Purpose/Objective(s): Stereotactic Body Radiation Therapy (SBRT) is an emerging treatment option for pancreatic cancer. The prescription concept termed Simultaneous Integrated Protection (SIP) allows to deliver high radiation doses within a few fractions to the tumor while sparing the surrounding critical organs at risk (OARs) located very close to the target. The aim of this study was to evaluate the effectiveness, in terms of local control rate (LCR), progression-free survival (PFS) and overall survival (OS), as well as SBRT toxicity in unresectable pancreatic cancer patients (pts)

Materials/Methods: We retrospectively reviewed 25 pts treated from October 2016 to October 2017. 19 (76%) presented with locally advanced disease and 6 (24%) with local recurrence after surgery. 19 pts received induction chemotherapy prior to SBRT. For each patient a custom made abdominal compressor was used to reduce breathing induced tumor motion. Contouring of the gross tumor volume (GTV) was performed by a 4 phase contrast-enhanced simulation computer tomography (CT). The Internal Target Volume (ITV) was defined as the envelope of the GTVs from each CT phase. An ITV-to-PTV (Planning Target Volume) margin of 5 mm was applied. For the OARs (duodenum, stomach, bowel) we used a 3 mm expansion planning organ at risk volume (PRV). SBRT was delivered in 5 consecutive daily fractions, prescribing 30 Gy to the PTV (6 Gy/fraction), while simultaneously delivering 50 Gy (10 Gy/fraction) inside the ITV. SIP was generated prescribing 25 Gy (5 Gy/fraction) on the overlap area between the PTV and the PRV OARs. SBRT was delivered with Volumetric Modulated Arch Therapy (VMAT) using a LinAc (18 pts) or with 3DCRT and IMRT system (7 pts). On-line daily volumetric image-guided RT was performed

Results: Median follow up time after SBRT was 8.6 months (range 2.3-15.6 months). All pts completed the planned treatment. Overall, a LCR of 72% was obtained (18/25 pts). 14 pts had stable disease (56%), 4 pts a radiographic response (16%) and 7 pts had local progression (28%). No complete response was obtained. Local Progression Free Survival (LPFS) from diagnosis was 87% at 12 months and 74% at 18 months. At the end of follow up 22 pts were alive, with a median PFS of 14.0 months and a median OS of 15.0 months from the time of diagnosis. Tumor relapse after SBRT occurred in 15 pts (60%): local progression in 2 pts, distant progression in 8 pts and a combination of both in 5 pts. No acute or late grade ≥3 toxicities were observed

Conclusion: In our experience, SBRT for unresectable pancreatic cancer is an effective treatment option, able to achieve a high local control rate. SIP allows to deliver high radiation doses to the target with a favorable toxicity profile, even if a larger case series with a longer follow-up period is necessary to draw definitive conclusions