Linac-based stereotactic body radiation therapy for unresectable locally advanced pancreatic cancer: risk-adapted dose prescription and image-guided delivery

Abstract

Background: Stereotactic body radiation therapy (SBRT) represents a new treatment option for locally advanced pancreatic cancer (LAPC). An accurate treatment planning with risk-adapted dose prescription with adherence to specific dose constraints for organs at risk (OARs) and the use of daily cone beam CT (CBCT) for image guidance could allow an effective and safe treatment delivery. Here, feasibility and efficacy of SBRT in LAPC treated in our cancer care center are reported.

Patients and methods: 33 unresectable LAPC patients underwent SBRT. In order to respect OAR dose constraints, a risk-adapted dose prescription strategy was adopted, choosing between the following schedules: 42 Gy or 45 Gy in 6 daily fractions with a biologically effective dose (BED) > 70 Gy₁₀ or 36 Gy/6 fractions (estimating a BED 57.6 Gy₁₀). SBRT was delivered with volumetric modulated arc technique (VMAT) and flattening filter-free (FFF) mode. Image guidance was performed by means of CBCT before every treatment session. The patients were evaluated at the end of treatment for acute toxicity and at 3, 6, and 12 months for late toxicity and treatment response.

Results: At the time of analysis, the median follow-up was 18 months (range 5-34 months). Prior to SBRT, 24 out of 33 patients received induction chemotherapy. Although all patients were previously judged as unresectable, 6 out of 33 (18%) underwent surgery after SBRT; all of them received a BED > 70 Gy₁₀. One-year LC and OS were 81% and 75%, respectively. A total of 12 patients (37%) had an extra-pancreatic progression. No cases of ≥G3 acute or late toxicity were reported.

Conclusion: In our experience, risk-adapted dose prescription and image-guided SBRT represents an effective treatment option for LAPC patients.

Keywords: IGRT; IMRT; Local progression; Pancreatic cancer; Radiation therapy; SBRT; Toxicity.