last three factors were entered in a multivariate analysis. Volume (HR=8.2, 4.0-16.6, p<0.0001) and dose (HR=2, 1.05-3.9, P=0.034) remained independent, whereas SIB was not (p=0.99). Subsequent Probit analysis combining dose and volume showed significant relationships with the probability of local control (Figure).

Conclusion The initial volume was the main prognostic factor of control in pathologic lymph nodes. A dose superior to 57.5 Gy was also associated with a better local control probability. Further studies are required to refine these findings.

Poster Viewing : Session 7: Upper and lower GI

PV-0320 Stereotactic body radiotherapy for liver metastases based on functional treatment planning M.M. Fode 1 , J. Petersen 2 , E. Worm 2 , M. Sørensen 3 , K. Bak-Fredslund 3 , S. Keiding 3 , M. Høyer 4 1 Aarhus University Hospital, Department of Oncology, Aarhus C, Denmark 2 Aarhus University Hospital, Department of Medical Physics, Aarhus C, Denmark