ESTRO 36 Abstract Book

S167 ESTRO 36 _______________________________________________________________________________________________

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

may lead to better palliation and possibly increase survival with the advantage of a short overall treatment time. The superior soft tissue contrast of MRI might improve tumour contouring and MRI is capable of tumour motion quantification. We want to investigate the technical feasibility and safety of MRI-guided SBRT for LAPC. Material and Methods From July 2013 to January 2016, 20 patients with LAPC or medically unresectable pancreatic cancer without distant metastasis were included in this study (Table). A custom made abdominal corset was manufactured to reduce breathing induced tumour motion. Contouring of the gross tumour volume (GTV) and organs at risk (OARs) was performed on 4D treatment planning CT and multiparametric MRI. A GTV-to-PTV margin of 3 mm was applied. We quantified tumour motion with cine MRI. After treatment planning, the static dose distribution was convolved with the cine MRI based motion trajectory to simulate and evaluate the delivered dose to the GTV, PTV, and OARs. SBRT was carried out up to a dose of 24 Gray in 3 fractions in one week. Online position verification was performed with 4D CBCTs, with 4D matching based on gold fiducial markers at the midventilation position. Results All patients underwent uncomplicated endoscopic fiducial marker placement. Tumours and OARS were clearly visible with contrast enhanced CT and multiparametric MRI (Figure). On the 4D planning CT and on the 4D CBCT scans, the fiducial markers were clearly visible. The corset decreased peak-to-peak tumour motion in craniocaudal direction on average from 11.3 to 7.2 mm. With incorporation of the tumour motion trajectory, the dose distribution was blurred and, in this way, the actual delivered dose was simulated. In all patients, an adequate dose distribution was achieved with acceptable dose in the OARs (Table). Position verification based on 4D marker matching was feasible. No grade 3 or higher treatment related toxicity was observed in these patients to date.