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We aimed to report the efficacy and tolerance of Stereotactic Body Radiation Therapy (SBRT) after induction chemotherapy (ICT) for the treatment of unresecable locally advanced pancreatic cancer (LAPC).

We performed a single-institution retrospective review of patients with LAPC treated with SBRT after ICT from 2015-2020. The median dose was 37.5 Gy (range: 32.5 - 40 Gy) in five fractions. Most patients were treated by mFOLFIRINOX followed by CyberKnife robotic SBRT using fiducial markers for tracking. Median prescription isodose was 77% (range: 74 – 78). Coverage of the target volume at the prescribed dose was degraded in order to comply with dose constraints to organs at risk. Endpoints included local control, progression free survival, overall survival, and toxicity calculated from the date of radiological diagnosis. All baseline and follow up CT scans were reviewed by an independent radiologist using RECIST 1.1 criteria. Each progression has been classified according to location: in-field, marginal, or out-field.

Fifty-two patients were treated, with a median follow-up of nineteen months. All pancreatic tumors were adenocarcinoma assessed to be non resectable LAPC. The 1 and 2 year-local-control rates after ICT and SBRT were 71% and 21% respectively with a median local control of 22.7 months (Figure 1). Progression free survival at 1 and 2 years were 61% and 13%, and overall survival rates were 83% and 35% at 1 and 2 years respectively. About half of patients experienced acute toxicity and 13.4% a late toxicity. Grade 3-4 acute toxicities were experienced by 3.8% of patients, the most common being abdominal pancreatic pain. Grade 3-4 late toxicities were experienced by 7.7% of patients, the most common being gastrointestinal perforation, with one treatment related death. Majority of patients declared a distant or outfield relapse (46.2%), compared to marginal or in-field recurrence (17.3% and 28.8% respectively) (figure 2).

Figure 1. Overall Survival - Local control - Progression free-survival,from diagnosis

Figure 2. Recurrences’ profil types

Chemoradiotherapy has shown a benefit in terms of local control in LAPC after ICT, without benefit in survival. Our results suggest that SBRT may be considered as an alternative option with a much shorter treatment time and less acute toxicity for equivalent local control and acceptable late toxicity.